Some effects of live weight and body condition on the milk production of Blackface ewes

Abstract

SUMMARYApproximately 15 weeks before parturition, forty-eight pregnant Blackface ewes were divided into three similar groups. During the 15–6 weeks prepartum period the ewes were fed to increase the live weights and body condition scores of ewes in each of groups A and B and to decrease those of ewes in group C. At 6 weeks prepartum mean differences of approximately 11 kg live weight and two grades of body condition had been created. Food was rationed to the ewes in all groups per kg live weight based on their weights 6 weeks prepartum, to provide the theoretical requirements of Blackface ewes bearing twin lambs. All groups of ewes made similar live-weight gains in late pregnancy and the mean birth weights of the lambs were also similar. Blood plasma F.F.A. values confirmed that the ewes were similarly nourished in late pregnancy regardless of live weight or body condition. During lactation the ewes were fed 9·2 g D.O.M./kg based on their immediate post-partum live weights, plus an allowance for a predicted level of milk production. Ewes in groups A and C were fed 0·5 and ewes in group B, 0·25 g D.O.M. per g of predicted milk production. The ration was increased after the 1st and 2nd weeks of lactation, then maintained at a constant level for the remainder of lactation. Milk production of the ewes was measured using a lamb suckling technique during a 10-week lactation. The mean daily milk production of ewes in groups A and C were similar and the yield of each of these groups was substantially greater than that of group B ewes. The mean total milk production of ewes suckling twin lambs in groups A, B and C was 127, 108 and 142 kg respectively, and of ewes suckling single lambs 104, 81 and 91 kg respectively. The mean live-weight changes of ewes in groups A and C were similar during lactation. Except for group A ewes suckling single lambs, which maintained their mean live weight, all ewes lost weight in early lactation and consistent gains were not made until late lactation. Greatest live-weight loss occurred in group B ewes and extended further into lactation. Changes in body condition followed a similar course to live weight changes. The mean daily live-weight gain of twin lambs in groups A, B and C was 279, 275 and 284 g respectively, and of single lambs, 318, 300 and 319 g respectively. The evidence indicates that ewes in lean body condition have a higher efficiency of food conversion to milk and that in situations of continuous undernourishment a high state of body condition is undesirable during lactation.