efecto de la frecuencia de ordeño sobre la producción ... · ganadería caprina al sostenimiento...

Alexandr Torres KrupijOctubre 2013

Efecto de la frecuencia de ordeñosobre la producción,

fraccionamiento lechero y parámetros de calidad

de la leche en las cabras canarias

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Anexo II

UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA

Departamento: Instituto Universitario de Sanidad Animal y Seguridad Alimentaria

Programa de Doctorado: Sanidad Animal

Título de la Tesis

“EFECTO DE LA FRECUENCIA DE ORDEÑO SOBRE LA

PRODUCCIÓN, FRACCIONAMIENTO LECHERO Y PARÁMETROS

DE CALIDAD DE LA LECHE EN LAS CABRAS CANARIAS”

Tesis Doctoral presentada por D. Alexandr Torres Krupij

Dirigida por los Dres. D. Anastasio Argüello Henríquez y D. Juan Capote Álvarez

Las Palmas de Gran Canaria, a 15 de julio de 2013

Anastasio Argüello Henríquez

El Doctorando, El Director,

Alexandr Torres Krupij

El Director,

Juan Capote Álvarez

ANASTASIO ARGÜELLO HENRÍQUEZ, PROFESOR TITULAR DE

UNIVERSIDAD EN EL DEPARTAMENTO DE PATOLOGÍA ANIMAL,

PRODUCCIÓN ANIMAL, BROMATOLOGÍA Y TECNOLOGÍA DE LOS

ALIMENTOS DE LA FACULTAD DE VETERINARIA DE LA

UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA

INFORMA:

Que Alexandr Torres Krupij, Ingeniero Químico, ha realizado bajo mi

dirección y asesoramiento el presente trabajo titulado “EFECTO DE LA

FRECUENCIA DE ORDEÑO SOBRE LA PRODUCCIÓN,

FRACCIONAMIENTO LECHERO Y PARÁMETROS DE CALIDAD

DE LA LECHE EN LAS CABRAS CANARIAS” considerando que reúne

las condiciones y calidad científica para optar al grado de Doctor en

Veterinaria.

Las Palmas de Gran Canaria, julio 2013

Fdo. Anastasio Argüello Henríquez

JUAN CAPOTE ÁLVAREZ, DIRECTOR DE LA UNIDAD DE

PRODUCCIÓN ANIMAL, PASTOS Y FORRAJES DEL INSTITUTO

CANARIO DE INVESTIGACIONES AGRARIAS

INFORMA:

Que Alexandr Torres Krupij, Ingeniero Químico, ha realizado bajo mi

dirección y asesoramiento el presente trabajo titulado “EFECTO DE LA

FRECUENCIA DE ORDEÑO SOBRE LA PRODUCCIÓN,

FRACCIONAMIENTO LECHERO Y PARÁMETROS DE CALIDAD

DE LA LECHE EN LAS CABRAS CANARIAS” considerando que reúne

las condiciones y calidad científica para optar al grado de Doctor en

Veterinaria.

Las Palmas de Gran Canaria, julio 2013

Fdo. Juan Capote Álvarez

Alexandr Torres KrupijLas Palmas de Gran Canaria, Octubre 2013

FACULTAD DE VETERINARIA

TESIS DOCTORAL

EFECTO DE LA FRECUENCIA DE ORDEÑOSOBRE LA PRODUCCIÓN,

FRACCIONAMIENTO LECHEROY PARÁMETROS DE CALIDAD DE LA LECHE

EN LAS CABRAS CANARIAS

AGRADECIMIENTOSNi en estas líneas ni en un libro entero puedo plasmar mi gratitud a las personas e ins-tituciones que han hecho posible la realización de esta tesis. Soy de los que prefieren mostrar cotidianamente mi agradecimiento de muchas formas, sin necesidad de esperar al final para enumerar una a una las personas que han sido importantes en este trabajo. Sin embargo, me gustaría mencionar:

• AlINIAporlaoportunidaddefinanciarmidoctorado,sinlocual,hubiesesido prácticamente imposible continuar con la formación.

• Muchas gracias al equipo de trabajo del Departamento de ProducciónAnimaldelaULPGCyalaUnidaddeProducciónAnimal,PastosyForrajesdel ICIA. A los “jefes” de dichos grupos, por mostrarme las directrices a seguir y contribuir a lograr los objetivos pautados. A mis compañeros de laboratorio (estudiantes y personal técnico) por brindarme su amistad yayudadesinteresada.Porcompartirtantosmomentosagradables.Mesiento orgulloso de haber pertenecido a estos grupos.

• EspecialmentegraciasalpersonaldelaEscueladeCapacitaciónAgrariade Arucas, por hacer que mi estancia fuese tan entrañable, fueron como una familia para mí y nunca los olvidaré.

• Porúltimo,menciónespecialaesaspersonas,queaunquenopertenez-can a este mundo de cabras, experimentos-resultados y papers, me ani-maron en su momento a empezar un doctorado, a continuar cuando las fuerzas disminuían, y a darme el empujón final con alegría y esperanza. Graciasdecorazón.

Textos:Instituto Canario de Investigaciones Agrarias. Finca“Isamar”,Ctra.deElBoqueróns/n,ValleGuerra.LaLaguna.Tenerife.38270.Facultad de Veterinaria de la Universidad de Las Palmas de Gran Canaria. CampusUniversitariodeArucas.Arucas.35416.

Diseño y cuidado editorialMónicaPedrós

Fotografía de portadaFermín Correa

INDICEINTRODUCCIÓN 21

ARTÍCULO 1 69

ARTÍCULO 2 75

MANUSCRITO 3 83

MANUSCRITO 4 103

MANUSCRITO 5 123

CONCLUSIONES 145

INTRODUCCIÓN

INTRODUCCIÓN

21

1. El sector caprino

1.1. El caprino a nivel mundial

1.1.1.Generalidades

Lacabrafuedelosprimerosanimalesdomesticadosporelhombre,haceunos10500años,

contribuyendoaldesarrollode laagriculturaduranteelperiodoneolítico (Fernándezycol., 2006).

Desde entonces entró a formar parte de la alimentación del ser humano, proporcionándole leche

ycarne,ademásdepiel,peloyestiércol (VigneyHelmer, 2006). La importantecontribuciónde la

ganadería caprina al sostenimiento alimentario de la humanidad ha hecho que en la actualidad se

encuentre en regiones geográficas que difieren notablemente en clima, topografía y fertilidad, debido

asugranrusticidadyadaptabilidad(Devendra,1987).

Las cabras pueden adaptarse a una amplia gama de sistemas de intensificación que van de

un extremo al otro: por un lado, las razas lecheras mejoradas explotadas en condiciones intensivas

en las zonas templadas de Europa o América del Norte, en ciertas zonas favorables de clima tropical

húmedo,oensuperficiesirrigadasdeclimatropicalsecoy,porotrolado,laspoblacioneslocalesque

se mantienen en regiones muy áridas en las que los demás rumiantes difícilmente pueden resistir,

talescomolaszonasdesérticasdeÁfricaodelMedioOriente(BoyazogluyMorand-Fehr,1987).

1.1.2.Poblacióncaprinayproducciónlechera

La población caprina a nivel mundial ha incrementado su censo de forma importante durante

losúltimos40años,muchomásqueloscensosdebovinoyovino(Tabla1),locualsugiereelcreciente

interésporpartedelapoblaciónenlosproductoslácteosderivadosdelacabra(Dubeuf,2005).

Tabla 1. Población mundial de bovino, ovino y caprino en los últimos 40 años (millones de cabezas). (FAOSTAT, 2011).

Año Bovino Ovino Caprino2010 1427,5 1078,3 909,82000 1313,2 1059,7 751,41990 1298,4 1207,9 591,11980 1217,0 1098,7 464,31970 1081,6 1063,3 377,7

Efecto de la frecuencia de ordeño sobre la producción, fraccionamiento lechero y parámetros de calidad de la leche en las cabras canarias

22

Sinembargo, ladistribucióndelcaprinoesbastantedesigualanivelmundial.SegúnlaOr-

ganizacióndelasNacionesUnidasparalaAlimentaciónylaAgricultura(FAO),enelaño2011Asia

concentrabael61,6%delcensototal,mientrasqueÁfricacontabaconel31,6%.Encontraste,Europa

yAméricasólotienenel1,9%y4,3%,respectivamente.Así,paísescomoChina,India,Pakistán,Ban-

gladesh,yNigeria(Figura1)estánalacabezaencuantoapoblacióndecabras,representandoun

valioso sustento para numerosas familias de escasos recursos.

Figura1.Principalespaísesenpoblacióncaprinaenelaño2011.(FAOSTAT,2011).

DeacuerdoconlaFAO,laproduccióndelechedecabraenelmundoduranteelaño2011fue

deaproximadamente15millonesdetoneladas,loquerepresentóel2,2%deltotaldelalecheprodu-

cidaanivelmundial.Europa,consóloel5%deltotaldelganadocaprinolechero,produjocasiel20%

del volumen de leche total de esta especie. Cabe señalar, que en algunos países de África y Asia, las

estadísticas no registran el verdadero valor de la producción, debido a la dificultad para hacer los

censos, por la dispersión de los rebaños, y porque prácticamente toda la leche se destina al consumo

de la unidad familiar.

1.1.3.Biodiversidadcaprina

Entrelos900millonesdecabrasanivelmundial,untotalde570razashansidodefinidas.Los

paísesenvíasdedesarrolloconcentranel60%deltotaldelasrazas(Galal,2005).EnEuropaseen-

cuentran los genotipos con mayor producción lechera como la Saanen, Alpina, Nubia o Toggenburg

(Figura2).Sinembargoestecontinenteposeelamenordiversidadgenética,debidoalosprocesosde

mejora productiva, en los que han desaparecido las razas menos competitivas.

INTRODUCCIÓN

23

Figura2.Principalesrazascaprinaslecheras.A:Saanen;B:Alpina;C:Nubia;D:Toggenburg.(BreedStandards,www.dairygoatjournal.com).

1.2. El caprino en España

1.2.1.Generalidades

Durante muchos años, la cabra en España ha jugado un destacado papel en el abastecimiento

de leche para el consumo de la población. La leche obtenida era destinada al consumo familiar, mayo-

ritariamentedeformadirecta,aunqueunafracciónvariablesegúncasos,eratransformadaenqueso,

elaboradoen lapropiaexplotaciónpormétodosartesanales (Esteban-Muñoz,2008). Laganadería

caprina ha estado ligada tradicionalmente a zonas rurales poco productivas desde el punto de vista

agrícola, dado que las cabras tienen una gran capacidad para el aprovechamiento de los pastos de

escasa calidad. Esta característica ha hecho que el ganado caprino jugase un papel importante en el

mantenimientodezonasmarginalesydelapoblaciónasociadaaellas.Aúnhoyendía,enEspaña,el

86%delapoblacióncaprinaseencuentraenlasllamadasáreasmenosfavorecidas(Rancourtycol.,

2006),aunquelossistemasdeexplotaciónhancambiadosustancialmente.


EnEspaña,segúnlaFAO,lapoblacióndecaprinosdeaptitudlecheraseestimóalrededorde

los1,2millonesdecabezasenelaño2011.Laevolucióndelcensocaprinoenlosúltimos20años(Fi-

gura3)hasufridooscilacionessignificativas,comoconsecuencia,entreotrosaspectos,delavaria-

bilidadenlospreciosdelaleche.Sinembargo,laproducciónlecherasobrepasólas540000toneladas

enel2011,conunincrementoanualmediodel4%durantelasúltimasdosdécadas,principalmente

debido a la mejora genética y alimenticia, lo cual ha permitido optimizar el rendimiento lechero.


24

Figura3.EvolucióndelganadocaprinolecheroyproduccióndelechedecabraenEspañaenlosúltimos20años.(FAOSTAT,2011).

Ladistribucióndelcaprinoenlageografíaespañolaesmuyirregular(Figura4).EnCanariasy

enelsurdelaPenínsulaIbéricaseconcentraalrededordel80%delcensodecabras.Lalargatradi-

ción de los cabreros de dichas áreas geográficas y la presencia de razas caprinas de alta producción

de leche, además de la situación agroclimática, han favorecido el desarrollo del caprino en estas

regiones(Esteban-Muñoz,2008).

Figura4.Distribucióndelganadocaprinoporcomunidadesautónomasen2011.(MAGRAMA,2011).

Introducción

Página 9

Figura 3. Evolución del ganado caprino lechero y producción de leche de cabra en España en los últimos

20 años. (FAOSTAT, 2011).

La distribución del caprino en la geografía española es muy irregular (Figura 4).

En Canarias y en el sur de la Península Ibérica se concentra alrededor del 80% del censo

de cabras. La larga tradición de los cabreros de dichas áreas geográficas y la presencia

de razas caprinas de alta producción de leche, además de la situación agroclimática, han

favorecido el desarrollo del caprino en estas regiones (Esteban-Muñoz, 2008).

Figura 4. Distribución del ganado caprino por comunidades autónomas en 2011. (MAGRAMA, 2011).

200

400

600

800

1000

400

800

1200

1600

2000

1991 1995 1999 2003 2007 2011

Miles de

tone

lada

s de

leche

Miles de

cab

ezas de gana

do

Año

Ganado caprino lechero Producción lechera

Introducción

Página 9

Figura 3. Evolución del ganado caprino lechero y producción de leche de cabra en España en los últimos

20 años. (FAOSTAT, 2011).

La distribución del caprino en la geografía española es muy irregular (Figura 4).

En Canarias y en el sur de la Península Ibérica se concentra alrededor del 80% del censo

de cabras. La larga tradición de los cabreros de dichas áreas geográficas y la presencia

de razas caprinas de alta producción de leche, además de la situación agroclimática, han

favorecido el desarrollo del caprino en estas regiones (Esteban-Muñoz, 2008).

Figura 4. Distribución del ganado caprino por comunidades autónomas en 2011. (MAGRAMA, 2011).

200

400

600

800

1000

400

800

1200

1600

2000

1991 1995 1999 2003 2007 2011

Miles de

tone

lada

s de

leche

Miles de

cab

ezas de gana

do

Año

Ganado caprino lechero Producción lechera

INTRODUCCIÓN

25

En el año 2011, Andalucía fue la comunidad autónoma con mayor producción de leche de

cabra,conmásdel40%deltotalespañol,seguidaporCanariasyCastillaLaMancha(Figura5).La

leche de cabra que se obtiene se destina mayoritariamente a la fabricación de queso, y en menor me-

didaalconsumodirecto.SegúndatosdelMinisteriodeAgricultura,AlimentaciónyMedioAmbiente

(MAGRAMA),enelaño2010,únicamenteel40%delalechedecabrarecogidaenEspañasedestinó

a la fabricación de queso puro de cabra, siendo el resto de la leche destinada a quesos de mezcla,

otrosproductosfermentadosoexportadaaotrospaíses.Sehanidentificadountotalde28quesos

purosdelechedecabray21demezclaconlechedeovejay/ovaca(Ramírez,2009).Así,encontramos

quesostípicosenAndalucía(SierradeCádiz,QuesitosdeZuheros,SierradeCazorla,Malagueño),

Murcia(Murciaalvino),Extremadura(Ibores),yCanarias(Majorero,Palmero,Herreño),entreotros.

En general, se trata de quesos de calidad donde la industria ha mantenido los tipos tradicionales y los

criterios básicos de elaboración, donde algunos de ellos han accedido a los mercados internaciona-

lesconéxito(Esteban-Muñoz,2008).

Figura5.DistribucióndelacantidaddelecheproducidaporComunidadesAutónomasenel2011.(MAGRAMA,2011).


España cuenta con un patrimonio genético caprino que ocupa un lugar preferente en Europa.

La alta capacidad de las razas autóctonas para producir leche en zonas desfavorecidas, conduce a

que la explotación de estos animales adquiera un significado especial en los campos económico y

Introducción

Página 10

En el año 2011, Andalucía fue la comunidad autónoma con mayor producción de

leche de cabra, con más del 40% del total español, seguida por Canarias y Castilla La

Mancha (Figura 5). La leche de cabra que se obtiene se destina mayoritariamente a la

fabricación de queso, y en menor medida al consumo directo. Según datos del

Ministerio de Agricultura, Alimentación y Medio Ambiente (MAGRAMA), en el año

2010, únicamente el 40% de la leche de cabra recogida en España se destinó a la

fabricación de queso puro de cabra, siendo el resto de la leche destinada a quesos de

mezcla, otros productos fermentados o exportada a otros países. Se han identificado un

total de 28 quesos puros de leche de cabra y 21 de mezcla con leche de oveja y/o vaca

(Ramírez, 2009). Así, encontramos quesos típicos en Andalucía (Sierra de Cádiz,

Quesitos de Zuheros, Sierra de Cazorla, Malagueño), Murcia (Murcia al vino),

Extremadura (Ibores), y Canarias (Majorero, Palmero, Herreño), entre otros. En general,

se trata de quesos de calidad donde la industria ha mantenido los tipos tradicionales y

los criterios básicos de elaboración, donde algunos de ellos han accedido a los mercados

internacionales con éxito (Esteban-Muñoz, 2008).

Figura 5. Distribución de la cantidad de leche producida por Comunidades Autónomas en el 2011.

(MAGRAMA, 2011).

Resto 6%

Castilla y León 7%

Castilla La Mancha

13%

Murcia 7%

Extremadura 5%

Andalucía 43%

Canarias 19%


26

social(Castelycol.,2010).ElRealDecreto2129/2008,de26dediciembre,estableceelprogramana-

cional de conservación, mejora y fomento de las razas ganaderas. En el mismo se definen a las razas

autóctonas caprinas como de fomento o de protección especial.

LasrazasMurciano-GranadinayMalagueña(Figura6)quejuntoconlasrazasMajorera,Pal-

mera y Tinerfeña, se encuentran en expansión por su censo y organización, son las consideradas

comodefomento,mientrasqueelgrupodeprotecciónespecialcompuestoporotras16razas,entre

lasquedestacanlaPayoyaylaFlorida,disponenensuconjuntodeunapoblaciónreducida,debido

a una menor producción lechera, al fuerte aumento de los costes de producción, además de los pro-

blemasrelacionadosconlaescasezdecabreros(Esteban-Muñoz,2008).

Figura6.CabrasMurciano-Granadina(izquierda)yMalagueña(derecha).(MURCIGRANyCABRAMA).

1.3. El caprino en las Islas Canarias

1.3.1.Generalidades

En Canarias, la explotación caprina ha constituido tradicionalmente un importante recurso eco-

nómicoque,enépocasprehispánicas,llegóaserelmásimportantedelosaborígenes(Figura7)(Fresno

ycol.,1992).Elganadoqueellosmanejaban,deorigendesconocidohastaelmomento,lesservíacomo

fuente de alimentación (carne, leche) y les proporcionaba pieles, huesos e incluso productos con utili-

dadmedicinal(manteca).Esdesuponerqueestosanimales,constituíanunarazarústicamásomenos

uniforme, si bien existían por aquella época, dos tipos de ganado caprino, uno doméstico o “jairo”, y otro

salvajeo“guanil”,cuyosúltimosejemplaresdesaparecieronenladécadadeloscincuentadesuúltimo

reducto:LaCalderadeTaburienteenlaisladeLaPalma(Capoteycol.,1993).

INTRODUCCIÓN

27

Figura7.MuraldeAntonioGonzálezSuárezsobrelavidaaborigenenCanarias,enelsalóndeplenosdelAyuntamientodelosLlanosdeAridane.(CRDOPQuesoPalmero).

Desde finales del siglo XV, Canarias se convirtió en paso obligado para las rutas transoceá-

nicas, lo que significó aportes genéticos a la población caprina ya existente. Así, se puede observar

en unas determinadas características (capas, cornamenta) la influencia que en su día tuvieron ca-

brasportuguesas(Charnequeira,Serpentina),españolas(Pirenaica,Granadina),europeas(Saanen)

y africanas (Nubia), y que junto con las distintas condiciones medioambientales de cada isla (clima,

orografía, pastos), han terminado por configurar los tipos caprinos que hoy constituyen el archipiéla-

go(Capoteycol.,1998).


En la actualidad las cabras tienen un importante peso específico dentro del subsector gana-

dero, y su población está distribuida en todas las islas, aunque la mayor parte del censo se concentra

enFuerteventura,GranCanaria,yTenerife(Tabla2).


28

Tabla 2. Distribución de la cabaña caprina por islas en el año 2010. (Instituto Canario de Estadística, 2010).

Isla Nº Cabezas %Fuerteventura 116226 34,8GranCanaria 82742 24,8Tenerife 61434 18,4LaPalma 27651 8,3Lanzarote 24208 7,2LaGomera 11175 3,3El Hierro 10481 3,1

Enlasúltimasdécadas,elcaprinodelasislassehaexportadoaregionesmediterráneasy

tropicales donde se ha adaptado con bastante facilidad. Así, en países como Venezuela, la cabra

“Canaria”(Figura8),quenoesmásqueunaamalgamadelastresrazasdelasislas,conpredomi-

nanciadelarazaMajorera,estámuybienvaloradaporlosganaderosquedestacansurusticidady

altaproductividad.Porello,cercadel95%delasexplotacionesintensivasubicadasenesepaísem-

pleandicharaza(TorresyCapote,2011).Adicionalmente,larecienteintroduccióndecabrasderaza

MajoreraenSenegalylosrespectivosinformestécnicosconfirmanlaexcelenteadaptacióndeesas

cabrasalmedioambientesubsahariano(Capoteycol.,2012).

Figura8.Cabras,concrucedeCanaria,enunaexplotaciónganaderaenelestadoLaraenVenezuela.(TorresyCapote,2011).

INTRODUCCIÓN

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SegúnelInstitutoCanariodeEstadística,en2010seprodujeronmásde85000toneladasde

lechedecabra,cuyafinalidadprincipalfuelaproduccióndequeso(Figura9),lamayorpartedelcual

se elabora con leche cruda usando métodos tradicionales y es consumido tras breves periodos de

maduración(7días)(Fresnoycol.,2008).Ademásdelariquezagenéticacaprinayforrajera,Canarias

tiene una excepcional situación sanitaria debido al estar oficialmente libre de brucelosis caprina y

ovina(Sánchez-Macíasycol.,2011),locualpermiteaaproximadamente500productoresartesanos

laventadequesosde lechecrudaconmenosde60díasdemaduración(FresnoyÁlvarez,2007).

Destacalaelaboracióndedosquesospurosdelechedecabra,MajoreroyPalmero,yunquesode

mezcladeovejaconlechedevacay/ocabra,el“QuesoFlordeGuíayQuesodeGuía”queposeen

DenominacióndeOrigenProtegida(DOP),aunqueenesteúltimocaso,lalechedecabrapuedeser

utilizadaenun10%comomáximo.

Figura9.Quesoscanarios.(ICCA).


Hastal985todoslostrabajospublicadosincluíanalosindividuosdelapoblacióncaprinaca-

naria dentro de una raza en la que se admitían las más variadas morfologías. Durante ese mismo

añosepublicóenelBoletínOficialdelEstado(BOE)laOrdenporlaqueseaprobabanlasnormas

reguladorasdelLibroGenealógicoydeComprobacióndeRendimientoparalaAgrupaciónCaprina


30

Canaria,dondeseeliminóeltérmino“raza”.Capote(1985)postulólahipótesisdelaexistenciadetres

razasdiferenciadas,basadaenlaopinióndelosganaderos,ydenominadassegúnsuisladeorigen:

Majorera(Fuerteventura),Palmera(LaPalma),yTinerfeña(Tenerife),sibienestaúltimapodríaestar

divididaenotrasdosquesesituaríanenlafranjaNorte(húmeda)ySur(árida)delaisla.Posterior-

mente,losestudiosmorfológicos(Capoteycol.,1998)ygenéticos(Martínezycol.,2006)confirmaron

dichahipótesis.Elreconocimientodelastresrazas(Figura10)estárecogidoenelCatálogoOficialde

RazasdeGanadodeEspaña(BOE,OrdenAPA2420/2003,de28deagosto).

Figura10.Razascaprinascanarias.A:Majorera;B:Palmera;C:Tinerfeña.(GobiernodeCanarias).

A continuación se describen las tres razas caprinas canarias reconocidas oficialmente:

∑ Raza Majorera.

DebesunombrealaIsladeFuerteventura(Maxorataenlaépocaprehispánica)lugardonde

seformóydondeseencuentraelmayornúcleodeanimalesdelaraza,aunquesucríaseextiendepor

todaslasislasdelarchipiélago.Engeneral,lacabraMajoreraseadaptabienalosdiferentessiste-

mas de explotación, desde el pastoreo en zonas áridas, a la estabulación permanente, con elevados

rendimientos en la producción de leche.

Existe coincidencia en admitir que cuando llegaron los castellanos a las islas, a finales del

siglo XV, existía una población caprina adaptada al medio que había permanecido aislada genética-

mentedelrestodelmundo.Posteriormente, la llegadadenuevasetnias, incidieronsobreel fondo

genético de la población caprina prehispánica, dejando rasgos en la población actual de las islas y

querecuerdanatroncoscomoelPirenaicooelNubianoafricano(Amillsycol.,2004).

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31

Elprototipo racial respondea lassiguientescaracterísticas (Figura11):Cabezade tamaño

grande, con perfil fronto-nasal recto o subconvexo, con orejas grandes e inclinadas hacia abajo. Los

cuernos pueden ser tipo prisca o de tipo aegagrus, en arco hacia atrás. La línea dorso-lumbar es rec-

ta. El pelo se presenta generalmente uniforme, corto y raso, y capa policromada. Ubre de color negro

o pizarra, tipo globosa o abolsada, de amplia inserción, con pezones bien diferenciados y, a veces de

implantaciónlateral(Esteban-Muñoz,2008).

Figura11.CabraMajorera.(FEAGAS).

LaproducciónmediadelascabrasderazaMajoreraesde551,3kgdelecheen210díasde

lactación.Porotraparte,unelevadoporcentajedecabrasmantienenduranteeseperiodounapro-

ducciónmediasuperiora2kgdelechepordía.Conunacomposiciónmediadelalechede:Grasa=

3,94%;Proteína=3,90%;Lactosa=4,55%;ExtractoSeco=13,19%(Fresno,1993).

Hay que tener en cuenta que una buena parte de la leche de estas cabras es destinada a la

elaboración de queso artesanal o industrial, el cual se consume después de unos días de oreo, o bien

se deja madurar largo tiempo, en ambiente templado y seco. El queso que se va a conservar más

tiempo puede untarse con aceite, pimentón y/o gofio, lo que le confiere características peculiares.

Su masa al corte aparece compacta, de textura cremosa y sabor acídulo y algo picante. Es de color

blanco,tomandounligerotonomarfileñoenquesoscurados(FresnoyÁlvarez,2007).


32

∑ Raza Palmera.

TienesuorigenenlapoblacióncaprinaprehispánicaenlaisladeLaPalma.Alserestaislaun

lugardepasoenlasrutasvelerascondestinoaAmérica,larazaPalmerasevioinfluenciadaporlas

razasdelsuroestedelaPenínsulaIbérica.Sinembargo,estegenotipotuvounmayoraislamientoque

las otras razas canarias, lo que la aproxima más a la cabra prehispánica, y sustenta su diferenciación

genética, que permite una extraordinaria rusticidad y capacidad de adaptación a zonas abruptas de

montaña(Martínezycol.,2006).

En la década de los setenta la raza experimentó cruces con animales pertenecientes a la po-

blaciónMajoreraconobjetodeaumentarlaproduccióndeleche,debidoalaerróneapolíticaenese

momento de considerar a las tres razas canarias como una sola. Aquellos cruzamientos implicaron un

trabajo posterior enorme y complicado, aunque afortunadamente con resultados satisfactorios, para

eliminar los genes foráneos ya que los híbridos no se adaptaban a las condiciones de explotación de

laIsladeLaPalma(Capoteycol.,1993).

Elprototipo racial respondea lassiguientescaracterísticas (Figura12):Cabezade tamaño

pequeño, corta y ancha, con perfil fronto-nasal recto o subcóncavo, orejas más bien cortas y una

cornamenta destacada, con predominancia del tipo heteronima. Tronco largo, con línea dorso-lumbar

recta. En sus capas predomina el color rojizo y el pelo es de longitud media. Ubre más recogida que

en las otras razas canarias, de tipo globosa, color negro o pardo, y con pezones más bien pequeños

(Esteban-Muñoz,2008).

Figura12.CabraPalmera.(CRDOPQuesoPalmero).

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33

Laproducciónmediatipificadaa210díasdelactación,esde362,6kgdeleche,conunapro-

duccióndegranpersistencia,loquepermiteampliarelperiododelactacióna240-270días.Lacalidad

mediadelalecheesde:Grasa=4,06%;Proteína=4,21%;Lactosa=4,66%;ExtractoSeco=13,75%

(Fresno,1993).

LaproduccióndelechedelacabraPalmeravadestinadaalafabricacióndequesodetipo

artesanal. Se trata de un queso graso o extragraso, elaborado con leche cruda y entera, y se co-

mercializatantotierno(de8a20días),comosemicurado(21a60días)ycurado(apartirde60días).

El sabor es franco y láctico, muy mantecoso y con un ligero y agradable aroma ahumado (Fresno y

Álvarez,2007).

∑ Raza Tinerfeña.

SibienenelCatálogoOficialesconsideradacomounaúnicapoblación,estudiosmorfoló-

gicos y genéticos señalan suficientes evidencias para considerar dos grupos independientes en el

norteysurdelaisladeTenerife(Capoteycol.,1998;Martínezycol.,2006).Así,existiríaelecotipo

Norte, con gran influencia del tronco pirenaico, y el ecotipo Sur, reducido en pureza por sus cruces

concabraMajorera.Aligualquelasotrasdosrazas,lacabraTinerfeñapresentaunagranrusticidad

y elevada aptitud para la producción de leche.

Elprototiporacialtienelassiguientescaracterísticas(Figura13):Cabezadetamañopropor-

cionado con el cuerpo, el ecotipo Norte dispone de un perfil fronto-nasal recto o subconvexo, mien-

trasqueenelSurcasisiempreesrecto.Ambastienencornamentatipoprisca.Orejasdegrantama-

ño, inclinadas hacia abajo en las cabras del Norte, y de menor tamaño en cabras de la zona Sur. Los

caprinos del Norte se caracterizan por presentar pelo largo y colores oscuros, principalmente negro

y con alguna frecuencia castaño. Los caprinos del Sur tienen el pelo corto y disponen de una capa

multicolor.Laubredeestascabras,engeneralpresentanuntiposimilaraldelacabraMajorera,con

pezones pequeños y situados con alguna frecuencia en posición lateral. En la cabra Tinerfeña Norte,

la forma de la ubre, frecuentemente globosa, es más adecuada para el ordeño mecánico en lo refe-

rentealtamañoyposicióndelospezones,quesuhomólogadelSur(Esteban-Muñoz,2008).

LosvaloresasignadosalaproduccióndelechedecabraTinerfeñaen210díasdelactación,

esde421,0kgdeleche,conunacomposiciónde:Grasa=3,91%;Proteína=3,79%;Lactosa=4,46%;

ExtractoSeco=13,13%(Fresno,1993).EnlaisladeTenerife,seelaboraelQuesodeTenerife,obtenido


34

con leche cruda de cabra. Se trata de un queso de graso a extragraso y que se consume preferente-

mente fresco o ligeramente curado, de color blanco intenso y brillante, y sabor muy fresco y acidula-

do,ligeramentesaladoygrasolechosoalpaladar(FresnoyÁlvarez,2007).

Figura13.Cabra Tinerfeña Norte. (ACRICATI).

2. La leche de cabraEn términos generales, la leche de cabra es un líquido blanco opaco, de un sabor ligeramente

azucarado, cuyo olor es poco marcado cuando es recogida con limpieza de animales que tengan un

buen estado de salud. La consistencia es uniforme sin grumos ni copos. De la calidad de la leche

empleada en queserías va a depender gran parte el éxito de las transformaciones y la calidad del

producto final. Nutricionalmente, la leche de cabra es una fuente de proteínas de alto valor biológi-

co y ácidos grasos esenciales, además de minerales y vitamina A. Es de gran importancia para los

infantes por su alto valor nutricional, hipoalergenicidad, así como por su alta digestibilidad debido al

pequeño tamaño de los glóbulos de grasa. Algunos autores han resaltado las propiedades saludables

delalechedecabra(Silanikoveycol.,2010)ysusproductosderivados(RibeiroyRibeiro,2010),justi-

ficando su alta calidad y los beneficios de su consumo. Además, la población del mundo desarrollado

no se preocupa especialmente sobre el costo de los productos en el mercado si al consumir deriva-

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35

doslácteosdecabraspuedeobtenerbeneficiosparalasalud(Mowlen,2005).Actualmenteexisten

revisionesquehanprofundizadoenlascaracterísticasfísico-químicas(Parkycol.,2007),reológicas

(Park,2007)ehigiénico-sanitarias(Raynal-Ljutovacycol.,2007)delalechedecabra.

2.1. Composición químicaLa leche está compuesta principalmente, además del agua, por materia grasa, proteínas,

lactosa, sales minerales, vitaminas, y enzimas. La composición varía apreciablemente de acuerdo a

algunos factores como la raza, la alimentación, el período de lactación, la frecuencia de ordeño, el

estado sanitario de la cabra, entre otros.

2.1.1.Grasa

El contenido de grasa es el componente más variable cuantitativa y cualitativamente en la

leche. Los glóbulos de grasa de la leche de cabra son en general más pequeños y más finos que en

lalechedevaca(3,5vs.4,6µm,respectivamente)(Park,2006).Acausadesureducidotamañoyla

uniformidad de su distribución, los glóbulos de la leche de cabra ingerida quedan más dispersos y,

como resultado, las enzimas digestivas humanas, al actuar sobre ellos, los desintegran de forma más

rápida y completa.

No se han encontrado diferencias apreciables en el mecanismo de secreción de los glóbulos

de grasa en cabra, oveja y vaca, teniendo estos glóbulos una estructura y composición similar entre

lastresespecies(Scolozziycol.,2003).Respectoalosácidosgrasosqueformanpartedelaleche

decabra,cincodeellosrepresentanmásdel75%:cáprico(C10:0),mirístico(C14:0),palmítico(C16:0),

esteárico(C18:0)yoleico(C18:1)(Chilliardycol.,2006).

2.1.2.Proteína

En cuanto a las proteínas de la leche, éstas se dividen habitualmente como caseínas y pro-

teínas séricas, aunque se pueden encontrar otras proteínas minoritarias, como inmunoglobulinas,

lactoferrina, transferrina, ferritina, peptona proteasa, prolactina, etc. El contenido total de proteínas

es uno de los principales criterios de calidad usados como sistema de pago de la leche de cabra en

muchospaíses(Pirisiycol.,2007).


36

Engeneral,laß-caseínaeslaprincipalcaseínaenlalechedecabra(Tziboula-Clarke,2003).

Laproporcióndelas4caseínasmayoritariasenlalechedecabraestádeterminadaporpolimorfis-

mos genéticos, pero en general el orden es ß-caseína > αS2-caseína > αS1-caseína>k-caseína.De

media, la αS1-caseínarepresentael10%deltotaldelascaseínas,variandode0a25%(Boulangery

col.,1984),dependiendodelgenotipodelanimal.Lasrazascaprinascanarias(Majorera,Tinerfeñay,

especialmente,Palmera)representanuncasoparticulardondeel60%delosalelosdelaαS1-caseína

caprinasondeltipoAyB(Jordanaycol.,1996),porloqueestacaseínaesrelativamenteabundante

en la leche y quesos elaborados a partir de estos animales.

2.1.3.Lactosa

La lactosa es el carbohidrato por excelencia en la leche, el cual está formado por una mo-

lécula de glucosa y otra de galactosa, que también pueden estar presentes de forma individual en

pequeñascantidadeslibres(Park,2006).Lalactosaesdegranimportanciaparamantenerelequili-

brio osmótico entre la corriente sanguínea y las células alveolares de la glándula mamaria durante la

síntesisdelaleche,ysusecreciónenellumenalveolaryelsistemadeconductosdelaubre(Parky

col.,2007).Encabrasesueleencontrarsobre0,2-0,5%menosqueenlalechedevacayoveja.Otros

carbohidratos presentes en la leche de cabra son los oligosacáridos, glicopéptidos, glicoproteínas y

nucleótidos(Parkycol.,2007),perosusfuncioneshansidomuypocoestudiadas.

2.1.4.Vitaminasyminerales

El contenido de macrominerales en la leche de cabra es mucho mayor que el de la leche hu-

mana, con cuatro y seis veces más calcio y fósforo, respectivamente. Comparativamente, la leche de

cabra contiene más calcio, fósforo, potasio, magnesio y cloro, y menos sodio y azufre que la leche de

vaca(Parkycol.,2007).Debidoaquelascabrasconviertentodoelβ-carotenoenvitaminaA,laleche

de cabra presenta mayor cantidad de este compuesto y es mucho más blanca que la leche de vaca.

Tambiéncontienemástiamina,riboflavina,niacina,vitaminaCyvitaminaDquelalechedevaca(Park

ycol.,2007).

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37

2.2. Células somáticasLas células somáticas están presentes en la leche de todos los mamíferos, no tienen capaci-

dadparamultiplicarseyprovienendelpropioanimal.Segúnsuorigen,seclasificanendosgrandes

grupos: células de origen sanguíneo y células epiteliales. Normalmente estas células se encuentran

en la glándula mamaria sana, aunque puede considerarse un indicador de inflamación y/o infección

debido a que en estas situaciones se produce un incremento en el trasvase de leucocitos a la leche

(DasySingh,2000).

En muchos países se han establecido unos criterios de calidad para la leche de acuerdo a

los requerimientos higiénicos, tecnológicos y sensoriales. Estos criterios forman parte de un sistema

de pago que asegura la calidad de los productos finales. En los Estados Unidos, el límite legal en el

recuento de células somáticas (RCS) establecido en leche de cabra por la FDA (Food and Drug Admi-

nistration)esde1millóndecélulas/ml.SinembargoenlaUniónEuropeanohaylímiteparalaleche

de cabras y ovejas, como está dispuesto en los diferentes reglamentos, que establecen los criterios

generalesyespecíficosdehigienequedebencumplirlosproductosalimenticios(Paapeycol.,2007).

Algunosautores(Paapeycol.,2007;Raynal-Ljutovacycol.,2007)haninformadoquelosca-

breros de Estados Unidos tienen dificultades para mantener el RCS en la leche de tanque por debajo

del límite establecido. Como consecuencia, muchas granjas eliminan la leche que excede el límite, lo

cual provoca importantes pérdidas económicas para el sector.

El alto RCS puede ser causado por infección pero también por razones fisiológicas. En las

ubressanasdecabras,elRCSseincrementaprogresivamenteconlaedad(Salamaycol.,2003),du-

rantelalactación(Gomesycol.,2006),ademásdefluctuacionesdeundíaparaotro(Zengycol.,1997),

enlaqueintervienenfactorescomoelcelo(Mehdidycol.,2013)yelestrés(McDougallycol.,2002).

Portanto,laaplicacióndeuncriterioparalaevaluacióndelacalidaddelalecheyparaladetección

de mastitis está sin resolver.

En España ya hay algunas industrias queseras que están pagando la leche de cabra a los ga-

naderossegúnsucomposiciónquímicabásica(grasayproteína)asícomoenfuncióndelacalidad

higiénico-sanitaria (microbiología, RCS), pudiendo aplicarse primas o penalizaciones, tal como se

recoge en la homologación de contrato-tipo de suministro de leche de cabra con destino a su trans-

formaciónenproductoslácteos(OrdenARM/2387/2010,de1deSeptiembre).


38

3. Factores que afectan al rendimiento y composición de la leche

La cantidad de leche producida por una cabra y su composición tienen variaciones como

consecuenciadeungrannúmerodefactores.Estospuedenactuaraisladamenteoencombinación.

Clásicamente, los mencionados factores se han dividido en dos grupos, uno de carácter intrínseco,

atribuido al animal, y otro de carácter extrínseco, debido a las condiciones y circunstancias externas

queactúansobreél.

3.1. Factores intrínsecos

3.1.1.Razaeindividuo

La producción lechera caprina está condicionada por factores genéticos que influyen tanto

sobrelacantidad(Figura14)comoenlacalidaddelalecheproducida.Sinembargo,lasdiferentes

condiciones de cría, alimentación, factores geográficos y climáticos a las que están expuestas las

diferentes razas, hacen difícil evaluar la importancia de este factor, de tal manera que la mayoría de

diferencias dentro de cabras de la misma raza pueden ser explicadas por el efecto rebaño (Capote y

col.,2000).

Figura14.Curvasdelactacióndealgunasrazasdealtaproducción.(AnimalImprovementProgramsLaboratory,2004).

Introducción

Página 27

3.1. Factores intrínsecos

3.1.1. Raza e individuo

La producción lechera caprina está condicionada por factores genéticos que

influyen tanto sobre la cantidad (Figura 14) como en la calidad de la leche producida.

Sin embargo, las diferentes condiciones de cría, alimentación, factores geográficos y

climáticos a las que están expuestas las diferentes razas, hacen difícil evaluar la

importancia de este factor, de tal manera que la mayoría de diferencias dentro de cabras

de la misma raza pueden ser explicadas por el efecto rebaño (Capote y col., 2000).

Figura 14. Curvas de lactación de algunas razas de alta producción. (Animal Improvement Programs

Laboratory, 2004).

Las cabras de alta producción lechera más difundidas en el mundo tienen su

origen o se han seleccionado esencialmente en tres países: Suiza (Saanen y

Toggenburg), Francia (Alpina) e Inglaterra (Anglonubia). Sobre estos animales se han

realizado una gran cantidad de estudios que abarcan la mayoría de los aspectos

relacionados con los individuos y su explotación, destacando aquellos dedicados a la

0,0

1,0

2,0

3,0

4,0

0 50 100 150 200 250 300 350

Prod

ucción

de leche (Kg)

Días de lactación

Alpina

Nubia

Saanen

Toggenburg

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39

Las cabras de alta producción lechera más difundidas en el mundo tienen su origen o se

han seleccionado esencialmente en tres países: Suiza (Saanen y Toggenburg), Francia (Alpina) e

Inglaterra (Anglonubia). Sobre estos animales se han realizado una gran cantidad de estudios que

abarcan la mayoría de los aspectos relacionados con los individuos y su explotación, destacando

aquellosdedicadosa laproducción lechera(Britoycol.,2011;Garcia-Penicheycol.,2012).En los

países, cuyas razas nativas son muy poco productivas, suele ser frecuente el cruzamiento con razas

mejoradas(Kumeycol.,2012;Sanogoycol.,2012).Ladiscutiblefinalidaddeestoscruzamientosesla

de conservar las cualidades de rusticidad y adaptación al medio de las razas nativas pero mejorando

la producción lechera y alargando el tiempo de lactación.

La composición química de la leche también presenta grandes variaciones según la raza,

ligadasalniveldeproduccióndeleche.Enestesentido,Garcia-Penicheycol.(2012)examinaronla

composicióndelalecheenvariasrazasdealtaproduccióndurante3periodos(de1976a1984,de

1985a1994,yde1995a2005),yobservaronincrementosenelporcentajedeproteína,elcualfueva-

riablesegúnlasrazas(7,4%enToggenburg;7,1%enAlpina;6,5%enLaMancha;5,6%enAnglonubia;

3,4%enSaanen).Sinembargo,sóloencontraronincrementosenelporcentajedegrasaenunaraza

(2,1%enAnglonubia).

El estudio detallado de las variantes genéticas de la caseína as1(Ambrosoliycol.,1988;Jor-

danaycol.,1996)permitiórealizarunanuevaclasificacióndelasrazascaprinasenfuncióndesus

frecuencias alélicas. Cabe destacar que la concentración de as1secorrelacionapositivamentecon

las propiedades de coagulación de la leche, y que nuevos trabajos genéticos están enfocados en la

mejoradeestavariable(Magaycol.,2009).

Así como existe variabilidad entre razas en cuanto a producción y calidad de la leche, también

existen variaciones entre animales de la misma raza, pudiendo incluso superar estas variaciones a

las interraciales.

3.1.2.Estadoyduracióndelalactación

La producción de leche no es constante a lo largo de toda la lactación. De manera general la

producción aumenta hasta alcanzar el máximo pico de producción, luego desciende a medida que

avanza la lactación. El aumento de la producción de leche hasta el pico de lactación parece ser debi-

do a una mayor capacidad de síntesis de las células epiteliales mamarias, en lugar de un incremento


40

enelnúmerodecélulassecretoras(Capucoycol.,2001;Salama,2005).Posteriormente,eldescenso

progresivo de la producción de leche, tras alcanzar el máximo, es asociado con una reducción en el

contenidodeADNtotaldelparénquimamamario,implicandounadisminuciónenelnúmerodecélu-

lassecretoras(KnightyPeaker,1984;Capucoycol.,2001).

Lamayoríadelascabrassitúansumáximaproducciónentrela3ªy8ªsemanadelactación

(Salama,2005).Así,sehanobtenidovaloresdepicodelactaciónde2,42kgalos45días(Leónycol.,

2012)encabrasMurciano-Granadina,de2,48kgalos45díasencabrasTinerfeñas(Capoteycol.,

2000),ode2,54kgalos54díasencrucedeToggenburgconrazaslocalesdeMéxico(Montaldoycol.,

1997).DeacuerdoalDepartamentodeAgriculturadeEstadosUnidos,losmáximosvaloresdeproduc-

ciónalcanzadosparacabrasmultíparassonde4,63kgalos50díasenSaanen,4,49kgalos40días

enAlpina,yde3,67kgalos45díasenOberhasli(AnimalImprovementProgramsLaboratory,2004).

En lo que respecta a la composición, el contenido de grasa sigue una evolución opuesta

a la evolución de la producción de leche, es decir, una rápida disminución en el transcurso de las

primeras semanas de lactación, a la que sigue un mínimo que se alcanza aproximadamente entre el

finaldel2ºyel6ºmesdelactación,yposteriormente,unaumentolentoyprogresivo(Peris,1994).Sin

embargo, algunos autores no consiguieron observar diferencias de este componente entre las fases

delactacióntemprana,mediaotardía(Capoteycol.,2008).Encuantoalaproteína,lamayoríadelos

autores encontraron que permanece casi constante con pequeñas fluctuaciones alrededor de un

valormedio(Peris,1994;Hejtmankovaycol.,2012).Finalmente,laevolucióndelalactosapresenta

un comportamiento inverso al de la grasa, es decir aumentando en la primera parte de la lactación y

disminuyendoenlaúltima(Parkycol.,2007).

3.1.3.Edadynúmerodelactación

Parececlaroquelaproduccióndelecheesmenorencabrasprimíparasqueencabrasmultí-

paras(Goetschycol.,2011).Dehecho,lasúnicasdiferenciassignificativassehanobservadoentrela

primerayelrestodelaslactaciones(ZengyEscobar,1995).Ellopuededeberseaqueentrelaprimera

y segunda lactación los animales manifiestan una importante diferencia en el desarrollo corporal,

más acentuada en cabras que se cubren precozmente de forma sistemática, como ocurre en las Islas

Canarias(Capoteycol.,2000),Portanto,lascabrasenprimeralactacióntienenmenorvolumende

ubre(Salamaycol.,2004)yportantounamenorcantidaddelechesecretadaporunidaddevolumen

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41

encomparaciónconlascabrasmultíparas(KnightyWilde,1993).Deestaforma,Zahraddeenycol.

(2009)encontraronunincrementoprogresivoenelrendimientolecheroentrela1ªy3ªlactaciónen

variasrazasdecabrasdedoblepropósito(RedSokoto,SahelyWestAfricanDwarf).Mientrasque

Carnicellaycol.(2008)yMiocycol.(2008)encontraronunaumentoenlaproduccióndelechecasi

constantedesdela1ªhastala4ªlactaciónencabrasMaltesa,SaanenyAlpina.

En cuanto a los componentes de la leche considerados de forma porcentual, algunos trabajos

recientes señalaron que las concentraciones de grasa y proteína fueron similares entre los cinco pri-

merospartos,perofuemenorenla6ªlactación(Zengycol.,2008),mientrasqueotrosestudioshabían

observado previamente un incremento de la cantidad de grasa al mismo tiempo que el contenido de

proteínadisminuíaalaumentarelnúmerodelactaciones(Morand-Fehrycol.,1986).

3.1.4.Prolificidad

La producción de leche de cabra puede verse influenciada por el tamaño de la camada (Figura

15).Delgado-Pertiñezycol.(2009)observaronunamayorcantidaddelecheproducidaencabrasde

razaPayoyacondoscabritosrespectoalasdeuno,durantelasprimeras5semanasdespuésdelpar-

to,conindependenciadelossistemasdelactanciaydeordeño.Sinembargoapartirdelasemana6

hastala30,lasproduccionesfueronsimilares.Portanto,elhechodequelascabrasconmásdedos

crías liberen cantidades superiores de lactógeno placentario durante la gestación, parece tener un

mayor impacto sobre la posterior producción de leche, que las diferencias producidas por la estimu-

lacióndeloscabritosallactar(Goetschycol.,2011).

Figura15.CabraMajoreraconuna(izquierda)odos(derecha)crías.(U.D.ProducciónAnimalULPGC).


42

En lo referente a la composición de la leche, algunos estudios observaron que la prolificidad

influíasobreelporcentajedeproteína,sibiennohabíaningúnefectosobre lagrasa(Perisycol.,

1997).Sinembargo,enotrosexperimentosencontraronquelascabrasqueteníandoscabritos,inde-

pendientemente de su origen genético, presentaban una mayor concentración de grasa, proteína y

lactosa(Zygoyiannis,1994).

3.1.5.Estadosanitario

Existen numerosos estudios que han demostrado que los procesos infecciosos en cabras pro-

vocan una disminución en la producción de leche, con un incremento en el RCS que afecta a la vida

mediadelalechedestinadaalconsumidor(ZengyEscobar,1995;Huijpsycol.,2008).Hayquetener

en cuenta que durante la lactación ocurren cambios en el rendimiento lechero relacionados con

procesos no infecciosos, los cuales pueden resultar en un efecto de concentración de las células

somáticas(Paapeycol.,2007;Goetschycol.,2011).Portanto,elaumentobruscodelRCSalfinaldela

lactación donde se produce un descenso en el rendimiento lechero, puede ser resultado de una ma-

yor transferencia de células de origen sanguíneo a la leche, debido a una mayor actividad de factores

relacionadosconlainvolucióndelaglándulamamaria(Manlongatycol.,1998).

3.2. Factores extrínsecos

3.2.1.Alimentación

La alimentación del ganado caprino no sólo influye en la cantidad de leche sino también en la

calidaddelamismayporendeenladelqueso(Pulinaycol.,2008).Debidoalaimportanciadeeste

factor(Figura16),sonnumerososlostrabajosyrevisionesbibliográficasrealizadasatalefecto(Min

ycol.,2005;Álvarezycol.,2007).Además,buenapartedeellosestándedicadosalabúsquedadeali-

mentosalternativos,engeneralsubproductosdelaindustriaalimentaria(Azzazycol.,2012;Romero-

Huelvaycol.,2012).

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43

Figura16.CabrasPalmerasrecibiendounaracióndeconcentradoduranteelordeño.(ICIA).

Entre los componentes de la leche, la grasa es el más sensible a los cambios nutricionales

del animal, siendo la fuente de forraje y los suplementos grasos los que afectan en mayor medida su

cantidadysobretodosucalidad(SanzSampelayoycol.,2007).Elrangodevariacióndelaproteína

es más pequeño que el de grasa, sin embargo, parte de los estudios están enfocados en suplementos

que puedan variar el contenido de αS1-caseína(Valentiycol.,2012).

MuchaszonasdeCanariasnotienensuficientesrecursosparaelpasturajedelosanimales,

lo cual ha ocasionado que las cabras en sistemas intensivos tengan raciones más ricas en alimentos

concentrados y con menos porcentaje de fibra. Estas dietas afectan significativamente el contenido

de grasa en la leche, además de causar muchos problemas de salud en el animal (Álvarez y col.,

2007).Dichoproblemanoes fácilde resolversimplementecon la importaciónde forrajes,por los

elevados costes de transporte, que perjudicaría directamente a los cabreros.

3.2.2.Sistemadeproducción

Debido a que la dieta afecta la composición de la leche de cabra, los sistemas de producción

afectan directamente estos parámetros, ya que los extensivos están basados en el pastoreo y ra-

moneo(Figura17),mientrasquelosintensivosenlautilizacióndepiensosyconcentrados.Incluso,

existendiferenciasdentrodelosmismossistemasproductivos.Porejemplo,cuandosecompararon


44

tres sistemas de producción caprina basados en pastos naturales de llanura, colinas y montaña, la

producción de leche resultó ligeramente inferior en los pastos de montaña, pero su contenido de gra-

sa y proteína, así como los porcentajes de ácidos grasos poliinsaturados fueron mayores respecto a

losotrosdossistemasdemanejo(Morand-Fehrycol.,2007).

Figura17.CabrasdepastoreoenlaisladeLaPalma.(ICIA).

El tipo de especies forrajeras y de concentrados suministrados en la alimentación, también

afectalacalidaddelosquesos.Soryalycol.(2004)observaronunapuntuaciónmayorenelsaborde

los quesos elaborados con leche de cabras que pastaban sin concentrado suplementario en compa-

ración con aquellas que estaban confinadas y cuya dieta estaba basada en concentrados comercia-

les y heno de alfalfa.

En Canarias generalmente las cabras son explotadas en sistemas semi-extensivos, ya que el

pastoreo forma parte importante de la ganadería tradicional. Algunos autores han señalado que al

realizarse de forma controlada contribuye a la biodiversidad y al desarrollo sostenible de la región

(Mataycol.,2010).

3.2.3.Factoresclimáticos

Se ha señalado que las altas temperaturas, la incidencia de radiación solar y una humedad

elevada, son factores condicionantes sobre los animales que afectan su nivel de producción (Sila-

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45

nikove,2000a).Sinembargo,estosfactoresnoafectandeigualmaneraalasdistintasrazas,yaque

por ejemplo, las cabras de zonas templadas de Europa se ven más perjudicadas por las altas tem-

peraturasquelascabrasautóctonasdezonascálidasdeAsia,ÁfricayAméricadelSur(Gaughany

col.,2009).

Porotrolado,aunquelaaltaproducciónlecheraestárelacionadaconlosrecursoshídricos

disponiblesen lazona(Silanikove,2000b),cabedestacarque lascabrasestánmejoradaptadas

quelasvacasyovejasaloslargosperíodosdesequíayalaszonasáridas(Figura18), llegando

inclusoaproducir2litrosdelechealdíaconrestriccióndeaguasisealimentanadecuadamente

(Maltzycol.,1982).

Figura18.CabrasderazaMajoreraenlaisladeFuerteventura.(ICIA).

3.2.4.Condicionesdeordeño

Aunqueelordeñomecánicoestábastantegeneralizadoen lospaíses industrializados,aún

existen muchas regiones donde el ordeño manual es frecuente. Existen pocos trabajos que comparen

la producción y composición de la leche entre ambos métodos de ordeño. Aunque la estimulación

manual mejora el vaciado de la ubre respecto al ordeño a máquina, no debería haber diferencias en

cuantoalaproducciónsiempreycuandoambosmétodosserealicenadecuadamente(Bruckmaier

yBlum,1998).EnloreferentealRCS,algunosautoresnohanconseguidodiferenciassignificativas

entre el ordeño manual y el mecánico, aunque si un mayor recuento de bacterias en la leche del orde-


46

ñomanual(ZengyEscobar,1996).Sinembargo,otrosafirmanqueexisteunaimportantevariabilidad

en el RCS, en lo referente al método de ordeño utilizado, con mayores recuentos durante el ordeño

manual(Haenlein,2002).

Porotrolado,losparámetrosyajustesenlamáquinadeordeñoinfluyenconsiderablemente

sobre la extracción de leche, tanto en términos de cantidad como de calidad. Así por ejemplo, se ha

reportado que las condiciones óptimas de ordeño en cabras griegas se dan con una frecuencia de

pulsaciónde70-90pulsos/min,unapresióndesucciónentre36-44kPayunarelacióndepulsaciónde

65:35(Sinapisycol.,2000).EnrazasAlpinaySaanen,unaaltafrecuenciaenlaordeñadora(90y120

pulsos/minyunarelacióndepulsaciónde60:40)reduceeltiempodeordeño,mientrasquelabajafre-

cuencia(60pulsos/minyunarelacióndepulsaciónde50:50)alargaeltiempodeordeñoydisminuye

elflujodeleche(Billonycol.,2005).Además,sielniveldevacíoesmuyalto,seproduceunestrangu-

lamiento de los pezones en las pezoneras disminuyendo el caudal de leche extraída y puede incidir

en la aparición de mastitis, pero si el vacío es muy bajo, es muy frecuente la caída de las pezoneras

ya que no succionan adecuadamente a los pezones de las cabras y por tanto retrasa el tiempo de

ordeño(MarnetyMcKusick,2001).

Cuando empezaron a implantarse las maquinarias de ordeño en las Islas Canarias, los ga-

naderos se quejaban de que esta práctica producía mastitis a las cabras. Sin embargo, las razones

principales eran que no se manejaban unas adecuadas condiciones higiénicas, además de que las

marcas proveedoras no se habían adaptado a las necesidades de esta especie, tanto en parámetros

como en materiales. Hoy en día los ganaderos conocen la importancia de la máquina de ordeño, re-

presentadoungraveproblemasiéstasufrealgúndesperfectoodaño(Capoteycol.,2010).

En lo referente a la frecuencia de ordeño, en países como Francia, Suiza y Alemania que cuen-

tan con una explotación caprina tecnificada, es habitual realizar dos ordeños al día, cuya eficacia

está respaldada por numerosos estudios que otorgan un elevado incremento de las producciones le-

cheras. Así, en razas como Alpina y Saanen, las diferencias a favor del doble ordeño oscilaban entre

un26y45%(MocquotyAuran,1974;WildeyKnight,1990),aunqueentrabajosmásrecientesdichas

diferenciasestánalrededordel16%(Komaraycol.,2009).

La totalidad de las ganaderías caprinas del Archipiélago Canario realizan un solo ordeño dia-

rio. Este hábito se vio favorecido por la costumbre de elaborar el queso justo después de haber or-

deñado, debido a la imposibilidad de conservar la leche, lo cual implicaba una tarea exigente y difícil

de realizar dos veces al día, y más si consideramos las grandes distancias que recorrían los cabreros

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47

enlabúsquedadezonasdepastoreo.Sinembargo,lasmejorastecnológicasproducidasenelsector

caprinoenlosúltimosañosconlaproliferacióndemaquinariadeordeño,tanquesderefrigeracióne

industrias con circuito de recogida de la leche, suponía que la variación en la frecuencia de ordeño

permitiría aumentar los rendimientos de los rebaños, pero los primeros estudios realizados en cabras

Tinerfeñasconsiguieronincrementosentresóloel6y8%(Capoteycol.,2000).

4. Estructura anatómica y conformación de la glándula mamaria

4.1. Anatomía de la glándula mamaria caprinaLa ubre caprina, conformada por dos glándulas independientes, está situada en la región

inguinal cubriendo la cara interna de los muslos y con una proyección desde atrás hacia adelante.

Cada glándula mamaria está compuesta por una cisterna y una papila o pezón, y se separa de la

otra por un surco intermamario. En las cabras, al igual que en el resto de las hembras con aptitud

lechera, el desarrollo mamario constituye la base donde podrá proliferar el tejido secretor (Knight

yPeaker,1982).

Cada complejo mamario se compone de diversos elementos funcionales responsables del

procesobiosintético,almacenamientoytransportedelaleche(Figura19):

Figura19.Vistalateralglándulamamariacaprina.A:parénquimamamario;b:porcióncisternaldelsenolactífero;c:por-ciónpapilardelsenolactífero;d:papilamamaria;e:nóduloslinfáticosmamarios;f:conductoyorificiopapilar;g:con-

ductoslactíferoscolectores.(Sandoval,2003).


48

4.1.1.Parénquimaglandular

En el parénquima glandular o tejido noble se encuentran las unidades secretoras, o alvéolos,

que presentan como característica primordial la presencia de un epitelio secretor que delimita inter-

namente el lumen donde se deposita la leche secretada por la células. Exteriormente cada alvéolo

presenta una compleja red de capilares arteriales y venosos que están en íntimo y estrecho contacto

conelepiteliobasal (ConstantinescuyConstantinescu,2010).Losalvéolosagrupadosenracimos,

lobulillos y lóbulos, son vaciados por pequeños canalículos que confluyen para formar conductos de

mayor tamaño, llamados canales galactóforos, los que a su vez convergen en estructuras de mayor

diámetrointerno,conlímitesmásdifusosdenominadoscisternasdelamama(FerrandoyBoza,1990).

Finalmente este sistema de conducción se comunica con una cisterna del pezón, ubicada en

esteúltimoycuyovolumenvaríasegúneltamañodelpezón.Elinteriordelapapilamamariapresenta

una mucosa muy plegada para evitar el flujo espontáneo de leche al exterior así como la penetración

de agentes patógenos, y una concentración de fibras musculares que contienen numerosas termina-

cionesnerviosasyvasossanguíneos(Suárez-Trujilloycol.,2013).

Otroelementoanatómicofuncionaldeimportancia loconstituyenlascélulasmioepiteliales

que envuelven externamente a los alveolos y que por ser fibras musculares lisas responden activa-

mente a las descargas de oxitocina, permitiendo un correcto vaciamiento de la leche acumulada en

lasestructurasnocisternales(BruckmaieryBlum,1998).

4.1.2.Sistemasuspensorio

El aparato suspensorio de la ubre lo conforma una red de fibras de naturaleza elástica y fi-

brosa, procedentes de la pared ventral del abdomen, que penetran en el parénquima mamario a di-

ferentes niveles, evitando que los cuerpos glandulares graviten directamente sobre la piel que los

envuelve(Suárez-Trujilloycol.,2013).Laproporcióndetejidoglandularydetejidodesosténpresenta

una buena caracterización de una glándula mamaria en cuanto a su mayor o menor capacidad pro-

ductiva. Así una glándula con una gran cantidad de tejido de sostén presentará un aspecto exterior

con escasa variación antes o después del ordeño, mientras que una glándula rica en tejido noble

presentaráunaspectomuyretraídodespuésdelordeño(FerrandoyBoza,1990).

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4.1.3.Sistemacirculatorioylinfático

Parapodersintetizarlaleche,debecircularporlaubreunaenormecantidaddesangre,ya

que se requiere una elevada proporción de nutrientes para que las células secretoras la produzcan.

Así mismo, las células alveolares requieren tiempo para la captura de estos nutrientes, por lo que un

pasodesangreaaltavelocidadnoresolveríaelproblema.Paraquelasecreciónlácteasellevea

cabo eficientemente, el aporte sanguíneo se ralentiza a nivel alveolar como consecuencia del enor-

me desarrollo del sistema venoso de la ubre, encontrándose alrededor de las mamas, ricas redes

capilares conectadas con amplios plexos venosos por los que la sangre circula muy lentamente (Fe-

rrandoyBoza,1990).

También cabe destacar la existencia de una gran representación linfática, destacando los

ganglioslinfáticosmamariosqueactúancomolinfocentros,yquedesempeñanunimportantepapel

como barrera defensiva frente a las infecciones que puedan afectar a la ubre (Constantinescu y

Constantinescu,2010).

4.2. Morfología de la ubre de las razas canariasLa morfología de la ubre es un importante parámetro en la ganadería caprina por su contribu-

ción en la producción de leche y la aptitud de ésta para el ordeño mecanizado. Los parámetros más

utilizados en la definición de la morfología de la ubre son: profundidad y volumen de la ubre, morfolo-

gía del pezón (longitud, anchura, ángulo de implantación y situación antero-posterior), y altura de las

cisternasmamarias(Figura20).

Una morfología de ubre adecuada es muy importante para una buena adaptación del animal

a la máquina de ordeño, ya que puede evitar algunos efectos indeseables, como por ejemplo la in-

hibición del reflejo de eyección láctea, o la caída de pezoneras que conllevaría un mayor tiempo de

ordeño(Barillet,2007).Peris(1994)alestudiar laaptitudalordeñomecánicodecabrasMurciano-

Granadina,describióqueexisteunagranheterogeneidadenloscriteriosmetodológicosylasmedi-

das morfológicas evaluadas, así como en el estado de lactación utilizado por cada autor para evaluar

la aptitud al ordeño.


50

Figura20.Medidasmorfológicadelaubre.DEP:distanciaentrepezones;ACS:alturacisterna-suelo;APS:alturapezón-suelo;AIUS:alturainserción-suelo;PU:profundidadubre.(U.D.ProducciónAnimalULPGC).

La morfología de la ubre ha sido descrita en las principales razas lecheras: Saanen y Alpina

(Manfrediycol.,2001),Toggenburg(Wang,1989),Murciano-Granadina(Perisycol.,1999).Enlostra-

bajos se describen distintas formas de ubres: redondeadas o globosas, ovales, piriformes, pendulares

o planas. También diferentes tipos de pezón: cónicos, cilíndricos, en forma de botella o bulbosos,

pequeños, o voluminosos. En el caso de la razas canarias, la ubre se caracteriza porque la altura del

pezónesmayorquelaalturadelfondodecisternaenungrannúmerodeanimales(Figura21),una

circunstancia negativa en el momento del ordeño, ya que es necesaria la intervención manual para

levantar la ubre y extraer la porción de leche que hay debajo del pezón, lo cual incrementa el tiempo

deordeño(Capoteycol.,2008).

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51

Figura21.Típicaubredelascabrascanarias.(U.D.ProducciónAnimalULPGC).

Algunos autores han señalado que la selección genética para mejorar la producción lechera

llevadaacaboenlasúltimasdécadas,haproducidoefectosindeseablesenlamorfologíamamaria,

como la tendencia de que las ubres tengan ubicados los pezones más horizontalmente para incre-

mentar la capacidad cisternal pero que trae como consecuencia una menor ordeñabilidad de los

animales(MarnetyMcKusick,2001;Barillet,2007).

5. Fisiología de ordeñoEl inicio masivo de la secreción láctea corresponde al momento del parto en que se produce

un cambio hormonal importante, con el descenso en el nivel de la progesterona y un incremento de

estrógenos,prolactina,yglucocorticoides(Davisycol.,1979).Lalactogénesiscomprendelasíntesis

intracelular de la leche y su posterior transferencia desde el citoplasma hacia el lumen alveolar. El

componente de base del tejido secretor es el alvéolo, envuelto por una capa de células mioepiteliales

que ayudan en la contracción de los alvéolos por efecto de la oxitocina, produciendo la expulsión de

la leche hacia los conductos galactóforos. Este proceso neurohormonal es provocado por estímulos

comoelamamantamientodelacríaoelprocesodeordeño(ParkyHaenlein,2010).

Las terminaciones nerviosas del pezón están conectadas con el sistema nervioso central y

el hipotálamo a través de las raíces dorsales de los nervios lumbares de la médula espinal. Cuando

un estímulo alcanza el sistema nervioso central provoca que el lóbulo posterior de la hipófisis libere


52

oxitocina. La oxitocina viaja a través del flujo de sangre hasta la glándula mamaria, donde causa la

contraccióndelascélulasmioepiteliales(Figura22)(BruckmaieryBlum,1998).

Figura22.Esquemadeeyeccióndelecheencabras.(Caja,2003).

5.1. Efectos de la oxitocina sobre la eyección de lecheLa oxitocina es un neuropéptido responsable de la eyección de la leche, con el consecuente

vaciado de la ubre. Dependiendo del grado de estimulación de la glándula mamaria, se producen

diferentes respuestas en la liberación de oxitocina. De esta forma, el amamantamiento de la cría es

un estímulo más potente que el ordeño, mientras que el ordeño manual induce una liberación más

pronunciadadeoxitocinaqueelordeñoamáquina(BruckmaieryBlum,1998).Además, laestimu-

lación previa al ordeño es importante en algunas especies como el ganado bovino porque aumenta

los niveles de oxitocina y promueve la inducción temprana de eyección de la leche para evitar una

interrupción del flujo de leche durante el ordeño, sin embargo en cabras no es tan importante esta

estimulación previa por el gran volumen de leche almacenado en la cisterna, y que está disponible en

elmomentodelordeño(BruckmaieryWellnitz,2008).

El proceso de eyección de leche en cabras, en respuesta a la oxitocina, es similar al de vacas

yovejas,perolaextraccióndelalecheesdiferentedebidoalamorfologíadelaubre(Bruckmaiery

Blum,1998).Encabras,laliberacióndeoxitocinaesaltamentevariableenelmismoanimalyentre

diferentes individuos de la misma raza, siendo fácilmente inducida por estimulación táctil previa o por

lamáquinadeordeño(BruckmaieryBlum,1998;MarnetyMcKusick,2001).

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5.2. Efectos de la administración de oxitocina exógena sobre la producción de lecheAunque existen numerosos informes de que la administración exógena de oxitocina en el mo-

mento del ordeño puede aumentar la producción de leche, hay contradicciones en la literatura con

respecto a sus efectos sobre el rendimiento lechero y calidad de la leche. Éstos se deben principal-

menteadiferenciasenlametodologíaydiseñoexperimental,quevandesdeelnúmerodeanimales

utilizados, estado de lactación, inyección seguida de remoción de leche o no, inyección administrada

conlasubresllenasovacías,ydosisdeoxitocinaadministrada(Lollivierycol.,2002).

Laadministracióndedosisintravenosasentre0,1y1UIdeoxitocinapuedeinducirlabajadade

la leche en cabras, ya que sólo es necesario rebasar un umbral mínimo de concentración de oxitocina

parainiciarelproceso(Schamsycol.,1984).Sinembargo,enlamayoríadelostrabajosexperimentales,

losinvestigadoreshanutilizadodosisconcantidadessuprafisiológicas(Lollivierycol.,2002).

En vacas, se ha reportado que la administración exógena de oxitocina es una terapia eficaz

contralamastitis(Macuhovaycol.,2004).Sinembargonosehanencontradocambiosaparentesen

el sistema inmune por los tratamientos con oxitocina, aunque las inyecciones en cantidades supra-

fisiológicas pueden ayudar en la eliminación de microorganismos patógenos debido a un completo

vaciadodelaubre(Werner-Misofycol.,2007).Adicionalmente,algunosestudiosconfirmanunare-

ducción en la eyección espontanea de leche después de retirar los tratamientos crónicos de oxito-

cina, lo cual puede deberse a una disminución de la oxitocina liberada desde la hipófisis, o por una

reducción en la contractibilidad de las células mioepiteliales a niveles fisiológicos de oxitocina en

sangre(Bruckmaier,2003).

6. Fraccionamiento lechero

En el instante del ordeño, se considera que la leche se encuentra almacenada en la ubre en

dos niveles bien diferenciados (fracciones de ubre), o como se obtiene durante una rutina de ordeño

completa (fracciones de ordeño).


54

6.1. Fracciones de ubre

6.1.1.Lechecisternal

Cierta cantidad de leche está contenida en la cisterna o seno glandular. La especial es-

tructuración anatómica de la glándula mamaria del caprino, que incluye la presencia de grandes

cisternas(Figura23),permitequebuenapartedelcontenidodelechealmacenadaenelinteriorde

laglándulapuedaserevacuadaenformapasiva,esdecir,sinunprocesodecontracción(Bruck-

maieryBlum,1998).

Figura23.Laubrecaprinacanariadestacaporsusgrandescisternas.(U.D.ProducciónAnimalULPGC).

6.1.2.Lechealveolar

Una parte de la leche se acumula en los alvéolos y en la red de canales y conductos (Figu-

ra24),yestáfijadaporfuerzascapilares.Parasuobtenciónseprecisadelaparticipaciónactiva

delanimal,atravésdelapuestaenmarchadelmecanismodeeyeccióndeleche(Bruckmaiery

Wellnitz,2008).

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55

Figura24.Representacióndelaexpulsióndelalechecontenidaenlosalveolos.(Schmidt,1971).

El reparto entre la leche cisternal y alveolar se determinaba mediante el uso de una cánula que

seintroducíaporelesfínterdelpezónypermitíaeldrenajedelalechecisternal(PeakeryBlatchford,

1988).Noobstante,estatécnicapuedesobreestimarelvolumendelechecisternal,yaquealgunas

razas son muy sensibles a la liberación espontánea de oxitocina endógena, como consecuencia de

reflejoscondicionadosalordeñoocomoresultadodelamanipulacióndelpezón.Porello,lasnuevas

técnicas incluyen el uso de un antagonista de los receptores de oxitocina para bloquear la eyección

espontáneadeleche(Wellnitzycol.,1999).

6.2. Fracciones de ordeño

6.2.1.Lechedemáquina

El fraccionamiento obtenido durante el ordeño mecánico permite diferenciar una porción de

leche recogida desde la colocación de las pezoneras hasta el cese de flujo de leche sin intervención

algunaporpartedelordeñador(Figura25).

6.2.2.Lechedeapuradoamáquina

La morfología de ubre de muchas razas caprinas hace necesario realizar un masaje de las

regiones cisternales y alzar el ligamento suspensorio por parte del ordeñador, antes de la retirada de

laspezoneras,parafavorecerlaremocióndelalechecontenidadebajodelospezones(Figura25).


56

6.2.3.Lecheresidual

La leche total contenida en la glándula mamaria difícilmente se puede extraer en su totalidad

por medios mecánicos o manuales, puesto que una parte sólo puede ser extraída por mecanismos

hormonales. Así pues, mediante una inyección de oxitocina se extrae la fracción retenida en el tejido

mamario, y aunque no se considera propiamente como una fracción de ordeño, permite expresar el

grado de vaciado de la ubre conseguido por medio del ordeño mecánico.

Figura25.Fraccióndelechedemáquina(izquierda)ydeapuradoamáquina(derecha).(ICIA).

Porconsiguiente,lascabrasconmejoradaptaciónalamáquinadeordeñoseránaquellasque

presenten una mayor cantidad de leche de máquina, y menor volumen de leche de apurado y residual,

lo que implica una reducción en el tiempo dedicado al ordeño. Sin embargo, en las explotaciones

ganaderas,hayunatendenciacentradaenreducirelnúmerodeoperacionesduranteelordeño,omi-

tiendoelapuradoamáquina(McKusickycol.,2003).

Porotrolado,sehaseñaladolaimportanciadelamorfologíadeubresobrelasfraccionesde

ordeño, destacando la red canalicular, la altura de las cisternas mamarias y el ángulo de inclinación

delospezones(LeDu,1985),habiéndoseresaltadotambiénquelasubresglobosassonmásfáciles

deordeñarquelasubresdescendidas(Capoteycol.,2006).Además,lafrecuenciadeordeñoafecta

especialmente la fracción de apurado a máquina, donde el doble ordeño incrementa significativa-

INTRODUCCIÓN

57

mente los porcentajes en las cabras Tinerfeñas, debido al hecho de tener que realizar esta labor dos

vecesparauncorrectovaciadodelaubre(Capoteycol.,2009).

Deformageneral,losvaloresderepartodelecheduranteelordeñoencaprinosesitúanen-

tre61a90%paralechedemáquina,10a23%paralechedeapuradoamáquinayun10a17%para

lalecheresidual(Capoteycol.,2000).Porotraparte,lafraccióndelechedemáquinaeslaquemás

disminuye a lo largo de la lactación, siguiendo una evolución paralela a la leche total ordeñada, e

inversa al de la leche de apurado a máquina, en donde la leche residual permanece más o menos es-

table,peroexistiendounaaltavariabilidadentreindividuos(PeakeryBlatchford,1988;Capoteycol.,

2008).Díazycol(2013)estudiaronlosnivelesdecortisolsobreelfraccionamientolecheroencabras

Murciano-Granadinaynoencontraroncorrelaciónentreéstosconelvolumendelechedeapuradoa

máquina y el tiempo total de ordeño, por lo que las variaciones de esta hormona pueden estar asocia-

das a factores fisiológicos en el animal y no necesariamente al estrés. En general, estas fracciones

tienden a mantener un volumen constante a medida que los animales se adaptan a la máquina de

ordeño(Rovai,2001).

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J. Dairy Sci. 96 :1071–1074http://dx.doi.org/ 10.3168/jds.2012-5435 © American Dairy Science Association®, 2013 .

ABSTRACT

Thirty-six dairy goats of 3 breeds (Majorera, Tiner-feña, and Palmera) in mid lactation (124 ± 8 d in milk) were subjected unilaterally to once (×1) or twice daily milking (×2) for 5 wk to evaluate udder morphology, milk partitioning, and somatic cell count. Majorera and Palmera goats presented the highest and lowest udder depth values, respectively, whereas the differences be-tween initial and final cistern-floor and teat-floor dis-tances were not affected by milking frequency or breed factors. Cisternal and alveolar milk percentages were similar between ×1 and ×2 in the studied breeds. Milk-ing frequency did not affect milk composition in the cisternal fraction, suggesting a greater transfer of milk from the alveoli to the cistern during early udder filling. However, milking frequency caused diverse changes in the milk composition in the alveolar fraction, especially in fat, lactose, and total solids contents. No udder halves presented clinical mastitis during the experimental pe-riod, suggesting that ×1 does not impair udder health and indicating that the studied breeds are adapted to this milking frequency. Key words: milking frequency , milk partitioning , milk quality , dairy goat

Short Communication

Intramammary filling rate and cisternal capacity to store milk determine the choice of an adequate milking routine. Overfilling of the udder increases intramam-mary pressure and distention of the alveoli, which can compromise subsequent milk synthesis as has been reported by Peaker (1980). Animals with large cisterns are milked faster with simplified routines and are better at tolerating extended milking intervals (Knight and Dewhurst, 1994; Ayadi et al., 2003; Salama et al., 2003).

Techniques for determining cisternal and alveolar milk fractions have been improved and include the

use of an oxytocin receptor antagonist to block spon-taneous milk ejection (Wellnitz et al., 1999), allowing a reliable separation between both fractions. This is important because the udder morphology of some dairy goat breeds (e.g., Tinerfeña breed) is characterized by higher teat-floor distance (TF) than cistern-floor distance (CF), a negative circumstance that makes more difficult the emptying of cisternal milk by gravity (López et al., 1999).

The aim of the present study was to determine the effects of milking frequency on udder morphology, milk partitioning, composition of each fraction, and SCC of 3 dairy goat breeds (Majorera, Tinerfeña, and Palmera).

The present study was performed on the experimental farm of the Instituto Canario de Investigaciones Agrar-ias in Tenerife (Spain) on 36 dairy goats belonging to 3 different breeds: Majorera (n = 12), Tinerfeña (n = 12), and Palmera (n = 12). The experimental animal procedures were approved by the Ethical Committee of the Universidad de Las Palmas de Gran Canaria (Aru-cas, Spain). Goats with symmetrical udder halves were in third parity with 124 ± 8 DIM at the beginning of the experiment. The milking frequency before the start of the experimental period was once per day. During a 5-wk period, each goat was milked once daily in the left mammary gland (×1; at 0700 h), whereas the right mammary gland was milked twice daily (×2; at 0700 and 1700 h). The animals were fed with commercial concentrate, maize, lucerne, wheat straw, and a vita-min-mineral corrector in accordance with the guidelines issued for lactating goats by Institut National de la Recherche Agronomique (INRA, Paris, France; Jarrige, 1990). Goats were milked in a double 12-stall parallel milking parlor (Alfa Laval Iberia SA, Madrid, Spain) equipped with recording jars (4 L ± 5%) and a low-line milk pipeline. Milking was performed at a vacuum pres-sure of 42 kPa, a pulsation rate of 90 pulses/min, and a pulsation ratio of 60/40, in accordance with Capote et al. (2006). The milking routine included wiping dirt off teat ends and stripping 2 to 3 squirts of milk from each teat; machine milking and stripping milking, done by the operator to remove the milk remaining in the udder before cluster removal; and teat dipping in an

Short communication: Effects of milking frequency on udder morphology, milk partitioning, and milk quality in 3 dairy goat breeds A. Torres ,* N. Castro ,† L. E. Hernández-Castellano ,† A. Argüello ,†1 and J. Capote * * Instituto Canario de Investigaciones Agrarias, La Laguna, Tenerife 38200, Spain † Department of Animal Science, Universidad de Las Palmas de Gran Canaria, 35413 Arucas, Spain

Received February 15, 2012. Accepted October 26, 2012. 1 Corresponding author: [email protected]


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iodine solution (P3-cide plus; Henkel Hygiene, Barce-lona, Spain).

Milk recording and sampling were done at wk 1, 3, and 5. Before the experiment, the goats were exposed to 3 wk of adaptation. In the first and second weeks, the goats began to enter the milking parlor in the af-ternoon, but the goats were not milked. During the third week of adaptation, the goats were milked once and twice daily in the left and right mammary gland, respectively, but the milk was not collected. Udder measurements of each goat were taken just before the first and the last milking of the experimental period. The following udder measurements were performed: CF and TF, recorded as the differences between initial and final measurements (ΔCF and ΔTF), and ud-der depth (UD), recorded as the difference in distance between the udder floor and the cistern floor.

Before the a.m. milking (24- and 14-h milking inter-vals for ×1 and ×2, respectively) on the sampling days, each goat was injected intravenously with 0.8 mg of an oxytocin receptor blocking agent (Tractocile; Ferring SAU, Madrid, Spain) inside a pen immediately before entering the parlor to record cisternal milk volume. After cisternal milk removal, the goats were injected intravenously with 2 IU of oxytocin (Oxiton; Laborato-rios Ovejero, León, Spain) to reestablish milk ejection to allow the measurement of alveolar milk. Cisternal and alveolar milk volumes were recorded by using the recording jars in the milking parlor and milk samples were collected separately for each udder half and frac-tion.

Milk samples (cisternal and alveolar fractions) were analyzed immediately after collection to determine milk composition and SCC. Protein, fat, lactose, TS, and SNF percentages were determined using a MilkoScan 133 analyzer (Foss Electric A/S, Hillerød, Denmark), and SCC using a Fossomatic 90 cell counter (Foss Electric A/S). Somatic cell count was calculated by a weighted average of the cisternal and alveolar SCC.

The statistical analysis used to evaluate the effects of breed and milking frequency on morphological param-eters of udder, milk partitioning and SCC was PROC MIXED of SAS (version 9.0; SAS Institute Inc., Cary, NC). The model included fixed effects of milking fre-quency (×1 or ×2) and breed (Majorera, Tinerfeña, or Palmera) and their interactions. The repeated state-ment was used to take into account repeated measures for each individual animal. Differences among the breeds and milking frequencies were evaluated using a multiple comparison test following the Tukey-Kramer method. Statistical differences were considered signifi-cant at P < 0.05. Data are presented as least squares means.

The ΔCF and ΔTF (Table 1) did not differ due to milking frequency or breed (P > 0.05). Knight and Dewhurst (1994) found that large cisternal size may explain the small negative effects of longer milking intervals on udder morphology because it is better pre-pared to accommodate greater milk accumulation, and may explain the absence of differences in the cistern descent of goat udders.

Majorera and Palmera goats presented the highest and lowest UD values, respectively (Table 1). The in-crease in UD values during the experimental period can be explained because ΔTF were lower than ΔCF, which implies that increasing the cistern depth increases the UD. The cistern depth is a consequence of teat place-ment of the studied goats whose teats are not located in the ventral portion of the udder (Capote et al., 2006).

Cisternal and alveolar milk percentages were similar between ×1 (24 h after milking) and ×2 (14 h after milking) in Majorera, Tinerfeña, and Palmera breeds (Table 1). Salama et al. (2004) did not find differences in cisternal milk fraction in Murciano-Granadina goats between ×1 and ×2 when milking intervals were 16 and 24 h (values ranged from 66 to 76%). The differences observed in the cisternal and alveolar fractions between breeds may be explained by the cisternal size, because greater cisterns are able to store more milk. Bruckmaier et al. (1997) explained that a large absolute cisternal volume implies that a large fraction of the milk is stored within the cisternal cavities and it varies according to breed.

Percentages of cisternal milk components (Table 1) were not affected by milking frequency (P > 0.05). This absence of differences between ×1 and ×2 goats might be due to the fact that approximately 80% of total milk was stored in the cisternal compartment and most of the transfer of milk from the alveoli and small milk ducts had already taken place. However, McKusick et al. (2002) observed marked differences in milk fat percentage in the cisternal fraction between different milking intervals in dairy ewes, in which the cistern was only capable of storing approximately 50% of the total milk volume, being more susceptible to changes in the transfer of milk components.

Alveolar milk of ×1 goats contained higher percent-ages of fat and TS than alveolar milk of ×2 goats, but these differences were significant only in the Majorera breed. McKusick et al. (2002) explained that a transfer of milk fat from the alveoli to the cistern occurs dur-ing early udder filling; however, this transfer no longer takes place during later intervals, resulting in an ac-cumulation of milk fat in the alveolar compartment. Alveolar milk was richer in fat content than cisternal milk in all breeds and milking intervals, which agrees

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with observations in dairy cows by Waldmann et al. (1999) and dairy ewes by McKusick et al. (2002).

Milk protein percentage was unaffected by milk par-titioning (Table 1). This agrees with observations in dairy ewes by McKusick et al. (2002) and dairy cows by Ayadi et al. (2004), indicating that casein micelles passed more freely than fat globules from the alveolar to the cisternal compartment between milkings, result-ing in minimal differences in protein concentration of milk fractions.

Lactose content in cisternal milk was not affected by milking frequency (Table 1). Lactose content in alveolar milk in Majorera and Tinerfeña breeds was not different between ×1 and ×2 goats, whereas in the Palmera breed, lactose content was lower for ×1 goats (P < 0.05). The decrease in milk lactose percentage seems to be due to lactose passing from milk into blood through an impaired tight junction (Stelwagen et al., 1994) associated with extended milking intervals.

The results for the SCC showed that Tinerfeña goats presented higher values than Majorera and Palmera goats for ×1. Nevertheless, no differences in SCC level were found for ×2 between the studied breeds (Table 1). Harmon (1994) indicated that variability in SCC within a breed is greater than variability in SCC be-

tween breeds; therefore, it is possible that the results found could be due to an effect of individual variability.

Milking frequency did not affect the milk SCC. No coincident data exist about the effect of milking fre-quency on SCC levels. Salama et al. (2003) did not find significant differences in SCC between ×1 and ×2 goats in 32 Murciano-Granadina goats during an entire lactation, whereas Komara et al. (2009) conducted 2 experiments with Alpine goats and found differences only in experiment 1, which could be due to the dif-ferent number of goats used in each experiment (48 for experiment 1 and 8 for experiment 2) and to individual variability, as indicated by the authors.

No udder halves presented clinical mastitis during the experimental period, suggesting that ×1 does not impair udder health and indicating that the breeds are fully adapted to this milking frequency. Lacy-Hulbert et al. (2005) did not report differences in the number of clinical or subclinical infections between ×1 and ×2 in dairy cows. Nudda et al. (2002) suggested that high SCC levels induced by a change in milking frequency may be temporary and not necessarily due to mam-mary gland infections.

In conclusion, the fact that about 80% of total milk was stored in cisternal compartments for 14- and 24-h

Table 1. Morphological parameters of udder, milk partitioning, milk composition, and SCC of 3 dairy goat breeds milked once (×1) or twice (×2) daily1,2

Parameter3

Goat breed

SEM

P-value4Majorera Tinerfeña Palmera

×1 ×2 ×1 ×2 ×1 ×2 B F B × F

Initial UD (cm) 29.10a 28.10ab 26.65abc 25.55bc 24.80c 25.00c 0.422 0.001 0.41 0.74Final UD (cm) 29.95a 28.80ab 28.60ab 27.10ab 26.30b 25.60b 0.507 0.021 0.26 0.94ΔCF (cm) 0.85 0.70 1.95 1.55 1.50 0.60 0.293 0.40 0.42 0.87ΔTF (cm) 0.25 0.05 1.35 1.10 0.35 0.15 0.227 0.11 0.64 0.999Cisternal milk (%) 81.63a 80.21ab 81.62ab 82.04a 77.78b 78.23b 0.524 0.007 0.86 0.68 Fat (%) 3.70 3.66 3.63 3.47 3.78 3.83 0.049 0.11 0.60 0.66 Protein (%) 3.57bc 3.55bc 3.59abc 3.44c 3.80a 3.68ab 0.040 0.049 0.21 0.76 Lactose (%) 4.92 4.90 4.78 4.78 4.79 4.87 0.023 0.083 0.70 0.64 TS (%) 12.85a 12.80ab 12.73ab 12.39b 13.10a 13.08a 0.073 0.012 0.32 0.58 SNF (%) 9.19a 9.14a 9.07ab 8.92b 9.29a 9.25a 0.038 0.011 0.26 0.79Alveolar milk (%) 18.37b 19.79ab 18.38ab 17.96b 22.22a 21.77a 0.524 0.007 0.86 0.68 Fat (%) 6.03b 4.84d 5.86bc 4.94cd 7.07a 6.45ab 0.166 0.001 0.001 0.66 Protein (%) 3.52 3.54 3.59 3.50 3.69 3.58 0.039 0.51 0.47 0.79 Lactose (%) 4.78ab 4.87a 4.74ab 4.76ab 4.58c 4.70b 0.022 0.001 0.046 0.52 TS (%) 15.03b 13.94c 14.73bc 13.89c 16.05a 15.38ab 0.163 0.001 0.002 0.82 SNF (%) 9.00 9.12 9.00 8.96 8.98 8.99 0.036 0.61 0.71 0.68SCC (log/mL) 6.00b 5.90b 6.33a 6.26ab 6.08b 5.92b 0.051 0.010 0.25 0.93a–dMeans with different superscripts within the same row are different (P < 0.05).1Data are least squares means and standard error of means.2Morphological parameters were recorded before the first and the last milking of the experimental period. Milk parameters were measured at 24- and 14-h milking intervals for ×1 and ×2 goats, respectively.3UD = udder depth; ΔCF = difference between initial and final cistern-floor (CF) distance; ΔTF = difference between initial and final teat-floor (TF) distance.4B = breed; F = milking frequency.


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milking intervals suggested a greater transfer of milk from the alveoli to the cistern during early udder fill-ing and, therefore, did not produce significant changes in the milk composition. However, milking intervals caused diverse changes in the milk composition in the alveolar fraction, especially in fat, lactose, and TS contents; therefore, it merits further investigation of the mechanisms responsible for milk ejection between milkings.

ACKNOWLEDGMENTS

This work was supported by Fondo Europeo de De-sarrollo Regional-Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (FEDER-INIA) RTA2009-00125.

REFERENCES

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Ayadi, M., G. Caja, X. Such, M. Rovai, and E. Albanell. 2004. Effect of different milking intervals on the composition of cisternal and alveolar milk in dairy cows. J. Dairy Res. 71:304–310.

Bruckmaier, R. M., G. Paul, H. Mayer, and D. Schams. 1997. Machine milking of Ostfriesian and Lacaune dairy sheep: Udder anatomy, milk ejection and milking characteristics. J. Dairy Res. 64:163–172.

Capote, J., A. Argüello, N. Castro, J. L. López, and G. Caja. 2006. Correlations between udder morphology, milk yield and milking ability with different milking frequencies in dairy goats. J. Dairy Sci. 89:2076–2079.

Harmon, R. J. 1994. Physiology of mastitis and factors affecting so-matic cell counts. J. Dairy Sci. 77:2103–2112.

Jarrige, J. 1990. Alimentación de bovinos, ovinos y caprinos. 1st ed. Mundi-Prensa, Madrid, Spain.

Knight, C. H., and R. J. Dewhurst. 1994. Once daily milking of dairy cows: Relationship between yield loss and cisternal milk storage. J. Dairy Res. 61:441–449.

Komara, M., M. Boutinaud, H. Ben Chedly, J. Guinard-Flament, and P. G. Marnet. 2009. Once-daily milking effects in high-yielding alpine dairy goats. J. Dairy Sci. 92:5447–5455.

Lacy-Hulbert, S. J., D. E. Dalley, and D. A. Clark. 2005. The effects on once a day milking on mastitis and somatic cell count. Proc. N.Z. Soc. Anim. Prod. 65:137–142.

López, J. L., J. Capote, G. Caja, S. Peris, N. Darmanin, A. Argüello, and X. Such. 1999. Changes in udder morphology as a consequence of different milking frequencies during first and second lactation in Canarian dairy goats. Pages 100–103 in Milking and Milk Produc-tion of Dairy Sheep and Goats. F. Barillet, and N. P. Zervas, ed. Wageningen Pers, Wageningen, the Netherlands.

McKusick, B. C., D. L. Thomas, Y. M. Berger, and P. G. Marnet. 2002. Effect of milking interval on alveolar versus cisternal milk accumulation and milk production and composition in dairy ewes. J. Dairy Sci. 85:2197–2206.

Nudda, A., R. Bencini, S. Mijatovic, and G. Pulina. 2002. The yield and composition of milk in Sarda, Awassi, and Merino sheep milked unilaterally at different frequencies. J. Dairy Sci. 85:2879–2884.

Peaker, M. 1980. The effect of raised intramammary pressure on mam-mary function in the goat in relation to the cessation of lactation. J. Physiol. 301:415–428.

Salama, A. A. K., G. Caja, X. Such, S. Peris, A. Sorensen, and C. H. Knight. 2004. Changes in cisternal udder compartment induced by milking interval in dairy goats milked once or twice daily. J. Dairy Sci. 87:1181–1187.

Salama, A. A. K., X. Such, G. Caja, M. Rovai, R. Casals, E. Albanell, M. P. Marín, and A. Martí. 2003. Effects of once versus twice daily milking throughout lactation on milk yield and milk composition in dairy goats. J. Dairy Sci. 86:1673–1680.

Stelwagen, K., S. R. Davis, V. C. Farr, C. G. Prosser, and R. A. Sher-lock. 1994. Mammary epithelial cell tight junction integrity and mammary blood flow during an extended milking interval in goats. J. Dairy Sci. 77:426–432.

Waldmann, A., E. Ropstad, K. Landsverk, K. Sørensen, L. Sølverød, and E. Dahl. 1999. Level and distribution of progesterone in bo-vine milk in relation to storage in the mammary gland. Anim. Reprod. Sci. 56:79–91.

Wellnitz, O., R. M. Bruckmaier, C. Albrecht, and J. W. Blum. 1999. Atosiban, an oxytocin receptor blocking agent: Pharmacokinet-ics and inhibition of milk ejection in dairy cows. J. Dairy Res. 66:1–8.

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Please cite this article in press as: Torres, A., et al., Comparison between two milk distribu-tion structures in dairy goats milked at different milking frequencies. Small Ruminant Res. (2013),http://dx.doi.org/10.1016/j.smallrumres.2013.04.013

ARTICLE IN PRESSG ModelRUMIN-4519; No. of Pages 6

Small Ruminant Research xxx (2013) xxx–xxx

Contents lists available at SciVerse ScienceDirect

Small Ruminant Research

journa l homepage: www.e lsev ier .com/ locate /smal l rumres

Comparison between two milk distribution structures indairy goats milked at different milking frequencies

A. Torresa, N. Castrob, A. Argüellob, J. Capotea,∗

a Instituto Canario de Investigaciones Agrarias (ICIA), La Laguna 38200, Tenerife, Spainb Department of Animal Science, Universidad de Las Palmas de Gran Canaria, Arucas 35413, Spain

a r t i c l e i n f o

Article history:Received 6 March 2013Received in revised form 26 April 2013Accepted 30 April 2013Available online xxx

Keywords:Milk yieldMilk partitioningMilking frequencyDairy goat

a b s t r a c t

Twenty-four dairy goats of 3 breeds (Majorera, Tinerfena, and Palmera) in mid lactation(110 ± 7 d in milk) were milked unilaterally at 2 frequencies (once: X1 or twice daily: X2)for 6 wk to evaluate milk yield and milk composition and to compare two milk distribu-tion structures. On the sampling days, milk volumes of each udder halves were recordedand analyzed. Milk partitioning was divided into: cisternal (CM) and alveolar milk (AM);and into: machine milk (MM), machine stripping milk (MSM), and residual milk (RM). InMajorera and Tinerfena breeds did not find significant differences in milk yield and milkcomposition due to milking frequency. In contrast, Palmera goats had an increase of 14%in milk yield when they were milked X2 compared with X1, but the protein content wassignificantly higher in the milk of X1 (3.92%) than X2 (3.72%). Furthermore, the absenceof differences in protein daily yield between X1 and X2, suggested that cheese yield couldnot be maintained. Milking frequency did not affect CM and AM percentages in the studiedbreeds. Regarding breed factor, Majorera and Palmera had the highest and lowest CM per-centages, respectively, both in X1 and X2. On the other hand, MM and MSM percentages didnot differ due to milking frequency in Tinerfena and Palmera breeds. However, Majoreragoats had significant differences in MM (77.29 vs. 71.66%) and MSM (12.67 vs. 17.41%) forX1 and X2, respectively. A breed effect was observed on MM and MSM fractions: Major-era goats had higher MM percentages, while Tinerfena and Palmera goats had higher MSMpercentages. RM fraction was not affected by milking frequency or breed factors. Finally, nosignificant correlation coefficients were detected when comparing CM and AM with MM,MSM and RM fractions, which indicates that both milk partitioning structures did not seemto be comparable between them, at least in goat udders that have a more horizontal teatinsertion.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The mammary glands in ruminants are composed offunctionally separate glands (four in cows and two ingoats and sheep). Each gland has its own secretory tis-sue and cisternal cavities, and each gland is drained by

∗ Corresponding author at: ICIA, Apto. de correos 60, La Laguna 38200,Tenerife, Spain. Tel.: +34 922542800; fax: +34 922542898.

E-mail addresses: [email protected], [email protected] (J. Capote).

a separate teat (Bruckmaier and Blum, 1998). Accordingto Wilde and Knight (1990), the unilateral alteration ofmilking frequency indicates that milk yield changes areimposed by local intramammary mechanisms and affectsonly the treated gland. In addition, Wall and McFadden(2008) explained that experimental design that appliedsingle gland milking eliminated variation among animalsdue to environment, nutrition and genetic factors andexposed each gland to the same systemic factors.

Milk is stored in two interconnected anatomical uddercompartments that determine the milkability (Salama

0921-4488/$ – see front matter © 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.smallrumres.2013.04.013


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et al., 2004). Cisternal milk (CM) is located in the cisternalcompartment consisting of the gland cistern, the teat cis-terns and the large ducts; while alveolar milk (AM) is storedwithin the alveoli and small interlobular ducts (Marnet andMcKusick, 2001). Milk partitioning between both compart-ments varies according to specie, breed, age, lactation stage,parity and milking interval (Salama et al., 2004; Castilloet al., 2008). Partitioning between CM and AM was for-merly determined by drainage of cisternal milk, by using ateat cannula (Peaker and Blatchford, 1988), but new tech-niques include the use of an oxytocin receptor antagonistto block spontaneous milk ejection (Wellnitz et al., 1999).

Differing from dairy cows, small ruminants have pro-portionally larger cisterns which play an important rolein the storage of milk between milkings and can greatlyaffect the removal of milk at the time of milking (Marnetand McKusick, 2001). Furthermore, udder morphology ofmany goat and sheep breeds is characterized by having amore horizontal teat insertion (Rovai et al., 2008; Torreset al., 2013), a circumstance that implies manual inter-vention for complete milk removal. Milk collected duringmilking can be divided into: machine milk (MM) obtainedbetween attaching the line and the final cessation of themilk flow without the operator having to manipulate theudder; and machine stripping milk (MSM) which requiresmanual intervention to remove milk not obtained by themachine. Moreover, a milk fraction known as residual milk(RM) remains in the mammary tissue and it can only be col-lected after administration of pharmacological amounts ofoxytocin (Bruckmaier and Blum, 1998).

The goals of this study were to evaluate the effects ofunilateral milking frequency on milk yield, milk composi-tion and milk component yield; and to compare two milkdistribution structures in 3 dairy goat breeds milked at 2frequencies, and whether there are relevant correlationsamong them to establish a relationship between CM andAM with MM, MSM and RM.

2. Materials and methods

The experimental animal procedures were approved by the EthicalCommittee of the Universidad de Las Palmas de Gran Canaria (Arucas,Spain). A total of 24 dairy goats in mid lactation (110 ± 7 DIM) of Majorera(n = 8; 2.7 ± 0.4 L/d; parity = 3.4 ± 1.1), Tinerfena (n = 8; 2.3 ± 0.5 L/d; par-ity = 3.1 ± 1.3), and Palmera (n = 8; 1.8 ± 0.4 L/d; parity = 3.1 ± 1.2) breedsfrom the experimental farm of the Instituto Canario de InvestigacionesAgrarias (ICIA, Tenerife, Spain) were used. The animals were fed with com-mercial concentrate, maize, lucerne, wheat straw and a vitamin–mineralcorrector in accordance with the guidelines issued for lactating goatsby Institut National de la Recherche Agronomique (INRA, Paris, France;Jarrige, 1990). The milking frequency before the start of the experimentalperiod was once per day. Goats were milked in a double 12-stall paral-lel milking parlor equipped with recording jars (4 L ±5%) and a low-linemilk pipeline. Milking was performed at a vacuum pressure of 42 kPa, apulsation rate of 90 pulses/min, and a pulsation ratio of 60/40. The milk-ing routine included wiping dirt off teat ends and stripping 2–3 squirtsof milk from each teat, machine milking, machine stripping before clus-ter removal, and teat dipping in an iodine solution (P3-cide plus; HenkelHygiene, Barcelona, Spain).

During a 6-wk period, goats were milked once daily in the left mam-mary gland (X1; at 07:00 h), whereas the right mammary gland wasmilked twice daily (X2; at 07:00 and 17:00 h). Before the start of the exper-imental period, the goats were exposed to 3 wk of adaptation to X2. Milkvolumes were measured by using the recording jars in the milking parlorfor each udder half. On the sampling days (wk 2, 4, and 6), milk yield wasrecorded as MM plus MSM once daily for X1, and MM and MSM twice

daily for X2, according to Capote et al. (2008). Fat (4.0%)-corrected milk(FCM) was calculated according to Salama et al. (2003). Milk samples wereanalyzed immediately after collection to determine milk composition. Fat,protein, lactose and total solids were determined using a MilkoScan 133analyzer (Foss Electric, Hillerod, Denmark). Milk composition of X2 wascalculated by a weighted average from the a.m. and the p.m. milk compo-sition. Milk component yields were calculated by multiplying milk yieldby corresponding milk component percentages.

Milk partitioning was calculated at the a.m. milking (24- and 14-hmilking intervals for X1 and X2, respectively). During wk 1, 3, and 5, onthe sampling days, each goat was injected intravenously with 0.8 mg ofan oxytocin receptor blocking agent (Tractocile; Ferring, Madrid, Spain)inside a holding pen immediately before entering the milking parlor torecord CM volume. After CM removal, the goats were injected intra-venously with 2 IU of oxytocin (Oxiton; Laboratorios Ovejero, León, Spain)to reestablish milk ejection, and AM was measured. During wk 2, 4, and 6,on the sampling days, milk partitioning was divided into MM, MSM per-formed by the same milker, and RM obtained after injecting goats with2 IU of oxytocin.

A MIXED model procedure (SAS 9.0; SAS Institute Inc., Cary, NC) wasused. The statistical model included the fixed effects of milking frequency(X1 or X2) and breed (Majorera, Tinerfena, or Palmera), the random effectof the half-udder nested within animal, the respective interactions, andthe residual error:

Yijk = � + Bi + Mj + Gk + (BM)ij + εijk

where Yijk is the observation of the dependent variable, � is the overallmean, Bi is the effect of the breed i (i = 3), Mj is the effect of the milking fre-quency j (j = 2), Gk is the random effect, (BM)ij is the effect of the interactionbetween breed and milking frequency, εijk is the residual error.

Differences among the breeds and milking frequencies were evaluatedusing a multiple comparison test following the Tukey–Kramer method.Pearson’s correlation coefficients between milk fractions were also calcu-lated. Statistical differences were considered significant at P < 0.05. Dataare presented as least squares means.

3. Results

Milk yield and FCM (Table 1) did not differ due to milk-ing frequency in Majorera and Tinerfena breeds (P > 0.05).Nevertheless, Palmera breed had a significant increase inmilk yield by 14% when they were milked X2 comparedwith X1. Furthermore, FCM of X2 was higher than in X1udder halves by 18% in Palmera goats (P < 0.05). Regardingbreed effect, Majorera goats had higher milk yield valuesthan Palmera goats both in X1 and X2 (P < 0.05).

No differences were found in fat percentages in the stud-ied breeds (Table 1) when the milking frequency effect wasconsidered (P > 0.05). Besides, Palmera breed had highermilk fat content than Majorera and Tinerfena both in X1 andX2, but the differences were significant only in X2. Milkingfrequency did not have effect on the protein percentages inMajorera and Tinerfena goats (Table 1). However, Palmeragoats had higher milk protein content in X1 than in X2udder halves (P < 0.05). Regarding breed effect, Majoreraand Tinerfena had lower protein fraction than Palmera bothin X1 and X2 (P < 0.05).

No significant differences were detected in lactose con-tent among breeds and milking frequencies (Table 1),ranging from 4.78 to 4.86% in the studied conditions. Like-wise, total solids percentages were not affected due tomilking frequency (Table 1) (P > 0.05). Moreover, differ-ences in total solids percentages were found when thebreed effect was considered (P < 0.05). Thus, Palmera goatshad higher values than Majorera and Tinerfena both in X1and X2.

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Table 1Milk yield, milk composition and milk component yield of each udder half of three dairy goat breeds milked once (X1) or twice (X2) daily.a

Parameter Goat breed SEM

Majorera Tinerfena Palmera

X1 X2 X1 X2 X1 X2

Milk yield (L/d) 1.39ab 1.51a 1.27ab 1.31ab 1.04c 1.19b 0.049FCMb (L/d) 1.34a 1.50a 1.21ab 1.28a 1.05b 1.24a 0.045Fat (%) 3.79b 3.94b 3.76b 3.88b 4.06ab 4.29a 0.060Protein (%) 3.67bc 3.59c 3.63bc 3.51c 3.92a 3.72b 0.041Lactose (%) 4.83 4.86 4.85 4.83 4.78 4.81 0.028

Total solids (%) 12.99b 13.06b 12.92b 12.91b 13.58a 13.53a 0.083

Fat (g/d) 52.47a 59.42a 46.90ab 50.00ab 41.77b 50.98a 1.785Protein (g/d) 50.95a 54.40a 44.78ab 44.73ab 40.79b 44.45ab 1.504Lactose (g/d) 67.20ab 73.65a 61.70ab 64.22ab 49.96c 57.48b 2.513

Total solids (g/d) 180.42a 197.58a 162.07ab 168.04a 141.01b 161.42a 5.936

a–cMeans with different superscripts within the same row are different (P < 0.05).a Data are least squares means and standard error of means.b FCM = total milk yield (L/d) × (0.400 + 0.150 × total fat content (%)).

Majorera and Tinerfena goats were not different in milkcomponent yields between X1 and X2 (Table 1). In contrast,Palmera goats had significant increases by 22%, 15%, and14% in X2 daily yields of fat, lactose and total solids, respec-tively, compared with X1. However, protein yield did notsignificantly increase as did the other milk components.

CM and AM percentages (Table 2) did not differ due tomilking frequency in the studied breeds (P > 0.05). Majoreraand Palmera had the highest and lowest CM percentages,respectively, both in X1 and X2 (P < 0.05). In the same way,MM and MSM percentages (Table 2) were not affectedby milking frequency in Tinerfena and Palmera breeds(P > 0.05). However, Majorera goats had higher and lowervalues in MM and MSM fractions, respectively, in X1 withregard to X2. RM percentages were not affected by the milk-ing frequency and breed factors (P > 0.05), ranging from10.66 to 14.49% in the studied conditions.

Correlation coefficients among milk fractions arereported in Table 3. High negative correlations betweenMM and MSM fractions (P < 0.05) were observed forX1 (Majorera, r = −0.76; Tinerfena, r = −0.94; Palmera,r = −0.90) and X2 (Majorera, r = −0.72; Tinerfena, r = −0.70;Palmera, r = −0.90). Moreover, MM and RM were only sig-nificantly correlated for X1 (Majorera, r = −0.82; Tinerfena,

r = −0.93; Palmera, r = −0.86). In addition, no significantcorrelation coefficients were found between MSM and RMfor X1 and X2. Finally, CM and AM were not correlated withMM, MSM and RM fractions in the studied breeds milkedat X1 and X2 (P > 0.05).

4. Discussion

The increase in milk yield in Palmera goats was higherthan the values reported in Tinerfena goats (6%) by Capoteet al. (1999) and Damascus goats (7%) by Papachristoforouet al. (1982) and similar to loss caused by X1 in Alpinegoats (16%) by Komara et al. (2009). The increase in FCMin Palmera goats was comparable with the FCM valuereported in Murciano-Granadina goats (18%) by Salamaet al. (2003). However, the goats of those studies weremilked with the same frequency in both glands. The unilat-eral milking frequency effect indicates that the increase inmilk yield is a response strictly at the level of the mam-mary gland via local factors, and not due to the greateravailability of nutrient supply caused by the suppressionof milking in the opposite gland (Nudda et al., 2002; Walland McFadden, 2008).

Table 2Milk fractions of three dairy goat breeds milked once (X1) or twice (X2) daily.a,b

Fractionc Goat breed SEM

Majorera Tinerfena Palmera

X1 X2 X1 X2 X1 X2

CM (%) 82.28a 81.75a 80.12ab 80.30ab 77.22bc 76.70c 0.528AM (%) 18.41c 18.77c 20.15bc 19.99bc 23.02ab 23.43a 0.498MM (%) 77.29a 71.66b 67.21bc 61.21c 65.86bc 59.07c 1.366MSM (%) 12.67c 17.41b 19.71b 24.94ab 22.34ab 27.57a 1.100RM (%) 10.66 11.61 12.96 14.49 12.48 13.24 0.449

a–cMeans with different superscripts within the same row are different (P < 0.05).a Data are least square means and standard error of means.b Milk fractions were measured at 24- and 14-h milking intervals for X1 and X2 goats, respectively.c CM, cisternal milk; AM, alveolar milk; MM, machine milk; MSM, machine stripping milk; RM, residual milk.


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Table 3Pearson’s correlation coefficients matrix among milk fractions of three dairy goat breeds milked once (above diagonal) or twice (below diagonal) daily.

Breed Fractiona

CM AM MM MSM RM

CMMajorera −0.885* −0.285 0.379 0.181Tinerfena −0.989* 0.084 −0.050 −0.159Palmera −0.987* −0.051 0.162 0.007

AMMajorera −0.892* −0.007 −0.245 0.173Tinerfena −0.935* −0.189 0.143 0.232Palmera −0.990* 0.008 −0.136 0.023

MMMajorera 0.411 −0.550 −0.761* −0.823*

Tinerfena 0.067 −0.082 −0.941* −0.933*

Palmera 0.617 −0.586 −0.897* −0.863*

MSMMajorera −0.164 0.314 −0.721* 0.139Tinerfena 0.158 −0.210 −0.702* 0.694Palmera −0.615 0.636 −0.895* 0.666

RMMajorera 0.128 0.053 −0.050 −0.258Tinerfena −0.476 0.433 −0.253 −0.107Palmera 0.024 −0.107 −0.406 0.006

* P < 0.05.a CM, cisternal milk; AM, alveolar milk; MM, machine milk; MSM, machine stripping milk; RM, residual milk.

The differences observed in milk yield in Majorera, Tin-erfena and Palmera goats between X1 and X2 may beexplained as a consequence of cisternal capacity of eachbreed (Bruckmaier and Blum, 1998). A large voluminouscistern takes more time in filling up, delaying the effectsof the intramammary feedback inhibitor, intramammarypressure, or tight junction integrity on milk transferencefrom the alveoli to the cisterns, during the filling of theudder (Capote et al., 2008). Recently, serotonin has beenproposed as a feedback inhibitor of lactation, being a com-ponent involved in milk regulation (Hernandez et al., 2008).However, milk yields did not differ between treatment andcontrol halves, which suggest that serotonin is not a localfactor.

In addition, Silanikove et al. (2000) showed in goatsand cows that the plasmin-induced �-casein f(1–28) pep-tide can serve as a local regulator on milk secretion byfunctioning as a potassium channel blocker, which wassubsequently confirmed in dairy cows by Silanikove et al.(2009). It is predicted that for milking intervals of less than20 h in goats and 18 h in cows, the concentration of casein-derived peptides, including the active component �-caseinf(1–28), would be higher in the cistern than in the alveoli;therefore, the alveoli will not be exposed to the full impactof the negative feedback signal of this peptide. Extendingmilk stasis beyond these times exceeds the storage capac-ity of the cistern, resulting in the equilibration of �-caseinf(1–28) concentration between the cistern and the alveoli(Silanikove et al., 2010).

Thus, animals with smaller udder size, and hence ofcisternal compartment, such as Palmera goats (Suárez-Trujillo et al., 2013; Torres et al., 2013), are more affectedby mechanisms of feedback inhibition. Silanikove et al.(2010) explained that high milk producing goats, as Saa-nen, selected to high alveolar to cistern compartment ratio,are the most sensitive to changes in milking frequency. Incontrast, medium milk producing goats, as some Spanishbreeds, may attain their genetic potential for milk yield in

X1 regimen due to selection for high cistern capacity. Thephysiological explanation relates to the suggestion that �-casein f(1–28) is effective only in the alveoli where it isin contact with the epithelial cells. Exposing the alveoli tohigh concentration of �-casein f(1–28) will induce disrup-tion of the tight junction (Silanikove et al., 2010).

Milk fat content was not affected by milking frequencywhich is in accordance with Komara et al. (2009), who alsodid not observe differences in fat globule size between X1and X2 for Alpine goats. However, Salama et al. (2003)showed that milk of X1 goats had a 10% more fat con-tent than milk of X2 goats. Milk fat is considered to bethe most variable component in ruminant milk, due todiffering regulatory mechanisms for secretion of milk fatglobules relative to the components in the aqueous phaseof milk and to the transfer between alveolar and cister-nal compartments (Salama et al., 2003). X1 managementin high-yielding goats is a potent stressor that is able todisturb alveolar milk ejection because alveolar milk wasshown to contain up to 75% of milk fat when milk ejectionwas inhibited (Labussière, 1988). However, the absence ofsignificant differences in the studied breeds might be dueto the fact that approximately 80% of total milk was storedin the cisternal compartment and most of the transfer ofmilk fat from the alveoli to the cistern had already takenplace.

Milk protein concentration was significantly higher inX1 than in X2 udder halves in Palmera goats, which agreeswith observations in dairy goats by Komara et al. (2009)and dairy ewes by Nudda et al. (2002). Salama et al. (2003)explained that the concentration effect of the protein in X1with respect to X2 was due to the milk volume, this waslower with X1 but the casein synthesized remained andbecame more concentrated in the milk.

In goats, Capote et al. (1999) found that milking fre-quency did not affect lactose percentage and reiterate theassertion that lactose is the milk component least influ-enced by breed and milking factors, indicating a similar

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performance of the synthetic activity of the mammarygland.

In the studied breeds there were no significantdifferences found in total solids content between X1and X2. There is disagreement about the milking fre-quency effects on total solids percentages. Capote et al.(1999) had observed a lower total solids fraction inX1 (12.48%) than X2 (12.84%), while for Salama et al.(2003) the total solids were higher in X1 (13.60%) thanX2 (12.90%) in goats during an entire lactation. Finally,the fact that Palmera goats had higher percentages oftotal solids than Majorera and Tinerfena both in X1and X2, may be explained because the Palmera hadhigher percentages of fat and protein than the other twobreeds.

The increases in fat, lactose, and total solids yields wereconsistent with the significant increase in the milk produc-tion of Palmera goats. However, the absence of differencesin protein yield between X1 and X2 can be explained bya lower concentration of protein in X2, suggesting thatcheese yield could not be maintained. Marnet and Komara(2008) explained that the regulation of milk componentssynthesis is dependent on the duration of the milkinginterval, which can influence cheese-making capacity andcheese quality.

Despite the differences in milk yield in Palmera goatsbetween X1 and X2, there were not differences in the dis-tribution of milk in the udder. Salama et al. (2004) did notfind differences in milk accumulation rates in the cisternalcompartment at 16 and 24 h in Murciano-Granadina goatsmilked X1 or X2, whereas Torres et al. (2013) suggested thatthe high percentages of milk stored in cisternal compart-ments for 14- and 24-h milking intervals may be explainedby a greater transfer of milk from the alveoli to the cisternsduring early udder filling. The differences in milk partition-ing among breeds were due to the cisternal size of eachbreed that influences the capacity to store milk in this com-partment. For example, Rovai et al. (2008) found CM–AMratio of 59–41 and 77–23 for Manchega and Lacauneewes, respectively, where Lacaune breed presented agreater cisternal area than Manchega breed (24.0 vs.12.4 cm2).

MM and MSM percentages were higher and lower,respectively, in X1 udder halves in the studied breeds, butthe differences were significant only in Majorera goats.Previously, Capote et al. (2009) found no differences inMM percentages between X1 (67.8%) and X2 (64.5%) inTinerfena goats of high milk production, while MSM per-centages were higher in X2 (27.8%) than X1 (20.7%), andRM percentages were higher in X1 (11.5%) than X2 (7.7%),suggesting that an increase in milking frequency in a nor-mal routine implies greater stimulation and thus a highermilk drop to the cisterns. Moreover, Majorera goats hada higher and lower MM and MSM percentages, respec-tively, than Tinerfena and Palmera goats. Caja et al. (1999)explained that quantities of milk in each partition obtainedby mechanical milking depend on the udder morphologyand the development of cisternal and canalicular systems;which suggests a high variability between breeds and evenbetween animals of same breed. RM percentages were notaffected by the breed, and they were similar than those

reported in Murciano-Granadina (9–11%; Peris et al., 1996)and Tinerfena (7–12%; Capote et al., 2009) goats.

In addition, Marnet and McKusick (2001) reported sig-nificant increases in MSM percentage without proportionalmodification of AM or CM volume in Lacaune ewes betweenthe years 1982 and 1992. The increase in MSM fraction wasa consequence of the tendency to have more horizontallyplaced teats in the udder which increases cisternal stor-age capacity to improve milk production (Bruckmaier et al.,1997; Marnet and McKusick, 2001).

High negative correlations observed between MM andMSM fractions both in X1 and X2 in the studied breeds dif-fers with these observed by Peris et al. (1996) and Caja et al.(1999) who did not find significant correlations betweenboth fractions. However, it is clear that the correlationbetween both them could help in the selection of goats toimprove the milkability. Furthermore, Peris et al. (1996)noted that the negative correlation between MM and RMin goats could reduce the milking time because they accu-mulate more milk into the cisterns.

Although, CM and AM (Salama et al., 2004) or MM, MSMand RM percentages (Capote et al., 2008) have a strongdependence on udder morphology, the absence of signif-icant correlation coefficients between CM and AM withMM, MSM, and RM fractions impeded the establishment ofa relationship between both milk partitioning structures,at least in goat udders that have a more horizontal teatinsertion.

5. Conclusion

The results demonstrated that X2 practice did notimprove the milk production of the Majorera and Tin-erfena breeds, so it is a consequence of the adaptationof these breeds to X1, which is an interesting issue ingoat production systems, because it requires fewer variablecosts. Nevertheless, the high increase in milk yield in thePalmera goats due to X2 could seem a profitable manage-ment at certain times during the lactation. However, thispractice did not produce an increased in milk protein yieldin accordance with milk yield. Therefore, other studies arerequired to evaluate how the milking frequency affects thecheese yield, which is a very important part of the CanaryIslands livestock economy. Additionally, the knowledge ofthe structures of milk partitioning can serve as a basis forfuture selection programs to improve the milkability of thestudied breeds. Furthermore, if a wider selection of breedscould be studied, ranging from low milk yielding to highmilk yielding breeds, the relationship among milk fractionswould be more noticeable.

Conflict of interest

None.

Acknowledgment

This work was supported by Fondo Europeo deDesarrollo Regional-Instituto Nacional de Investigación yTecnología Agraria y Alimentaria (FEDER-INIA) RTA2009-00125.


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MANUSCRITO 3

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Short-term effects of milking frequency on milk yield, milk composition, SCC and 1

milk protein profile in dairy goats 2

Alexandr Torres1, Lorenzo-Enrique Hernández-Castellano2, Antonio 3

Morales-delaNuez2, Davinia Sánchez-Macías3, Isabel Moreno-Indias2, 4

Noemi Castro2, Juan Capote1 and Anastasio Argüello2* 5

1 Instituto Canario de Investigaciones Agrarias, La Laguna, Tenerife 38200, Spain. 6

2 Department of Animal Science, Universidad de Las Palmas de Gran Canaria, Arucas 7

35413, Spain. 8

3 Agroindustrial Engineering Department, Universidad Nacional de Chimborazo. 9

Riobamba 060150, Ecuador. 10

* Corresponding author: Anastasio Argüello, Fac. Veterinaria s/n, 35413 Arucas, Spain. 11

Tel.: +34 928451094; fax: +34 928451142. E-mail address: [email protected] 12

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The goats in Canary Islands are milked once daily by tradition, but in other areas, is 25

carried out two times, with an increase of milk yield. Therefore it is important know if 26

the increase of milking frequency can improve the production without impairing the 27

milk quality. The objective of this study was to investigate the short term effects of 3 28

milking frequencies on milk yield, milk composition, SCC, and milk protein profile in 29

dairy goats traditionally milked once a day. Twelve Majorera goats in early lactation (48 30

± 4 d in milk) were used to determine the milk yield, milk composition, somatic cell 31

count, and milk protein profile at 3 different milking frequencies. During a 5-wk period, 32

goats were milked once a day (X1) at wk 1 and 5, twice a day (X2) at wk 2 and 4, and 33

three times a day (X3) at wk 3. Milk recording and sampling were done on the last day 34

of each experimental week. Milk yield increased by 26% from X1 to X2. No differences 35

were obtained when switched from X2 to X3, and from X3 to X2. The goats recovered 36

the production level when they returned to X1. Different patterns of changes in the milk 37

constituents due to milking frequency were observed. Fat percentages increased when 38

switched from X1 to X2, there was a significant decrease from X2 to X3, and continued 39

to decline as milking frequency was decreased. Protein and lactose percentages were 40

similar among X1, X2, and X3. SCC values were similar when goats were milked X1, 41

X2, and X3, but then increased slightly when milking frequency returned to X2 and X1. 42

Finally, different patterns were observed for caseins (αS1-CN, αS2-CN, β-CN, κ-CN). 43

Thus, milking frequency did not affect the proportion of αS1-CN in milk, while αS2-CN 44

and β-CN increased from X1 to X2, stayed stable from X2 to X3, and then decreased as 45

milking frequency decreased. In contrast, κ-CN decreased from X1 to X2, and 46

recovered to initial values when milking frequency was returned to X1. 47

48

Keywords: milking frequency, milk yield, milk quality, dairy goat. 49

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Goat research needs progress rapidly to reach the level of knowledge of other 50

species like cattle or sheep, especially in milk production (Argüello, 2011). Many 51

studies seek to implement management systems in dairy farms with extended milking 52

intervals, or to minimize additional cost associated with extra milking if it is 53

outweighed by the value of additional milk obtained as observed in dairy cows (Wall & 54

McFadden, 2008). Milking is done twice daily (X2) in countries with high-yielding 55

dairy goats (Capote et al. 2009). However, dairy farmers want to reduce their labor 56

requirements associated with milking, to devote time to other farm practices or to social 57

activities (Komara et al. 2009). In this way, the practice of once daily milking (X1) is 58

viewed with interest by dairy farmers. In contrast, thrice daily milking (X3) is a 59

relatively novel management practice and it is not generally used in small ruminants, 60

but in dairy cows it has emerged as an effective management tool for dairy farmers to 61

increase milk production (Wall & McFadden, 2008). 62

Silanikove et al. (2010) explained that high milk producing goats, as Saanen, 63

selected to high alveolar to cistern compartment ratio, are the most sensitive to changes 64

in milking frequency. In contrast, medium milk producing goats, as Majorera, may 65

attain their genetic potential for milk yield in X1 regimen due to selection for high 66

cistern capacity (Torres et al. 2013). Previous studies revealed losses in milk yield of 67

X1 of 8 to 45% compared to X2 (Mocquot & Auran, 1974; Capote et al. 2009) and 68

increases of 8 to 28% when the goats were milked X3 instead of X2 (Henderson et al. 69

1985; Boutinaud et al. 2003). The wide variation in milk yield due to milking frequency 70

in the literature reports is a consequence of differences in breed, lactation stage, level of 71

production, duration of X1, X2 or X3, and individual characteristics (Marnet & 72

Komara, 2008). Additionally, the regulation of milk components synthesis and somatic 73


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cells are dependent on the milking intervals, which can influence on the milk quality 74

(Marnet & Komara, 2008). 75

The hypothesis of this research paper is that 3 milking frequencies might have 76

minor effect on milk yield and chemical composition in a goat breed that is generally 77

milked X1. In addition, no information regarding the influence of milking interval on 78

milk protein profile in dairy goats is available. Therefore, the objective of this study was 79

to investigate the short term effects of 3 milking frequencies on milk yield, milk 80

composition, SCC, and milk protein profile in dairy goats traditionally milked X1. 81

82

Materials and Methods 83

The experimental animal procedures were approved by the Ethical Committee of 84

the Universidad de Las Palmas de Gran Canaria. A total of 12 Majorera goats were in 85

second parity with 48 ± 4 DIM at the beginning of the experiment. The goats which 86

were used in the experiment were from the experimental farm of the Faculty of 87

Veterinary of this University. Kids were separated from their dams within 8 h of birth. 88

The milking frequency before the start of the experimental period was once per day. 89

During a 5-wk period, goats were milked: once daily at wk 1 and 5 (X1, at 09:00), twice 90

daily at wk 2 and 4 (X2, at 09:00 and 17:00), and thrice daily at wk 3 (X3, at 09:00, 91

13:00, and 19:00). The animals had access to wheat straw ad libitum and a vitamin-92

mineral corrector. The supplement per goat was 800 g/d of alfalfa and 1200 g/d of a mix 93

of maize, lucerne, and dehydrated beetroot, which it meets the nutritional requirements 94

in accordance with the guidelines issued for lactating goats by Institut National de la 95

Recherche Agronomique (INRA, Paris, France; Jarrige, 1990). The amount of 96

supplement did not differ according to milking frequency. Goats were milked in a 97

double 12-stall parallel milking parlor (Alfa Laval Iberia SA, Madrid, Spain) equipped 98

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with recording jars (4 L ± 5%) and a low-line milk pipeline. Milking was performed at a 99

vacuum pressure of 42 kPa, a pulsation rate of 90 pulses/min, and a pulsation ratio of 100

60/40, in accordance with Capote et al. (2009). The milking routine included machine 101

milking and stripping milking, done by the operator to remove the remaining milk from 102

the udder before cluster removal; and teat dipping in an iodine solution (P3-cide plus; 103

Henkel Hygiene, Barcelona, Spain). 104

Milk recording and sampling were done on the last day of each experimental 105

week. Milk yield (L/d) was calculated by adding milk volume at every milking by using 106

the recording jars in the milking parlor. Milk samples (50 ml) were analyzed 107

immediately after collection at the a.m. milking to determine milk composition, SCC, 108

and milk protein profile. Fat, protein, lactose, and total solids percentages were 109

determined using a DMA2001 Milk Analyzer (Miris Inc., Uppsala, Sweden), and SCC 110

using a DeLaval somatic cell counter (DeLaval International AB, Tumba, Sweeden). 111

Milk proteins were separated by SDS-PAGE (12.5%) using a Bio-Rad slab 112

electrophoresis unit (Bio-Rad Laboratories, Hercules, CA, USA), based on the method 113

of Laemmli (1970). Protein concentration of the milk was determined with the Quick 114

Start™ Bradford Protein Assay (Bio-Rad Laboratories, Hercules, CA, USA), using 115

BSA as standard reference. Gels were loaded with a fixed protein level (40 µg) per line, 116

and were run at 200 V for 6 h. After electrophoresis, gels were stained for 90 min using 117

10% acetic acid, 40% methanol, and 0.05% (w/v) Coomassie Blue R-250 solution, and 118

then were destained for 15 h using 10% acetic acid and 40% methanol solution. The gel 119

images (Figure 1) were scanned (Gel Doc EQ, Bio-Rad Laboratories), and the relative 120

quantities of each band were determined by using the Quantity One software program 121

(Bio-Rad Laboratories). Each sample was analyzed on duplicate gels. Individual protein 122


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species were identified by comparing their relative mobilities with those of standard 123

proteins (Precision Plus ProteinTM Unstained Standards, Bio-Rad Laboratories). 124

The statistical analyses were performed by using SPSS 15.0 software (SPSS 125

Inc., Chicago, IL). Repeated measures analysis of variance (ANOVA), with adjustments 126

for non-sphericity (Greenhouse-Geisser correction), was applied to evaluate time-127

dependent milking frequency effects on milk yield and milk quality; followed by LSD 128

post-hoc tests. Statistical differences were considered significant at P < 0.05. Data are 129

presented as least squares means. 130

131

Results and Discussion 132

Milk yield increased by 26 ± 10% (P < 0.05) with increasing milking frequency 133

from X1 to X2 (Table 1). This increase in Majorera goats, which are traditionally 134

milked X1, was similar to loss caused by X1 (compared with X2) in Saanen goats 135

(26%) in late lactation reported by Boutinaud et al. (2003) during a short treatment 136

period (23 d). Subsequently, no significant differences in milk yield were obtained 137

between X2 and X3. This result does not agree with those of Boutinaud et al. (2003) 138

who found significant increases (8%) in milk yield for goats milked X3 compared with 139

X2. Finally, when the milking frequency was returned to X1, there was a recovery in 140

milk yield to initial values (P > 0.05). Previously, Capote et al. (2009) showed that 141

Tinerfeña goat breed, also generally milked X1, did not present significant increases 142

from X1 to X2 (9%) in high production level (> 2.4 L/d); but medium (between 1.9 and 143

2.4 L/d) and low (< 1.9 L/d) production level presented significant increases (25 and 144

20%, respectively) for 24 wks of lactation, suggesting that lower difference between X1 145

and X2 in high production goats is a consequence of a wider cisternal capacity which 146

allows a continuous drop of alveolar milk to the cistern, reducing the feedback inhibitor 147

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process and the intramammary pressure. Otherwise, the absence of increase from X2 to 148

X3 indicated that secretory activity of mammary cells was not modified at these 149

frequencies in goats usually milked X1. 150

Fat percentage had a significant increase when switched from X1 to X2, there 151

was a significant decrease from X2 to X3, and continued to decline as milking 152

frequency was decreased (Table 1). The higher fat content of X2 milk compared to X1 153

may be due to the length of the preceding milking interval, in X2 was 16 h and in X1 154

was 24 h. However, McKusick et al. (2002) in dairy ewes and Torres et al. (2013) in 155

dairy goats explained that transfer of milk fat from the alveoli to the cistern occurs 156

during early udder filling, and this transfer no longer takes place during later intervals. 157

In addition, some researchers have observed no effect of milking frequency on fat 158

percentage (Komara et al. 2009), whereas other studies have found a negative 159

correlation between milk yield and fat percentages due to milking frequency (Salama et 160

al. 2003). Capote et al. (1999) found that goats milked X2 showed a significant increase 161

in fat percentage compared to those animals milked X1, due to a higher proportion of 162

alveolar milk removed by X2 which is richer in fat. However, a decline in milk fat 163

fraction was observed when milking frequency was changed to X3 and then returned to 164

X2. Some research works on dairy ruminants studied the association of plasma cortisol 165

levels with different factors that cause stress as related to milking (Hopster et al. 2002; 166

Negrao et al. 2004). Previously, Raskin et al. (1973) found that cortisol may produce a 167

decrease in milk lipid formation from glucose and acetate. Therefore, more experiments 168

will be necessary to study the relationship between frequent milking and cortisol levels 169

in goats usually milked X1. 170

Milking frequency did not affect the protein percentages during the experimental 171

period (P > 0.05; Table 1). In accordance, Torres et al. (2013) reported no differences in 172


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milk protein percentages due to milking frequency in cisternal and alveolar fractions of 173

3 dairy breeds traditionally milked X1. However, Boutinaud et al. (2003) showed a 174

higher protein content in Saanen goats milked X1 compared with X2 and X3, which 175

suggested a specific leakage of serum protein into milk after modification of the 176

permeability of the mammary epithelium at longer milking intervals. Nevertheless, the 177

ability to support the extended intervals between milking of some dairy goat breeds 178

could be related to the capacity of the tight junctions to remain tight for a long period, 179

without modification of secretion of milk components regulated by it (Marnet & 180

Komara, 2008). 181

Similarly to protein percentages, lactose concentration was unaffected by the 182

studied milking intervals (P > 0.05; Table 1). This is in agreement with the results by 183

Henderson et al. (1985) between X2 and X3 in Saanen goats and with Torres et al. 184

(2013) between X1 and X2 in Majorera goats. In this way, Capote et al. (1999) 185

reiterated the assertion that lactose is the lactic component least influenced by breeding 186

and milking factors, indicating a similar performance of the synthetic activity of the 187

mammary gland. 188

Total solids stayed stable from X1 to X2 (P > 0.05; Table 1), and decreased from 189

X2 to X3 (P < 0.05). No corresponding results for X3 are available in dairy goats for 190

comparison, but Capote et al. (1999) and Salama et al. (2003) reported significant 191

differences in total solids percentages (12.48 vs.12.84% and 13.60 vs.12.90% for X1 192

and X2, respectively) in dairy goats during an entire lactation. The milk total solids are 193

a mixture of fat, protein, lactose and mineral matter. Thus, any variation on these 194

constituents can affect its concentration. In this case, milk fat was the most variable 195

component among milking frequencies, which involved changes in total solids 196

percentages. 197

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SCC values were unaffected by milking frequency when goats were milked X1, 198

X2, and X3; but then increased slightly when milking frequency returned to X2 and X1 199

(Table 1). There is disagreement about the milking frequency effects on SCC levels. 200

Some researchers have observed no effect of frequent milking on SCC in cows (Klei et 201

al. 1997), and ewes (de Bie et al. 2000), both in early lactation. Boutinaud et al. (2003) 202

showed that SCC tended to increase in X1, whereas it remained stable in X3 compared 203

with X2 in dairy goats. Likewise, Lakic et al. (2011) explained that prolonged milking 204

intervals as well as short milking intervals have influence on the milk SCC in cows. 205

Kamote et al. (1994) suggested that the increase in SCC in extended milking intervals in 206

dairy cows could be explained by a concentration effect. Paape et al. (2001) described 207

those stressful events as changes in the milking routine, to which goats are very 208

sensitive, may cause an increase in SCC even in the absence of an intramammary 209

infection. Therefore, the high values of SCC obtained during the final period seem to be 210

related with a physiological stress to the mammary gland caused by the experiment. 211

Changes in milk protein profile were found due to milking frequency (Table 2). 212

Thus, different patterns were observed for caseins (αS1-CN, αS2-CN, β-CN, κ-CN). 213

Milking frequency did not affect the proportion of αS1-CN in milk, while αS2-CN and β-214

CN increased from X1 to X2 (P < 0.05), stayed stable from X2 to X3, and then 215

decreased as milking frequency decreased. In contrast, κ-CN decreased from X1 to X2 216

(P < 0.05), and recovered to initial values when milking frequency was progressively to 217

X3 toward X1 (P > 0.05). Goats showed a significantly lower β-Lactoglobulin (β-Lg) 218

content in the final week of experimentation, whereas α-Lactalbumin (α-La) presented a 219

lower percentage when animals were milked X3. Lastly, there was not an effect of 220

milking frequency on lactoferrin (LF) and serum albumin (SA) concentration when 221

increasing from X1 to X3 (P > 0.05), and then had an enhanced trend when the milking 222


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frequency returned to X1. Immunoglobulin G heavy- (IgH) and light-chain (IgL) had a 223

decrease in concentrations from X1 to X2, but these differences were significant only 224

for IgL, then were maintained from X2 to X3, and tended to increase at the end of the 225

experiment. 226

The results for caseins are consistent with observations in dairy cows by 227

Sorensen et al. (2001), who found higher proportions of α-CN and β-CN and lower κ-228

CN when switched from X2 to X3 in either the long or the short term. However, these 229

authors indicated that β-Lg and α-La were not affected by milking frequency in the 230

short term. Regarding to SA, it has the same amino acid sequence as the blood serum 231

molecule, and it is commonly believed that SA enters the milk by leaking through the 232

epithelial tight junction from the systemic fluids, as was suggested by Boutinaud et al. 233

(2003). However, Shamay et al. (2005) showed that SA is produced and secreted by 234

epithelial cells into milk, indicating that it is part of the mammary gland innate immune 235

system. In addition, Hernández-Castellano et al. (2011) found that high milking 236

frequency affected the immunological milk parameters in Majorera goats, chiefly a 237

decreased on IgG concentration (immunosupression) presumably due to an increased in 238

the cortisol excretion by adrenal glands, caused by animal stress. 239

The changes in milk protein profile in cows have been associated with differing 240

proteolytic enzyme activities, such as plasmin, because the increase of milking 241

frequency reduces the time that milk is stored in the udder, and the time to degrade the 242

milk proteins is shorter (Sorensen et al. 2001). Previously, Bastian (1996) indicated that 243

plasmin causes degradation of β-CN to γ-CN, which influence the milk quality for 244

cheese production, and Grieve & Kitchen (1985) explained that κ-CN is more resistant 245

to proteolysis for bovine plasmin than α-CN and β-CN, which can explain that κ-CN 246

varied at the opposite to β-CN and αS2-CN when milking frequency was increased from 247

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X1 to X2. However, Svennersten-Sjaunja et al. (2007) reported a lower plasmin activity 248

when milking frequency was increased in dairy cows, but proteolytic degradation of 249

milk proteins was maintained. Therefore, more experiments will be necessary to 250

evaluate the plasmin activity at different milking frequencies and its effects on 251

degradation of milk proteins in dairy goats. 252

In conclusion, short-term changes of the normal milking frequency in goats 253

traditionally milked X1 during early lactation can affect milk production as reflected the 254

high increase in milk yield when milking frequency was increased from X1 to X2. 255

However, the changes in milk quality, especially in the fat content and milk protein 256

profile, requires new studies on how the milking frequency affect the yield and quality 257

of the cheeses, because the goat milk in Canary Islands is used mainly for cheese 258

production. In addition, the modification in milk yield did not take place when goats 259

were switched from X2 to X3, but the decreased in fat content requires further studies to 260

evaluate the factors that cause this decline. 261

262

This research was supported by grant AGL 2006-08444/GAN from the Spanish 263

Government. The authors want to thank A. Alavoine, G. Pons, V. Bissières, and S. 264

Cyrille from École Vetérinaire de Toulouse (France) for their technical assistance 265

during the experiment. 266

267

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Table 1. Milk yield, milk composition, and SCC from dairy goats milked at different 370

milking frequencies†‡ 371

Milking Frequency§

X1 X2 X3 X2 X1 SEM P value

Milk yield (L/d) 1.69b 2.13a 2.09a 2.01a 1.89b 0.127 0.001

Fat (%) 3.86b 4.38a 3.61b 3.34c 3.13c 0.084 0.001

Protein (%) 3.39 3.06 3.07 3.03 3.12 0.054 0.073

Lactose (%) 5.17 5.09 5.26 5.21 5.22 0.035 0.514

Total Solids (%) 13.24a 13.34a 12.74b 12.26c 12.30c 0.109 0.001

SCC (log/ml) 5.99ab 5.82b 5.88ab 6.21a 6.06a 0.077 0.050

a–cMeans with different superscripts within the same row are different (P < 0.05) 372

† Data are least squares means and standard error of means 373

‡ Milk composition and SCC were determined with milk samples from a.m. milking for 374

X2 and X3 375

§ X1 = once daily; X2 = twice daily; X3 = thrice daily 376

377

378

379

380

381

382

383

384

385

386

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Table 2. Protein profile from dairy goats milked at different milking frequencies†‡ 387

Milking Frequency§

Protein (%)¶ X1 X2 X3 X2 X1 SEM P value

αS1-CN 11.15 10.41 11.67 10.03 10.36 0.399 0.302

αS2-CN 16.22bc 20.86a 20.63a 18.05b 15.70c 0.975 0.001

β-CN 21.63b 25.95a 25.29a 24.39ab 22.85b 0.692 0.021

κ-CN 12.01a 9.24b 9.64b 8.29b 9.84ab 0.513 0.038

β-Lg 14.67a 15.44a 14.68a 15.39a 12.96b 0.449 0.045

α-La 10.43a 10.30ab 8.73b 9.95ab 11.52a 0.509 0.050

LF 3.02b 1.57b 2.10b 3.66ab 4.97a 0.558 0.007

SA 3.91ab 2.40b 3.22b 4.89a 5.30a 0.501 0.001

IgH 3.74ab 2.38b 2.61ab 3.28ab 4.20a 0.390 0.042

IgL 3.17a 1.45b 1.43b 2.09ab 2.31ab 0.421 0.010

a–cMeans with different superscripts within the same row are different (P < 0.05) 388

†Data are least squares means and standard error of means 389

‡Protein profile was determined with milk samples from a.m. milking for X2 and X3 390

§ X1 = once daily; X2 = twice daily; X3 = thrice daily 391

¶ CN = casein; β-Lg = β-lactoglobulin; α-La = α-lactalbumin; LF = lactoferrin; SA = 392

serum albumin; IgH = immunoglobulin G heavy-chain; IgL = immunoglobulin G light-393

chain 394

395

396

397

398

399


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Figure 1. SDS-PAGE patterns of milk proteins from dairy goats (lanes 1–9 and 11–13) 400

milked at different milking frequencies (X1 = once daily; X2 = twice daily; X3 = thrice 401

daily). 402

403

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Effects of oxytocin treatments on milk production in dairy goats 1

A. Torres,* J. Capote,* A. Argüello,† D. Sánchez-Macías,‡ A. Morales-delaNuez,† 2

and N. Castro,†1 3

*Instituto Canario de Investigaciones Agrarias, La Laguna, Tenerife 38200, Spain. 4

†Department of Animal Science, Universidad de Las Palmas de Gran Canaria, Arucas 5

35413, Spain. 6

‡Universidad Nacional de Chimborazo, Riobamba 060150, Ecuador. 7

1Corresponding author: Noemi Castro, Fac. Veterinaria s/n, Arucas 35413, Spain. 8

Tel.: +34 928451093; fax: +34 928451142. E-mail address: [email protected] 9

10

ABSTRACT 11

Two experiments were conducted to determine the effects of oxytocin treatments on 12

milk ejection. In experiment 1, 39 dairy goats in mid lactation (95 ± 10 days in milk) 13

were divided into 3 groups (n = 13) with similar milk yields. During an 8-wk period, 14

goats from group 1 (OT1) were introduced to the milking parlor once a week, 10 h after 15

morning milking, and all pre-milking routines were carried out, including stripping 2 to 16

3 squirts of milk from each teat, but the animals were not milked. During this period, 17

goats from group 2 (OT2) were injected intravenously with 2 IU of oxytocin in the 18

crowd pen once a week, 10 h after morning milking, but the animals were not milked. 19

Goats from group 3 (control) remained in the pen without any treatment. In experiment 20

2, 10 dairy goats in mid lactation (104 ± 5 days in milk) were divided into 5 groups (n = 21

2) with similar milk yields. During a 6-wk period, goats were milked once daily, except 22

for one day a week, when they were milked 3 additional times (at 1200, 1600, and 2000 23

h). On this day, after each milking, goats were administered intravenously with a dose 24

corresponding to oxytocin (0.5, 1, 2, and 4 IU), or saline solution (control). Machine 25


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milk and residual milk were recorded for each group. Additionally, milk yield, chemical 26

composition, and SCC of each group were determined for the 3 following days after 27

applying the treatments. In experiment 1, milk yield and milk composition were not 28

affected by OT1 and OT2, indicating that the oxytocin release by the stimulatory effect 29

of milking procedures or the administration of synthetically manufactured oxytocin, 30

have no galactopoietic effect on goats not milked immediately. In experiment 2, milk 31

partitioning and milk composition did not differ due to oxytocin treatments at 1200, 32

1600 and 2000 h, indicating that the contraction of the myoepithelial cells that surround 33

the mammary alveoli is similar between low and high doses of oxytocin. In addition, the 34

evolution of milk yield and SCC after the experimental day was not affected by the 35

treatments with oxytocin. 36

37

Keywords: oxytocin, dairy goat, milk yield, milk partitioning. 38

39

INTRODUCTION 40

In ruminants, milk ejection is a neuroendocrine reflex arc and it occurs in 41

response to suckling, manual stimulation of the mammary gland, or machine milking 42

(Macuhova et al., 2004). These stimulations cause on the udder the release of oxytocin 43

from the neural lobe of the pituitary into blood circulation, which induces contraction of 44

myoepithelial cells that surround the alveoli where milk is stored, and transfer it into the 45

cisternal space (Lollivier et al., 2002; Bruckmaier, 2003). However, not all alveolar 46

milk can be ejected if milk is not removed from the udder (Bruckmaier and Blum, 47

1998). 48

Depending on the stimulation of the mammary gland, it causes different 49

oxytocin responses. Suckling is a more potent stimulus than milking, while hand 50

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milking induces a more pronounced release of oxytocin than machine milking (Akers 51

and Lefcourt, 1982; Gorewit et al., 1992). Furthermore, prestimulation before milking is 52

important because it increases oxytocin levels and promotes early induction of milk 53

ejection to avoid an interruption of milk flow during early milking (Bruckmaier, 2001). 54

However, milk ejection during machine milking is not complete, even with an adequate 55

prestimulation. Usually a residual milk fraction remains in the udder which can be 56

obtained by injection of oxytocin, and it varies widely between breeds and even 57

between animals of the same breed (Peaker and Blatchford, 1988; Such et al., 1999). 58

Milk ejection in goats, in response to oxytocin, is similar to cows and sheep, but 59

milk removal is different due to udder morphology and milk partitioning (Bruckmaier 60

and Blum, 1998). In goats, oxytocin release is highly variable within and between 61

animals, being readily induced by tactile prestimulation or by the milking machine 62

(Bruckmaier and Blum, 1998; Marnet and McKusick, 2001). 63

In experiments of unilateral milking frequency of dairy goats, the effect of 64

oxytocin on milk yield and milk composition of the unmilked gland is still unknown. 65

For this reason, the first objective of the present study was to determine the effects of 66

endogenous and exogenous oxytocin on milk parameters in goats not milked 67

immediately. In addition, the second objective was to study the response to different 68

doses of exogenous oxytocin on milk ejection in dairy goats. 69

70

MATERIALS AND METHODS 71

Animal and Management Conditions 72

Two experiments were conducted on a total of 49 dairy goats in mid lactation. 73

The experiment 1 was performed on the experimental farm of the Instituto Canario de 74

Investigaciones Agrarias (Tenerife, Spain) on 39 dairy goats, while the experiment 2 75


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4

was carried out on the experimental farm of the Faculty of Veterinary of the 76

Universidad de Las Palmas de Gran Canaria (Arucas, Spain) on 10 dairy goats. The 77

experimental animal procedures were approved by the Ethical Committee of the 78

Universidad de Las Palmas de Gran Canaria. The animals were fed with maize, lucerne, 79

dehydrated beetroot, wheat straw, and a vitamin-mineral corrector in accordance with 80

the guidelines issued for lactating goats by Institut National de la Recherche 81

Agronomique (INRA, Paris, France; Jarrige, 1990). In both experiments, goats were 82

milked in a double 12-stall parallel milking parlor equipped with recording jars (4 L ± 83

5%) and a low-line milk pipeline. Milking was performed at a vacuum pressure of 42 84

kPa, a pulsation rate of 90 pulses/min, and a pulsation ratio of 60/40, in accordance with 85

Capote et al. (2006). The milking routine included wiping dirt off teat ends and 86

stripping 2 to 3 squirts of milk from each teat; machine milking and stripping milking, 87

done by the operator to remove the milk remaining in the udder before cluster removal; 88

and teat dipping in an iodine solution (P3-cide plus; Henkel Hygiene, Barcelona, Spain). 89

90

Experimental Procedures 91

Experiment 1. 39 Canarian dairy goats in second parity, with 95 ± 10 DIM, 92

were divided into 3 groups (n = 13) with similar milk yields. All goats were milked 93

once daily (at 0700 h) according to the normal milking routine. During an 8-wk period, 94

goats from group 1 (OT1) were introduced to the milking parlor once a week, 10 h after 95

morning milking, and all pre- and post-milking routines were carried out, including 96

stripping 2 to 3 squirts of milk from each teat and dipping of teats in an iodine solution 97

(P3-cide plus; Henkel Hygiene, Barcelona, Spain), but the animals were not milked. 98

Before the experimental period, OT1 goats were exposed to 3 wk of adaptation, where 99

the animals began to enter the milking parlor in the afternoon. During the experimental 100

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period, goats from group 2 (OT2) were injected intravenously with 2 IU of oxytocin 101

(Oxiton; Laboratorios Ovejero, León, Spain) in the crowd pen once a week, 10 h after 102

morning milking, but the animals were not milked at this time. Goats from group 3 103

(control) remained in the pen without any treatment. Milk recording and sampling were 104

done the next day at the morning milking. 105

Experiment 2. 10 Canarian dairy goats in second parity, with 104 ± 5 DIM, 106

were divided into 5 groups (n = 2) with similar milk yields. During a 6-wk period, goats 107

were milked once daily (at 0800 h), except one day a week, when they were milked 3 108

additional times (at 1200, 1600, and 2000 h). On this day, milk was collected after each 109

milking (machine milk), and after the complete cessation of milk flow, the groups were 110

injected intravenously with a dose corresponding to oxytocin (0.5, 1, 2, and 4 IU), or 111

saline solution (control) to remove the remainder of milk in the udder (residual milk). 112

Total milk was defined as machine milk plus residual milk. Additionally, milk yield, 113

milk composition (fat, protein and lactose), and SCC of each group were determined for 114

the 3 following days after applying the treatments. 115

In experiment 1, milk volumes were recorded by using the recording jars in the 116

milking parlor, while milk of each fraction of the experiment 2 was measured by a 117

graduated cylinder. Milk samples (experiment 1 and 2) were analyzed immediately after 118

collection to determine chemical composition. Fat, protein and lactose percentages were 119

determined by using a DMA2001 Milk Analyzer (Miris Inc., Uppsala, Sweden), and 120

SCC using a DeLaval somatic cell counter (DeLaval International AB, Tumba, 121

Sweeden). 122

123

Statistical Analysis 124

The statistical analyses were performed by using SPSS 15.0 software (SPSS 125

Inc., Chicago, IL). Repeated measures analysis of variance (ANOVA), with adjustments 126


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for non-sphericity (Greenhouse-Geisser correction), was applied to evaluate time-127

dependent effects of OT1 and OT2 on milk yield and milk composition (experiment 1), 128

and doses of oxytocin on milk partitioning and milk composition (experiment 2), 129

followed by LSD post-hoc tests. Differences among experimental groups (experiment 1 130

and 2) were evaluated using a multiple comparison test following the Tukey method. 131

Statistical differences were considered significant at P < 0.05. Data are presented as 132

estimated marginal means. 133

134

RESULTS AND DISCUSSION 135

Experiment 1. 136

In the 3 studied groups, it was observed, as expected, a decrease in milk yield at 137

the end of the experimental period (P < 0.05; Table 1). Capote et al. (2008) observed a 138

significant decrease in milk yield throughout lactation in dairy goats (2.51 vs. 2.08 L/d 139

in 12 and 20 weeks of lactation, respectively). The decline in milk production with 140

advancing lactation has been attributed to a gradual decrease in number of secretory 141

cells (Knight and Peaker, 1984). No differences were detected in milk yield (P > 0.05) 142

in any week of experimentation due to treatments. Therefore, the results indicate that 143

the oxytocin release by the stimulatory effect of milking procedures or the 144

administration of synthetically manufactured oxytocin, have no galactopoietic effect in 145

goats not milked immediately. Some studies have indicated that oxytocin release is not 146

an important factor for milk yield gain in small ruminants with large cisterns (Negrao et 147

al., 2001; Marnet and McKusick, 2001). However, it has been indicated that oxytocin 148

doses induce an increase in milk yield proportional to the capacity of cisternal storage 149

but only when accompanied by milk removal (Lollivier and Marnet, 2005a). 150

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Oxytocin treatments did not affect the milk composition (Table 1). Lollivier and 151

Marnet (2005b) observed changes in protein content due to oxytocin injection in dairy 152

goats not milked immediately (28.9 vs. 27.6 g/kg in control and oxytocin group, 153

respectively), but fat (33.2 vs. 34.3 g/kg) and lactose contents (44.9 vs. 45.3 g/kg) were 154

unaffected. In cows, Caja et al. (2004) demonstrated a back-flux of milk to the ductal 155

and alveolar compartments when they are not milked promptly after milk letdown, 156

which influences the transference of milk components, as the upward movement of the 157

fat globules in the opposite direction to the downward draining and newly secreted milk 158

(Ayadi et al., 2004). However, Salama et al. (2004) indicated the absence of recoil and 159

milk return from cistern to alveoli in goats, due to the greater cisternal milk percentages 160

and the small contact surface between the alveolar and cisternal compartments. 161

162

Experiment 2. 163

Total milk volumes and percentages of machine milk and residual milk at 1200, 164

1600 and 2000 h are presented in Table 2. No differences were observed in total milk 165

volumes due to treatments at different milking times (P > 0.05). Since the control goats 166

were not subjected to a complete emptying of the udder, the milk accumulated in the 167

alveoli and small ducts was transferred to the cistern and was obtained in the next 168

milking; while the other goats began to store milk in the alveolar tissue which was 169

ejected after having received doses of oxytocin. Thus, there was no effect of treatments 170

on total milk volume within the udder. On the other hand, percentages of residual milk 171

obtained after saline solution injection were lower (P < 0.05) in control group (< 20%) 172

than oxytocin groups (ranged from 38.31 to 59.79%) at 1200, 1600 and 2000 h, which 173

corroborate that oxytocin has an effect on the milk transfer from alveolar tissue to 174

cistern. Moreover, the absence of differences in the milk partitioning among the 4 175


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oxytocin groups at these intervals (P > 0.05), could indicate that the contraction of the 176

myoepithelial cells that surround the mammary alveoli is similar between low and high 177

doses of oxytocin. Previously, Lollivier et al. (2002) have indicated that a complete 178

milk removal is obtained following intravenous injection with 0.1 to 1 IU of oxytocin in 179

dairy goats. 180

Fat, protein and lactose percentages in machine and residual milk are shown in 181

Table 3. Fat percentages in machine milk significantly decreased between 1200 and 182

1600 h for the studied groups, and although another decline was observed between 1600 183

and 2000 h, the differences were not significant. A similar pattern was detected in fat 184

fractions of residual milk for the oxytocin groups between 1200 and 1600h. This decline 185

in milk fat content of both fractions could be due to cortisol released in response to the 186

stress caused by the experiment. Some research work on dairy ruminants studied the 187

association of plasma cortisol levels with different factors that cause stress in animals 188

(e.g., milking) (Hopster et al., 2002; Negrao et al., 2004). Previously, Raskin et al. 189

(1973) found that cortisol may produce a decrease in milk lipid formation from glucose 190

and acetate. In addition, no differences were observed in fat percent in milk fractions 191

among oxytocin groups at any studied milking time (P > 0.05). Gorewit and Sagi (1984) 192

observed that fat percentage in total residual milk was not affected by administration of 193

different doses of oxytocin (0.5, 1, 1.5, 2, and 3 IU) in dairy cows, but they used 194

different experimental techniques for determination of residual milk. 195

Protein and lactose percentages in machine milk and residual milk were not 196

affected due to oxytocin doses at 1200, 1600 and 2000 h (P > 0.05). In cows, some 197

authors claim that there is no modification of milk protein and lactose contents 198

regardless if oxytocin is administered over medium or long periods of time, indicating 199

that the effect of oxytocin is not manifested through an effect on cell activity (Nostrand 200

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et al., 1991; Ballou et al., 1993). However, Gorewit and Sagi (1984) observed that milk 201

protein percentage was lower for those cows receiving higher doses of oxytocin, 202

attributed to a dilution effect as a result of increased total milk yield. 203

Milk yield, chemical composition and SCC before (day 0) and after (day 1–3) 204

injecting different treatments are presented in Table 4. In all groups, an expected 205

decrease in milk yield at day 1 after applying the treatments was observed (P < 0.05). 206

This was because 12 hours had elapsed since the last milking. Therefore, the goats 207

stored less milk inside the udder. However, there was no effect due to treatments on 208

milk production in the following days (P > 0.05), recovering similar values to day 0. 209

Bruckmaier (2003) and Macuhova et al. (2004) found a reduction of milk ejection when 210

chronic oxytocin treatment (50 IU) was withdrawn in dairy cows. It seems that the 211

reduction of spontaneously removed milk was caused by reduced contractibility of 212

myoepithelial cells in the mammary gland at the normal physiological oxytocin 213

concentrations (Macuhova et al., 2004). 214

Fat percentages declined significantly at days 1 and 2 in all studied groups, but 215

at day 3 it reached similar values to day 0 (Table 4). In contrast, protein contents 216

increased at days 1 and 2, and subsequently decreased. Lactose percentages did not 217

show significant changes in the following days after experiment. This behavior could be 218

due to different regulatory mechanisms for secretion of milk components. No statistical 219

differences were found in SCC levels for the experimental days in the oxytocin groups 220

(Table 4). Allen (1990) observed that milk SCC increased in a dose dependent manner 221

at 12, 24, 36, 48, 60, and 72 h after the injected dose (1, 10, 100, or 1000 IU), and some 222

cows had a mastitis-like response with clots in the milk. Finally, variability of SCC 223

among the groups was high, and may be due to multiple individual factors (e.g., oestrus) 224

and not necessarily a response caused by treatments. 225


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226

CONCLUSIONS 227

The oxytocin release by the stimulatory effect of milking procedures or the 228

administration of synthetically manufactured oxytocin had no galactopoietic effect and 229

did not produce apparent changes in the milk composition on goats not milked 230

immediately, and that are traditionally milked once a day. Likewise, it did not produce 231

apparent changes in the milk composition. In addition, the absence of differences in the 232

milk partitioning and milk composition among the administration of 4 doses of oxytocin 233

indicated that the contraction of the myoepithelial cells that surround the mammary 234

alveoli is similar between low and high doses of oxytocin in dairy goats milked once a 235

day by tradition. 236

237

ACKNOWLEDGMENTS 238

This work was supported by Fondo Europeo de Desarrollo Regional-Instituto 239

Nacional de Investigación y Tecnología Agraria y Alimentaria (FEDER-INIA) 240

RTA2009-00125. 241

242

REFERENCES 243

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oxytocin and prolactin in parturient dairy cows. Horm. Behav. 15:87–93. 245

Allen, J. C. 1990. Milk synthesis and secretion rates in cows with milk composition 246

changed by oxytocin. J. Dairy Res. 73:975–984. 247

Ayadi, M., G. Caja, X. Such, M. Rovai, and E. Albanell. 2004. Effect of different 248

milking intervals on the composition of cisternal and alveolar milk in dairy 249

cows. J. Dairy Res. 71:304–310. 250

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Ballou, L. U., J. L. Bleck, G. T. Bleck, and R. D. Bremel. 1993. The effects of daily 251

oxytocin injections before and after milking on milk production, milk plasmin, 252

and milk composition. J. Dairy Sci. 76:1544–1549. 253

Bruckmaier, R. M., and J. W. Blum. 1998. Oxytocin release and milk removal in 254

ruminants. J. Dairy Sci. 81:939–949. 255

Bruckmaier, R. M. 2001. Milk ejection during machine milking in dairy cows. Livest. 256

Prod. Sci. 81:121–124. 257

Bruckmaier, R. M. 2003. Chronic oxytocin treatment causes reduced milk ejection in 258

dairy cows. J. Dairy Res. 70:123–126. 259

Caja, G., M. Ayadi, and C. H. Knight. 2004. Changes in cisternal compartment based on 260

stage of lactation and time since milk ejection in the udder of dairy cows. J. 261

Dairy Sci. 87:2409–2415. 262

Capote, J., A. Argüello, N. Castro, J. L. López, and G. Caja. 2006. Correlations between 263

udder morphology, milk yield and milking ability with different milking 264

frequencies in dairy goats. J. Dairy Sci. 89:2076–2079. 265

Capote, J., Castro, N., Caja, G., Fernández, G., Briggs, H., Argüello, A., 2008. Effects 266

of the frequency of milking and lactation stage on milk fractions and milk 267

composition in Tinerfeña dairy goats. Small Rumin. Res. 75, 252–255. 268

Gorewit, R. C., and R. Sagi. 1984. Effects of exogenous oxytocin on production and 269

milking variables of cows. J. Dairy Sci. 67:2050–2054. 270

Gorewit, R. C., K. Svennersten, W. R. Butler, and K. Uvnas-Moberg. 1992. Endocrine 271

responses in cows milked by hand and machine. J. Dairy Sci. 75:443–448. 272

Hopster, H., R. M. Bruckmaier, J. T. N. Van der Werf, S. M. Korte, J. Macuhova, G. 273

Korte-Bouws, and C. G. van Reenen. 2002. Stress responses during milking; 274


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comparing conventional and automatic milking in primiparous dairy cows. J. 275

Dairy Sci. 85:3206–3216. 276

Jarrige, J. 1990. Alimentación de bovinos, ovinos y caprinos. 1st ed. Mundi-Prensa, 277

Madrid, Spain. 278

Knight, C. H., and M. Peaker. 1984. Mammary development and regression during 279

lactation in goats in relation to milk secretion. Q. J. Exp. Physiol. 69:331–338. 280

Lollivier, V., J. Guinard-Flament, M. Ollivier-Bousquet, and P. G. Marnet. 2002. 281

Oxytocin and milk removal: two important sources of variation in milk 282

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42:173–186. 284

Lollivier, V., and P. G. Marnet. 2005a. Galactopoietic effect of milking in lactating 285

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Lollivier, V., and P. G. Marnet. 2005b. Comparative study of the galactopoietics effect 288

of oxytocin during and between milkings in cows and goats. ICAR Technical 289

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Macuhova, J., V. Tancin, and R. M. Bruckmaier. 2004. Effects of oxytocin 291

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Marnet, P. G., and B. C. McKusick. 2001. Regulation of milk ejection and milkability 294

in small ruminants. Livest. Prod. Sci. 70:125–133. 295

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oxytocin release and milk production in dairy ewes. Small Rumin. Res. 39:181–297

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Negrao, J. A., M. A. Porcionato, A. Passille, and J. Rushen. 2004. Cortisol in saliva and 299

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1718. 301

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exogenous oxytocin on lactation milk yield and composition, J. Dairy Sci. 303

74:2119–2127. 304

Peaker, M., and D. R. Blatchford. 1988. Distribution of milk in the in the goat 305

mammary gland and its relation to the rate and control of milk secretion. J. Dairy 306

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Raskin, R. L., M. Raskin, and R. L. Baldwin. 1973. Effects of chronic insulin and 308

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rats. J. Dairy Sci. 56:1033–1041. 310

Salama, A. A. K., G. Caja, X. Such, S. Peris, A. Sorensen, and C. H. Knight. 2004. 311

Changes in cisternal udder compartment induced by milking interval in dairy 312

goats milked once or twice daily. J. Dairy Sci. 87:1181–1187. 313

Such, X., G. Caja, and L. Pérez. 1999. Comparison of milking ability between 314

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N. P. Zervas, Wageningen Pers., Wageningen, The Netherlands. 317

318

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Table 1. Milk yield and milk composition of goats subjected to different oxytocin treatments.1 324

Experimental weeks

Parameter Treatment2 1 2 3 4 5 6 7 8 SEM

Control 2.13a 2.15a 2.05a 2.04a 2.05a 2.05a 1.98ab 1.84b 0.060

OT1 2.15a 2.10a 2.14a 2.08a 2.09a 2.05ab 2.03ab 1.92b 0.072 Milk yield (L/d)

OT2 2.04a 1.98a 1.95ab 2.06a 2.06a 1.95ab 1.85b 1.83b 0.055

Control 4.62 4.63 4.56 4.67 4.72 4.78 4.72 4.86 0.040

OT1 4.34 4.55 4.48 4.34 4.37 4.40 4.40 4.55 0.048 Fat (%)

OT2 4.42 4.44 4.52 4.60 4.48 4.68 4.75 4.76 0.037

Control 3.82 3.80 3.81 3.83 3.86 3.87 3.88 3.89 0.016

OT1 3.81 3.79 3.75 3.79 3.77 3.79 3.80 3.81 0.014 Protein (%)

OT2 3.88 3.83 3.84 3.88 3.86 3.89 3.92 3.93 0.013

Control 5.02 5.04 5.06 4.97 5.02 4.93 4.92 4.88 0.021

OT1 5.11 5.13 5.09 5.07 5.12 5.06 4.99 4.94 0.015 Lactose (%)

OT2 5.05 5.05 5.09 5.01 5.09 5.01 5.01 4.92 0.023

a–bMeans with different superscripts within the same row are different (P < 0.05). 325

1Data are estimated marginal means and standard error of means. 326

2Treatment: OT1 = endogenous oxytocin; OT2 = exogenous oxytocin. 327

328

329

330

331

332

333

334

335

336

337

338

339

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Table 2. Total milk volume and milk partitioning of goats injected with different doses of 340

oxytocin at 4-h milking intervals.1 341

Milking time (h)

Parameter Treatment 1200 1600 2000 SEM

Control 277.42 244.58 248.92 21.517

0.5 IU 264.17 278.17 329.83 13.037

1 IU 278.58 225.42 265.00 9.762

2 IU 285.00 263.83 290.42 14.550

Total milk

(ml)

4 IU 290.67 277.67 297.33 14.616

Control 82.48x 81.92x 87.94x 2.443

0.5 IU 53.95y 57.25y 59.13y 3.846

1 IU 49.64y 51.61y 53.87y 3.287

2 IU 52.06y 49.55y 48.97y 3.002

Machine

milk (%)

4 IU 40.21b,y 57.94a,y 61.69a,y 3.316

Control 17.52y 18.08y 12.06y 2.443

0.5 IU 46.05x 42.75x 40.87x 3.846

1 IU 50.36x 48.39x 46.13x 3.287

2 IU 47.94x 50.45x 51.03x 3.002

Residual

milk (%)

4 IU 59.79a,x 42.06b,x 38.31b,x 3.316

a–bMeans with different superscripts within the same row are different (P < 0.05). 342

x–yMeans with different superscripts within the same column for each item are different (P < 343

0.05). 344


346

347

348

349

350

351

352


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Table 3. Milk composition of machine milk and residual milk of goats injected with different 353

doses of oxytocin at 4-h milking intervals.1 354

Milking time (h)

Parameter Treatment 1200 1600 2000 SEM

Control 5.12a 4.22b 3.86b 0.125

0.5 IU 5.02a 4.00b 3.64b 0.139

1 IU 5.21a 4.33b 3.78b 0.223

2 IU 6.05a 4.62b 4.13b 0.170

Fat machine

milk (%)

4 IU 5.58a 4.02b 3.71b 0.170

Control 5.19a 4.67ab 4.26b 0.129

0.5 IU 4.83a 3.95b 4.00b 0.131

1 IU 5.78a 4.07b 4.38b 0.195

2 IU 5.83a 4.16b 4.46b 0.156

Fat residual

milk (%)

4 IU 5.55a 4.01b 4.18b 0.162

Control 2.87 2.98 2.81 0.075

0.5 IU 2.43 2.73 2.74 0.079

1 IU 2.64 2.97 2.77 0.078

2 IU 2.73 2.91 3.07 0.075

Protein

machine

milk (%)

4 IU 2.75 3.24 3.23 0.100

Control 3.16 3.41 3.40 0.112

0.5 IU 2.89 3.17 2.96 0.089

1 IU 2.86 3.39 3.17 0.086

2 IU 3.04 3.45 3.19 0.097

Protein

residual

milk (%)

4 IU 3.45 3.71 3.56 0.063

Control 4.48 4.55 4.59 0.029

0.5 IU 4.45 4.68 4.62 0.057

1 IU 4.52 4.68 4.73 0.042

2 IU 4.44 4.54 4.44 0.041

Lactose

machine

milk (%)

4 IU 4.50 4.41 4.45 0.045

Control 4.87 4.94 4.95 0.026

0.5 IU 4.79 4.89 4.91 0.036

1 IU 4.88 4.93 4.94 0.036

2 IU 4.83 4.89 4.94 0.032

Lactose

residual

milk (%)

4 IU 4.66 4.78 4.77 0.030

a–cMeans with different superscripts within the same row are different (P < 0.05). 355


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17

Table 4. Milk yield, milk composition, and SCC of goats before (Day 0) and after (Day 1–3) 357

injecting different doses of oxytocin at 4-h milking intervals.1 358

Days

Treatment 0 1 2 3 SEM

Control 1.49a 0.95b 1.57a 1.55a 0.097

0.5 IU 1.85a 0.97b 1.77a 1.75a 0.054

1 IU 1.53a 0.96b 1.60a 1.55a 0.042

2 IU 1.72a 0.97b 1.73a 1.65a 0.077

Milk yield

(L/d)

4 IU 1.81a 0.98b 1.85a 1.73a 0.067

Control 4.17a 3.71b 3.24c,x 4.07ab 0.084

0.5 IU 3.80a 3.34b 3.15c,x 3.82a 0.108

1 IU 4.24a 3.45b 2.67c,y 3.98a 0.183

2 IU 4.37a 3.73b 2.70c,y 3.93ab 0.173

Fat (%)

4 IU 4.25a 3.32b 2.65c,y 3.95a 0.221

Control 2.86b 3.31a 3.31a,y 3.16ab,y 0.059

0.5 IU 2.58c 3.23ab 3.28a,y 2.87bc,y 0.072

1 IU 2.78c 3.24b 3.50a,y 3.18b,y 0.127

2 IU 2.77c 3.25b 3.57a,xy 3.37ab,xy 0.148

Protein (%)

4 IU 3.05c 3.53b 3.82a,x 3.77ab,x 0.137

Control 4.56 4.69 4.75 4.79 0.042

0.5 IU 4.66 4.77 4.76 4.69 0.026

1 IU 4.71 4.81 4.88 4.88 0.022

2 IU 4.61 4.79 4.88 4.81 0.040

Lactose (%)

4 IU 4.59 4.64 4.65 4.62 0.035

Control 6.25a,x 6.15a,x 5.88b,x 5.88b,y 0.035

0.5 IU 6.24x 6.31x 6.14x 6.33x 0.050

1 IU 5.42y 5.68y 5.39y 5.34z 0.054

2 IU 6.16x 6.51x 6.00x 6.05xy 0.039

SCC (log/ml)

4 IU 6.20x 6.28x 5.91x 6.10xy 0.045

a–cMeans with different superscripts within the same row are different (P < 0.05). 359

x–yMeans with different superscripts within the same column for each item are different (P < 360

0.05). 361


363

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Study of mammary tight junction permeability in dairy goats traditionally milked

once a day

A. Torresa, N. Castrob, A. Suárez-Trujillob, A. Argüellob, and J. Capotea*

aInstituto Canario de Investigaciones Agrarias (ICIA), La Laguna 38200, Tenerife,

Spain

bDepartment of Animal Science, Universidad de Las Palmas de Gran Canaria, Arucas

35413, Spain.

*Corresponding author: Juan Capote, ICIA, Apto. de correos 60, La Laguna 38200,

Tenerife, Spain.

Tel.: +34 922542800; fax: +34 922542898. E-mail address: [email protected]

ABSTRACT

Effects of milking interval on mammary tight junction permeability are well-

documented in ruminants. However, the most studies have been focused in animals that

usually are milked twice a day. For this reason, thirty-two dairy goats in mid lactation of

two breeds traditionally milked once a day (Majorera, Palmera) and two parity numbers

(primiparous, multiparous) were used to evaluate the short-term effects of different

milking intervals (10, 14, 24, 28, and 32 h) on tight junction permeability of mammary

epithelia. Milk samples were analyzed for determination of chemical composition, and

Na and K concentrations. Blood samples were immediately taken after each milking and

analyzed for determination of lactose, and Na and K concentrations. Milk volumes

increased when milking interval was increased. On average, it increased from 2.23 to

2.73 L in Majorera, and from 1.38 L to 1.63 L in Palmera goats, at 24- and 32-h of milk

accumulation, respectively, which demonstrated the adaptation of the studied breeds to

accommodate greater milk volumes into the udder at extended milkings. Furthermore, it


126

did not produce apparent changes in the milk composition from 24- to 28-h, and from

24- to 32-h intervals. The concentrations of Na and K in milk and blood did not reflect

the degree of permeability of tight junctions at extended milkings, at least in goats

traditionally milked once a day. Finally, plasma lactose increased sharply at 24-h, being

more pronounced in primiparous (from 65.59 to 111.81 μM, at 14- and 24-h,

respectively) than multiparous goats (from 161.67 to 241.95 μM, at 14- and 24-h,

respectively), indicative of an increase in the permeability of tight junctions.

1. Introduction

Tight junctions form the continuous intercellular barrier between epithelial cells,

which is required to separate tissue spaces and regulate selective movement of small

molecules and ions across the epithelium (Anderson and Van Itallie, 2009). In the

mammary gland, the tight junctions are dynamic structures between the blood, or more

precisely the interstitial fluid (basolateral side), and milk in the alveolar lumen (apical

side), thus preventing serum components from entering into milk and vice versa

(Stelwagen et al., 1995). In addition, tight junctions are instrumental in maintaining the

polarized state of secretory cells, and keeping a difference in lipid and protein

composition between the basal and apical side of the plasma membrane (Stelwagen et

al., 1998).

In the mammary epithelium, tight junctions are formed during lactogenesis, prior

to onset of copious milk secretion, and are leaky during mammary involution (Nguyen

and Neville, 1998; Ben Chedly et al., 2010). During lactation the tight junctions are

become impermeable in most lactating animals, including ruminants. However,

systemic and local factors, such as changing hormone concentration, intramammary

pressure and mastitis, have been shown to regulate tight junction permeability

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(Stelwagen et al., 1999b). Tight junctions switch to a leaky state after approximately 18

h of milk accumulation in cows (Stelwagen et al., 1997), after 20 h in sheep (Castillo et

al., 2008), and after 21 h in goats (Stelwagen et al., 1994). Moreover, Stelwagen et al.

(1994) have previously shown that a decrease in the rate of milk secretion is correlated

with the leakiness of mammary tight junctions observed during extended milking.

However, Ben Chedly et al. (2013) found that the decrease in milk yield that occurs

during once daily milking in goats is due to regulation of synthetic activity rather than

to apoptosis of mammary epithelial cells or the state of the mammary gland tight

junctions.

The Na and K balance between the alveolar lumen and the interstitial fluid is

conditioned by tight junction integrity. Thus, Na and K can freely cross the apical

membrane, and the changes in the concentrations of these ions lead to corresponding

intracellular changes (Stelwagen et al., 1999a). Furthermore, lactose is a component

synthesized only in the mammary gland and is not secreted basolaterally in significant

quantities, so its presence in blood can only be explained by its movement from milk

into blood via leaky tight junctions (Stelwagen et al., 1994; Castillo et al., 2008).

Knowledge about how different milking intervals affect the permeability of tight

junctions in dairy goats traditionally milked once a day is required. For this reason, the

objective of this study was to evaluate some indicators of leakiness of tight junction at

different milking intervals in two dairy goat breeds traditionally milked once a day.

2. Material and methods

The experimental animal procedures were approved by the Ethical Committee of

the Universidad de Las Palmas de Gran Canaria (Arucas, Spain). The present study was

performed in the experimental farm of the Instituto Canario de Investigaciones Agrarias


128

(Tenerife, Spain) on 32 dairy goats belonging to two breeds: Majorera (n = 8,

primiparous, 2.09 ± 0.53 L/d; n = 8; multiparous, 2.11 ± 0.57 L/d), and Palmera (n = 8,

primiparous, 1.35 ± 0.39 L/d; n = 8; multiparous, 1.41 ± 0.20 L/d), in mid lactation at

the beginning of the experiment. The animals were fed according to the guidelines of

the Institute National de la Recherche Agronomique (INRA, Paris, France) and

recommendations (Jarrige, 1990). The goats were divided in 2 flocks (n = 16) balanced

for parity (primiparous and multiparous) and breed (Majorera and Palmera) with similar

milk yields.

The experiment considered 4 milking intervals (Flock 1: 10, 14, 24, and 28 h;

Flock 2: 10, 14, 24, and 32 h), where milk and blood samples were taken for analysis.

Goats were milked in a double 12-stall parallel milking parlor (Alfa-Laval, Madrid,

Spain) equipped with recording jars (4 L ± 5%) and a low-line milk pipeline. Milking

was performed at a vacuum pressure of 42 kPa, a pulsation rate of 90 pulses/min, and a

pulsation ratio of 60/40 in accordance with Capote et al. (2006). The milking routine

included wiping dirt off teat ends and stripping 2-3 squirts of milk from each teat,

machine milking and stripping milking, done by the operator to remove the milk

remaining in the udder before cluster removal, and teat dipping in an iodine solution

(P3-cide plus, Henkel Hygiene, Barcelona, Spain).

Milk volumes were recorded by using the recording jars in the milking parlor.

Milk samples were analyzed for determination of chemical composition, and Na and K

concentrations. Blood samples were immediately taken after each milking and analyzed

for determination of lactose, and Na and K concentrations. Milk fat, protein and lactose

percentages were determined by using a DMA2001 Milk Analyzer (Miris Inc., Uppsala,

Sweden). Concentrations of Na and K in milk were determined using atomic absorption

spectrometry (AAnalyst 200 spectrometer, Perkin-Elmer, Norwalk, USA) in the

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Laboratory of Chemical Analysis of the Instituto Canario de Investigaciones Agrarias,

and the concentrations of these ions in blood were measured by means of ion selective

electrodes (Olympus AU2700 analyzer, Beckman Coulter, Tokyo, Japan) in the

Laboratory LGS Análisis. The enzymatic assay for determination of plasma lactose

(Boehringer Mannheim / R-Biopharm) was based on two reactions, one measuring

galactose and the other measuring lactose and galactose; the difference between the two

provided a measurement of lactose concentration. This analysis was conducted in the

Laboratory of Research Unit at University Hospital (Tenerife, Spain).

The statistical analyses were performed by using SPSS 15.0 software (SPSS

Inc., Chicago, USA). Repeated measures analysis of variance (ANOVA), with

adjustments for non-sphericity (Greenhouse-Geisser correction), was applied to evaluate

milking intervals effects on studied parameters; followed by LSD post-hoc tests.

Differences among experimental groups (Majorera-primiparous, Majorera-multiparous,

Palmera-primiparous, Palmera-multiparous) were evaluated using a multiple

comparison test following the Tukey method. Statistical differences were considered

significant at P < 0.05. Data are presented as least squares means.

3. Results

Milk volume (Table 1) was affected due to milking interval in both experimental

flocks (P < 0.05). However, Majorera and Palmera goats did not show differences from

10- to 14-h of milk accumulation, but a significant increase was observed from 14- to

24-h intervals in the studied groups. In the Flock 1, milk volume at 28-h was higher

than milk volume at 24-h in the studied breeds, but these differences were not

significant (P > 0.05). In contrast, the goats of Flock 2 showed a dramatic increase in

milk volume in Majorera primiparous (17%), Majorera multiparous (27%), Palmera


130

primiparous (20%), and Palmera multiparous (10%) from 24- to 32-h of milk

accumulation. Regarding breed effect, no significant differences were found between

Majorera and Palmera goats at 10-h milking interval. Nevertheless, Majorera goats had

higher milk volumes than Palmera goats at subsequent milking intervals (P < 0.05).

Additionally, milk volumes were similar (P > 0.05) between primiparous and

multiparous goat at different milking intervals.

Milk fat percentages (Table 1) were comparable between consecutive milking

intervals (P > 0.05), except for goats of the Flock 1, where milk at 14-h contained lower

percentages of fat than milk at 24-h (P < 0.05). Nevertheless, there was a trend to obtain

milk richer in fat content when the milking intervals differ by more than 14 hours (P <

0.05). In addition, fat percentage was not affected by breed and parity factors, both in

goats of Flock 1 and 2 (P > 0.05).

No significant differences were detected in milk protein percentages from 10- to

14-h milking intervals in the studied groups (Table 1). Subsequently, Majorera breed

had an increase in protein content when interval switched from 14- to 24-h (P < 0.05),

and stayed stable from 24- to 28- and 32-h (P > 0.05). Likewise, Palmera goats did not

have differences in protein content from 24- to 28- and 32-h. Breed and parity had not

effects on milk protein percentage at the studied milking intervals.

No differences were found in milk lactose percentages in the studied goats

(Table 1) when the milking interval and breed factors were considered (P > 0.05).

Regarding parity effect, Palmera primiparous had higher values than Palmera

multiparous at 28- and 32-h (P < 0.05). However, these differences were not significant

between Majorera primiparous and multiparous.

Milking interval did not modify Na content in milk for Majorera goats (Table 2).

Only a slight increase in Na concentration was observed for Palmera primiparous and

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multiparous (Flock 2) from 10- with respect to 24- and 32-h. In general, primiparous

goats had lower levels of Na than multiparous goats, whereas Palmera had higher values

than Majorera of these ions in milk, when the parity and breed effects were considered,

respectively. Moreover, no changes were found in concentration of K in milk for the

goat groups due to milking interval, breed or parity factors (P > 0.05).

Goat breed and parity did not affect (P > 0.05) Na and K concentration in

plasma blood at all intervals (Table 2). Besides, as milking interval increased,

concentration of Na in blood plasma decreased for Majorera and Palmera in both

parities (P < 0.05). Otherwise, concentration of K in blood plasma was steady until 28-h

(Flock 1) and increased markedly at 32-h (Flock 2) for all goat groups.

Milking interval affected (P < 0.05) lactose concentration in plasma (Table 2). It

was observed that after 14-h interval, Majorera and Palmera goats in both parities

dramatically increased its levels of lactose in plasma blood. Likewise, parity factor had

an effect on plasma lactose, where primiparous goats exhibited lower values than

multiparous goats at the studied milking intervals. Finally, no differences were observed

between Majorera and Palmera breeds at the different intervals (P > 0.05).

4. Discussion

The increases in milk volume with increasing milking intervals, is a

consequence of a wider cisternal capacity of the studied breeds, which allowed a

continuous drop of milk from alveoli to the cistern, reducing the feedback inhibitor

process, the alveolar milk stasis and alveolar pressure (McKusick et al., 2002; Torres et

al., 2013a). Typically in goats, 24-h of milk stasis is necessary to activate regulatory

mechanisms leading to disruption of tight junctions and reduced milk secretion, longer

than the 18 h required to induce a similar phenomena in cows and sheep (Marnet and


132

Komara, 2008). Goats have a higher proportion of milk in their cistern than ewes or

cows, which most likely contributes to their ability to better maintain milk yield under

extended milking (Silanikove et al., 2010).

Disruption of mammary tight junctions is associated with a decrease in milk

yield due to longer milking intervals (Stelwagen et al., 1994; Delamaire and Guinard-

Flament, 2006), which is related with cell death and a decrease in mammary activity

(Ben Chedly et al., 2010). It is predicted that for milking intervals of less than 20-h in

goats and 18-h in cows, the concentration of β-casein f(1–28), peptide that serves as a

local regulator on milk secretion, would be higher in the cistern than in the alveoli

(Silanikove et al., 2000). Therefore, the alveoli will not be exposed to the full impact of

the negative feedback signal of this peptide. Extending milk stasis beyond these times

exceeds the storage capacity of the cistern, resulting in the equilibration of β-casein f(1–

28) concentration between the cistern and the alveoli, and inducing disruption of the

tight junction (Silanikove et al., 2010).

The higher volume of milk found for Majorera goats compared with Palmera

goats is due to cisternal size of each breed. Previously, Torres et al. (2013a) reported

that Majorera have higher udder depth values (difference in distance between the udder

floor and the cistern floor) than Palmera, which is correlated with the udder volume

(Capote et al., 2006). Bruckmaier et al. (1997) explained that a large absolute cisternal

volume implies that a large fraction of the milk is stored within the cisternal cavities.

Castillo et al. (2008) showed a greater milk accumulation rate in Lacaune than in

Manchega ewes, where Lacaune breed have a greater cisternal area than Manchega

breed (Rovai et al., 2008).

Milk volume in multiparous goats was higher than primiparous goats, but the

statistical differences were no significant, which was unexpected. Goetsch et al. (2011)

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reported that milk production is lower for primiparous than for multiparous dairy goats.

Salama et al. (2004) found that the differences in storage capacity of the cisterns

between primiparous and multiparous goats were more evident after 24 h of milk

accumulation, in which multiparous goats had larger cisternal area and were able to

store more volume of milk in the cistern than primiparous goats. McKusick (2000)

found that ewes with high milk volume-intramammary pressure ratio had a significant

degree of compliance in their udders because they were able to accommodate an

increase in intramammary pressure of 30% when the milking interval was extended to

24 h. Therefore, intramammary compliance or elasticity plays a significant role to

accommodate the milk volumes secreted. The results obtained could be explained by the

fact that primiparous goats had an optimal intramammary compliance due to adaptation

of the breed to once daily milking. However, further studies are needed to verify this

hypothesis.

Milk fat percentages had a trend to be higher as milking interval increased.

However, McKusick et al. (2002) and Castillo et al. (2008) in ewes, and Ayadi et al.

(2004) in cows observed that milk fat content decreased with longer milking intervals.

These authors indicate that there was transfer of milk fat from the alveoli to the cistern

during early udder filling, but this transfer was no longer taking place during the later

intervals. It has been reported an upward movement of the fat globules, in the opposite

direction to the downward draining and newly secreted milk at extended milking in

dairy cows (Ayadi et al., 2004). Conversely, this cistern recoil phenomenon did not

occur in goats, where once milk is ejected, it is unable to return to the alveoli (Salama et

al., 2004). In addition, Komara et al. (2009) in Alpine goats and Torres et al. (2013b) in

Majorera and Palmera goats did not find differences in fat percentages between once

and twice daily milking. Moreover, according to Stelwagen et al. (1997), the diameter


134

of milk fat globules is greater than the intercellular joints, and Komara et al. (2009)

found that fat globule size between once and twice daily milking were similar for dairy

goats. Therefore, changes in fat content according to milking interval are related to the

regulatory mechanisms for secretion of large and high-viscosity milk fat globules

relative to the components in the aqueous phase of milk (Davis et al., 1999).

Milk protein percentages did not have changes at extended milking in the

studied breeds, which agrees with observations in dairy cows by Ayadi et al. (2004) and

dairy ewes by Castillo et al. (2008), where protein content in milk was constant after 12

h. However, McKusick et al. (2002) found an increase in milk protein fraction from 20

h in dairy ewes. The tendency of protein content to increase for extended milking

intervals in some species or breeds may be explained by increased tight junction

leakiness allowing serum protein entering into the milk, since casein does not move

through leaky mammary tight junction (Ayadi et al., 2004; Castillo et al., 2008).

However, typical milk albumin concentration (the greatest potential contributor of

serum protein to milk) is too small to make an effect on protein concentration in milk,

being produced and secreted by mammary epithelial cells into milk (Silanikove et al.,

2013). Therefore, the changes in milk protein content according to milking interval, like

milk fat content, seems are more correlated to regulation of synthetic activity of

secretory cells or hydrolysis of protein rather to disruption of the mammary gland tight

junctions (Ben Chedly et al., 2013).

The absence of differences in milk lactose percentages found in the studied goats

according to milking interval factor is related with the udder size. Thus, Castillo et al.

(2008) reported a decrease in lactose content from the 20- to 24-h milking interval in

Manchega ewes (small udder cisterns), but not in Lacaune ewes (large udder cisterns).

Decreases of milk lactose percentage seem to be due to lactose passing from milk into

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blood through impaired tight junctions associated with extended milking intervals

(Stelwagen et al., 1994). However, Ben Chedly et al. (2013) proposed that the reduction

of milk lactose yield is essentially due to a reduction of its synthesis by the mammary

gland.

In general, Na and K contents in milk were not affected by the studied milking

intervals. Only a slight increase was observed in Na content for Palmera goats from 10-

to 24- and 32 intervals. When the permeability of tight junctions increases, the

concentration of Na in milk increases, and the concentration of K decreases (Stelwagen

et al., 1999a). Furthermore, a reduction of Na content and an increase of K content in

blood plasma would be expected during the disruption of tight junctions. In the present

experiment was detected the diminution of Na values in blood plasma in the studied

groups when the milking interval was increased, and the concentration of K only was

increased both Majorera and Palmera goats at 32-h interval. Castillo et al. (2008) did

not find differences in Na and K concentration in milk in Lacaune ewes at extended

milking intervals, but Manchega ewes had an increase of Na and a decreased of K in

milk after 20 h. These authors suggested that variations in ion concentration have a

relationship with the adaptation to extended milking intervals of these breeds being

lower in Manchega than Lacaune ewes. Furthermore, Stelwagen et al. (1994) found that

Na concentration in milk increased from 16.3 mM at 0 h to 21.3 mM at 36 h, and the K

concentration in milk decreased from 46.7 mM at 0 h to 34.3 mM at 36 h in Saanen

goats, as consequence of tight junction disruption. In the present study, Majorera and

Palmera breeds are fully adapted to once daily milking, which can explain that

concentrations of Na and K were not the best indicators of leakiness of tight junctions.

Despite the high variability of plasma lactose concentration obtained in the

experimental groups, this increased sharply at 24-h, indicative of an increase in tight


136

junction permeability. Castillo et al. (2008) considered that lactose in plasma is the main

indicator of mammary tight junction permeability, because changes in Na and K

concentrations may reflect an alteration in the transport of these ions across transcellular

rather than paracellular pathways. In Saanen goats, Stelwagen et al. (1994) showed an

increase of plasma lactose concentration after 21 h of milk accumulation, whereas that

in dairy cows, Stelwagen et al. (1997) observed the increase of lactose in plasma after

18 h of milk stasis. In addition, some studies which switched from twice to once daily

milking in goats and cows (Stelwagen et al., 1997; Ben Chedly et al., 2013)

demonstrated that the increase in blood lactose concentration is transient, suggesting

that the gland gradually adapted to once daily milking. Finally, the increases of plasma

lactose seem to have not been conditioned by breed effect. Nevertheless, primiparous

goats had an increase more pronounced in plasma lactose values than multiparous goats

at extended milking intervals, although these animals presented the highest

concentrations, which may indicate that the older animals had a greater degradation in

the integrity of tight junction due to different lactations. On the other hand, Castillo et

al. (2008) found that Manchega ewes increased by 5-fold its plasma lactose values from

20- to 24-h, whereas Lacaune ewes increased by only 1.5-fold, indicating that the tight

junction leakiness effect was greater in Manchega that in Lacaune ewes. Therefore, the

udder development plays an important role on degree of tight junction leakiness.

5. Conclusions

The wide cisternal capacity of the Majorera and Palmera breeds allowed an

increase in milk yield above to 24 h of milk accumulation. Furthermore, milk

composition was not impaired when milking intervals were increased until 28 or 32 h.

In regard to indicators of leakiness of tight junction, the concentrations of Na and K in

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milk and blood did not reflect its degree of permeability, at least in goats traditionally

milked once a day. Moreover, the increase in the concentration of plasma lactose after

14 h did not allow to precise whether the disruption of tight junctions occurred before or

after to 24 h, or simply is normal flux of lactose from apical to basolateral side due to

status of tight junctions in goats usually milked once time a day. Therefore, a milking

interval between 14- and 24-h will be necessary to take into consideration to evaluate

the integrity of tight junctions. Nevertheless, the results did not show a clear

relationship between the milk yields and damages of tight junction permeability, which

is interesting to develop breeding programs adapted to extended milkings, in areas that

require it.

Conflict of interest

None.

Acknowledgments

This work was supported by Fondo Europeo de Desarrollo Regional-Instituto

Nacional de Investigación y Tecnología Agraria y Alimentaria (FEDER-INIA)

RTA2009-00125. The authors are also grateful to Dr. Eduardo Salido and Dr. Ana Rosa

Socorro for their assistance with the experimental procedures.

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142

Table 1. Effects of milking interval on milk volume and milk composition in two dairy

goat breeds 1

Flock 1 Flock 2

Milking interval (h) Milking interval (h)

10 14 24 28 SEM

10 14 24 32 SEM

Milk volume (L)

Majorera primiparous 1.02a 1.40a,y 1.81b,y 2.05b,y 0.157 0.98a 1.31a,xy 2.23b,y 2.61c,y 0.208

Majorera multiparous 1.04a 1.31a,y 2.03b,y 2.18b,y 0.176 1.21a 1.50a,y 2.24b,y 2.84c,y 0.198

Palmera primiparous 0.61a 0.71a,x 1.11b,x 1.35b,x 0.155 0.64a 0.80a,x 1.20b,x 1.44c,x 0.128

Palmera multiparous 0.72a 1.03a,xy 1.45b,xy 1.76c,xy 0.116 0.72a 1.00a,xy 1.55b,x 1.71c,x 0.108

Milk composition

Fat (%)

Majorera primiparous 2.17a 2.55a 3.15b 3.66b 0.189 2.27a 2.25a 2.83ab 3.05b 0.113

Majorera multiparous 2.95a 3.24a 4.11b 4.38b 0.187 2.99a 2.89a 3.19ab 3.61b 0.118

Palmera primiparous 2.41a 2.45a 3.72b 3.56b 0.225 2.69a 2.88ab 3.64b 3.37b 0.134

Palmera multiparous 2.43ª 3.03a 3.92b 4.22b 0.207 2.39a 2.95ab 3.51bc 3.83c 0.173

Protein (%)

Majorera primiparous 2.39a 2.73a 3.19b 3.39b 0.156 2.19a 2.38a 3.03b 3.02b 0.118

Majorera multiparous 2.89a 2.89a 3.84b 4.30b 0.205 2.49a 2.75a 3.08b 3.40b 0.142

Palmera primiparous 2.37a 3.01ab 3.73b 3.54b 0.176 2.32a 2.82ab 3.19bc 3.73c 0.173

Palmera multiparous 2.97a 3.07a 3.98b 4.01b 0.180 2.41a 3.04ab 3.36bc 3.87c 0.165

Lactose (%)

Majorera primiparous 5.06 4.95 4.73 4.69xy 0.124 5.51 5.45 5.05 5.08xy 0.085

Majorera multiparous 4.67 4.43 4.55 4.38x 0.082 4.98 5.09 4.83 4.75x 0.109

Palmera primiparous 5.33 5.08 4.76 5.03y 0.070 5.35 5.17 5.06 5.22y 0.087

Palmera multiparous 4.53 4.81 4.39 4.20x 0.136 4.94 5.04 4.77 4.80x 0.098

a–cMeans with different superscripts within the same row are different (P < 0.05).

x–yMeans with different superscripts within the same column for each item are different (P < 0.05).

1Data are least square means and standard error of means.

MANUSCRITO 5

143

Table 2. Effects of milking interval on concentration of Na and K in milk and plasma

blood and concentration of plasma lactose in two dairy goat breeds 1

Flock 1 Flock 2

Milking interval (h) Milking interval (h)

10 14 24 28 SEM

10 14 24 32 SEM

Milk

Na (mM)

Majorera primiparous 12.38x 13.47x 14.80x 14.99x 0.437 12.65x 14.13x 13.99x 13.33x 0.605

Majorera multiparous 18.62y 17.43y 18.17xy 19.87y 0.519 20.03y 18.74y 21.99y 20.76y 0.996

Palmera primiparous 12.53x 14.36xy 15.99x 15.41x 0.538 13.78a,x 15.56ab,xy 16.51b,x 17.02b,xy 0.880

Palmera multiparous 19.76y 22.36y 22.17y 24.36z 0.763 17.70a,y 18.29ab,y 20.87b,xy 21.28b,y 0.620

K (mM)

Majorera primiparous 34.75 37.44 37.02 37.15 0.904 35.70 39.82 38.07 38.53 0.960

Majorera multiparous 36.01 38.80 42.80 39.96 1.149 38.13 41.99 40.98 40.24 0.728

Palmera primiparous 34.16 36.99 34.51 35.57 0.805 33.35 36.33 35.13 33.20 0.536

Palmera multiparous 33.36 35.76 37.44 34.02 1.131 34.65 36.32 37.93 36.44 0.839

Plasma blood

Na (mM)

Majorera primiparous 146.08b 145.55b 144.68a 144.23a 0.278 145.95b 145.30b 144.05a 143.90a 0.287

Majorera multiparous 148.53c 146.95bc 146.80ab 144.90a 0.517 146.88b 146.05ab 144.15a 144.45a 0.417

Palmera primiparous 146.45b 144.85ab 142.70a 142.75a 0.552 147.28b 145.93ab 143.85a 143.80a 0.455

Palmera multiparous 147.05b 145.20ab 144.18a 143.33a 0.464 147.00c 145.50bc 143.80a 144.40ab 0.365

K (mM)

Majorera primiparous 5.18 5.08 5.00 5.73 0.120 5.10a 4.78a 4.73a 5.88b 0.148

Majorera multiparous 5.23 5.03 4.90 5.45 0.102 5.28ab 4.93a 4.60a 5.90b 0.165

Palmera primiparous 5.33 5.05 4.95 5.53 0.134 5.03ab 4.90a 4.55a 5.45b 0.117

Palmera multiparous 4.93 5.10 4.88 5.63 0.136 4.68a 4.58a 4.43a 5.58b 0.134

Plasma lactose (μM)

Majorera primiparous 54.96a,x 66.51a,x 127.85b,x 181.05c,y 14.435 65.48a,x 84.39b,xy 140.98c,x 230.23d,y 17.707

Majorera multiparous 135.45a,y 177.23a,y 235.51b,y 328.22c,z 20.651 120.64a,y 180.95a,z 222.92b,y 308.96c,z 21.158

Palmera primiparous 44.26a,x 56.26a,x 88.73b,x 110.38c,x 10.100 43.28a,x 55.18a,x 89.71b,x 152.78c,x 12.528

Palmera multiparous 136.75a,y 160.35a,y 264.00b,y 342.21c,z 22.518 106.96a,y 128.15a,y 245.37b,y 314.44c,z 22.815

a–dMeans with different superscripts within the same row are different (P < 0.05).

x–zMeans with different superscripts within the same column for each item are different (P < 0.05).

1Data are least square means and standard error of means.

CONCLUSIONES

CONCLUSIONES

147

Artículo 1Elhechodequealrededordel80%delalechetotalqueseencuentraenlaubre,sealmacene

enloscompartimentoscisternales,tantoalas14-comoalas24-h,sugierequelamayorpartedela

transferencia de leche desde los alvéolos a la cisterna ocurre durante las primeras fases de llenado

delaglándula.Poresarazónnoseencontrarondiferencias,enrelaciónalacomposiciónquímicade

la leche cisternal, entre ambos intervalos de ordeño. Sin embargo, los diversos cambios que presen-

taron los contenidos de grasa, lactosa y sólidos totales en la leche alveolar, sugieren la necesidad de

posteriores estudios sobre los mecanismos responsables de la eyección de la leche entre ordeños.

Artículo 2Los resultados demostraron que la práctica del doble ordeño no mejora la producción de

lecherespectoaunordeñodiarioenlascabrasderazaMajorerayTinerfeña,locualesdeinterés

para los sistemas de producción caprina, en donde se busca reducir los costes relacionados con la

producción de leche. No obstante, el aumento significativo en la producción lechera que mostraron

lascabrasderazaPalmeraalordeñardosvecesaldía,sugierequepodríaserunaprácticarentable

en ciertos momentos de la lactación. Sin embargo, el contenido de proteína en leche no incrementó

en concordancia con la producción. Por esta razón, se necesitan otros estudios para evaluar los

efectos de la frecuencia sobre el rendimiento quesero, lo cual es un aspecto de suma importancia en

la economía ganadera de Canarias. Además, el conocimiento de las estructuras de fraccionamiento

de leche puede servir de base para futuros programas de selección, al objeto de mejorar la facilidad

de ordeño en las razas locales.

Manuscrito 3Los cambios a corto plazo de la frecuencia normal de ordeño en cabras tradicionalmente or-

deñadas una vez al día durante la lactancia temprana puede afectar la producción de leche en cabras

derazaMajorera,comolodemuestraelincrementosignificativocuandosecambiadeunoadosor-

deños diarios. Sin embargo, las variaciones en el contenido de grasa y perfil proteico requieren estu-

dios acerca de cómo éstas afectan la producción y calidad de los quesos, ya que la finalidad principal

delasexplotacionescaprinascanariaseslafabricacióndeeseproducto.Porotrolado,lafaltade

incremento en la producción durante el triple ordeño, con la disminución en los porcentajes de grasa

en la leche, hace necesario futuros estudios para evaluar las causas que provocan este descenso.


148

Manuscrito 4La liberación de oxitocina por estimulación previa al ordeño y la administración de oxitocina

sintética no tuvo efecto galactopoyético ni cambios aparentes en la composición química de la leche

en cabras no ordeñadas inmediatamente que tradicionalmente se ordeñaban una vez al día. Además,

la ausencia de diferencias en el fraccionamiento lechero y composición de la leche entre la admi-

nistración de cuatro dosis de oxitocina indica que la contracción de las células mioepiteliales que

rodean los alvéolos es similar en respuesta a bajas y altas dosis de esta hormona.

Manuscrito 5LaampliacapacidadcisternaldelascabrasderazaMajorerayPalmerapermitióunaumento

delaproduccióndelechedespuésde24hdeacumulación.Además,lacomposiciónquímicadela

lechenosevioafectadacuandolosintervalosdeordeñoseincrementaronhasta28o32h.Enloque

se refiere a los indicadores de permeabilidad de las uniones celulares del epitelio mamario, las con-

centraciones de Na y K en leche y sangre no reflejaron un mayor grado de permeabilidad, al menos

encabrastradicionalmenteordeñadasunavezaldía.Porotraparte,elaumentoenlaconcentración

delactosaenelplasmasanguíneo,despuésde14hdeacumulacióndeleche,nopermitióprecisar

silaroturadelasunionescelularesseprodujoantesodespuésde24h,osedebíaalflujonormalde

lactosa desde el lado apical al basolateral por el estado de dichas uniones en cabras acostumbradas

a largo intervalos de ordeño. Adicionalmente, los resultados no mostraron una relación entre los ren-

dimientos de leche y daños en la permeabilidad de las uniones celulares, lo cual es interesante para

el desarrollo de programas de selección, en las zonas que requieran intervalos de ordeño más largos.

efecto de la frecuencia de ordeño sobre la producción ... · ganadería caprina al sostenimiento...

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