ÉVOLUTION DES QUANTITÉS D'ALIMENT INGÉRÉES PAR LES BREBIS A LA FIN DE LA GESTATION ET AU DÉBUT DE LA LACTATION. INCIDENCES SUR LEURS PERFORMANCES. I. — ÉTUDE DE DEUX RATIONS A BASE DE FOIN DE QUALITÉ DIFFÉRENTE

Abstract

Variation factors in the voluntary feed intake of ewes during late pregnancy (5 wk) and early lactation (5 wk) and their consequence on lamb health and growth were studied using diets containing meadow hay. The ewes were fed ad lib with hay of poor quality (experiment [exp.] 1: organic matter digestibility 49.5%) or moderate quality (exp. 2: organic matter digestibility 59.6%) and with a constant amount of concentrate feed (200 g during late pregnancy, 400 g during early lactation). The animals were housed in individual pens under open (exp. 1) or closed (exp. 2) sheds. Feed intake, weight gain and growth were measured in all the lambs. Milk yield was also recorded in some ewes as well as the plasma level of non esterified fatty acids. The voluntary intake of hay increased up to the 3rd wk prior to lambing. Thereafter it decreased until lambing, except in exp. 1 where the hay intake increased abruptly during the last week in relation to a large fall in the ambient temperature (between -5 and -15.degree. C). During the first 5 wk of lactation, the increase in the hay intake was slow (+ 17% as compared to the first week). A main factor of variation in the voluntary intake was the liveweight, with the heaviest ewes showing a tendency to eat more hay. The correlation coefficient between liveweight and hay matter intake ranged between 0.3-0.4 (P < 0.01). Another variation factor was the number of lambs born and suckled; ewes bearing 2 lambs tended to eat less hay during the last weeks of pregnancy than those bearing 1 lamb, especially in exp. 2. During lactation ewes nursing 2 lambs ate more hay than those nursing 1 lamb. A 3rd variation factor was ewe age; young ewes consumed more hay than the adult ewes, when the amounts ingested were expressed relatively to the metabolic weight. Paradoxically, hay quality, although very different in the 2 experiments, did not affect hay intake very much. The ambient temperature conditions varied between experiments due to the housing conditions. The weight gains of the ewes were 6.8 kg (exp. 1) and 4.4 kg (exp. 2) during the last 5 wk of pregnancy. During the first 5 wk of lactation, the weight losses were comparable for the 2 experiments and ranged about 4.5 kg. Although the hay quality did not affect the hay intake, milk production and lamb growth, especially in the case of twins, were reduced when they received hay of poor quality. The estimated metabolizable energy balance, the mobilization of body reserves, the probable effects of the ambient temperature and animal fatness are discussed in relation to litter size and hay quality.