Ingestión de alimento, digestibilidad y cinética de tránsito en ovino lechero. Estudio comparativo entre ovejas Manchega y Lacaune

Se disenaron 2 exp. con ovejas Lacaune (LC) y Manchega (MN), para comparar la ingestion de MS (MSI), la digestibilidad, la cinetica de transito y el contenido digestivo, con el fin de explicar las posibles diferencias de ingestion. En el exp. 1, 10 ovejas MN y 10 LC gestantes, se estabularon durante las ultimas 10 semanas de gestacion. La MSI y MS digestible fueron superiores en las ovejas LC que en las MN. La raza no afecto a la digestibilidad, ni a la cinetica de transito ni al contenido del tracto digestivo. Los cambios de peso vivo (PV) y condicion corporal fueron similares. Por el contrario, los corderos LC tendieron a pesar menos que los MN, lo que sugiere diferencias geneticas entre razas en la utilizacion de la energia. La mayor ingestion observada en las LC podria estar relacionada con la mayor demanda energetica para el desarrollo de la glandula mamaria. En el exp. 2, 16 ovejas MN y 16 LC se estabularon las 12 primeras semanas de lactacion. La produccion de leche, el contenido de grasa y proteina, asi como la MSI y MS digestible fueron superiores en las ovejas LC que en las MN. Al avanzar la lactacion la MSI se mantuvo constante en las ovejas LC, mientras que en las MN disminuyo. A lo largo de este periodo las LC perdieron 0.5 kg de PV mientras que las MN ganaron 4.4 kg. La raza no afecto ni la digestibilidad, ni la cinetica de transito. El contenido total del tracto digestivo fue superior en las LC que en las MN. Los resultados sugieren que el esquema de seleccion de la raza LC, ha incrementado la produccion de leche junto con la ingestion voluntaria, estando esta ultima asociada a un incremento de la capacidad ruminal. La mayor produccion de leche de las LC no pueden atribuirse unicamente a la mayor MSI y otros factores son necesarios para soportar esta mayor produccion. Finalmente, se compararon 6 modelos matematicos con el fin de seleccionar el que mejor describia el tiempo de retencion de dos marcadores, Cr2O3 y Co-EDTA. Se utilizaron los datos de los experimentos 1 y 2. Las curvas de excrecion de cromo y cobalto se ajustaron a un modelo compartimental (M1), dos modelos bicompartimentales tiempo independientes con tiempos de retencion distribuidos exponencialmente (M2 y M3), y tres modelos bicompartimentales tiempo dependientes con ordenes crecientes de gamma dependencia (M4, M5 y M6). Los modelos M1, M5 y M6 fueron los mejores ajustes para describir la cinetica de transito digestivo. Con el fin de averiguar si las estimaciones obtenidas utilizando marcadores son una buena expresion de los parametros reales, 8 ovejas se sacrificaron en la semana 5 y otras 8 en la semana 12 de lactacion. Antes del sacrificio, se les administraron 2 marcadores, Cr2O3 y Co-EDTA, para estimar los ritmos de paso en los compartimentos digestivos. Los ritmos de paso estimados con las curvas de excrecion fecal de Cr2O3 no representaron la cinetica digestiva del marcador obtenida con los datos de sacrificio, aunque la prediccion mejoro cuando se utilizo el Co-EDTA. Two experiments were carried out with pregnant and lactating dairy ewes, to compare dry matter intake (DMI), and total tract apparent digestibility, digesta kinetics and digestive tract content between Lacaune (LC) and Manchega (MN) sheep, to explain possible differences between both breeds in voluntary feed intake. In experiment 1, 10 MN and 10 LC single-bearing pregnant ewes, were permanently housed for the last 10 weeks of pregnancy. DMI and digestible DMI were higher in LC than in MN sheep. Breed did not affect total tract apparent digestibility, digesta kinetics or digestive content. Changes in body weight and body condition score were similar between breeds. In contrast, LC lambs tended to weigh less than MN lambs, suggesting genetic differences in the energy utilization between breeds in late pregnancy. Higher DMI observed in LC sheep could be related to higher energy demand for mammary development. In experiment 2, 16 MN and 16 LC lactating multiparous ewes, were permanently housed during the first 12 weeks of lactation. Milk, fat and protein yield as well as DMI and digestible DMI in LC ewes was higher than in MN ewes. DMI was constant in LC sheep with advancing lactation, while in MN sheep decreased. Throughout this period LC ewes lost 0.5 kg of body weight while MN gained 4.4 kg. Breed did not affect either apparent digestibility or digesta kinetics. The total tract digestive content was higher in LC than in MN sheep, particularly due to the reticulo-rumen. Results suggest that the scheme of selection in LC dairy sheep has increased milk yield together with voluntary feed intake, the latter being associated with an increase in the rumen fill capacity. Finally, the aim of the third study was to take a mathematical approach to select the best modelling method to estimate the outflow rates from external marker excretion curves in dairy sheep. Data from previous experiments were used as a source of marker excretion curves. Six mathematical models were compared. Faecal chromium and cobalt concentration curves were fitted with a multicompartmental model (M1), 2 two-compartment age-independent models with exponential distributed residences times (M2 and M3), and 3 two-compartment models with increasing order of gamma age dependency (M4, M5 and M6). The models M1, M5 and M6 proved to be the best fits for describing digesta kinetics in pregnant and lactating ewes. To ascertain whether the estimates obtained through the markers are a good expression of the real parameters, 8 lactating ewes were slaughtered at week 5 and 8 more at week 12 of lactation, Prior to slaughtering, two external markers were administered in order to estimate rates of passage of the reticulo-rumen and large intestine. Outflow rates estimated from faecal chromium excretion did not represent marker kinetics in the gut compartments obtained from slaughter data, but the prediction improved when the marker was Co-EDTA.