Nutrition of the pregnant ewe and its effect on gestation length, lamb birth weight and lamb survival
The nutrition of grazing, pregnant crossbred ewes was managed so that from 6-15 and from 15-20 weeks of pregnancy, ewes were offered either high (H) or low (L) quality and quantity of nutrition as provided by pasture. At one week prior to parturition, the ewes in each of the four treatment groups (HH, HL, LH, LL) were then placed onto good pasture for lambing. Differential nutrition during pregnancy significantly affected gestation length of the ewes, with HH ewes having the shortest gestation. By day 148, 1.6 times more HH ewes had lambed compared with the LL group ewes. Significant differences were observed in lamb birth weight5 with nutrition in the last trimester (15-20 weeks) having a greater influence on birth weight. This was particularly so for twins. There was no significant difference in the survival of the single lambs, but for twin lambs survival was lowest with the LL ewes. These results show the consequences of maintaining or altering nutrition of single- and twin-bearing ewes during pregnancy. Birth weight of twin-born lambs was most responsive. Apart from lambs of the LL group ewes, the weaning weights of surviving lambs were largely unaffected by prenatal nutrition to one week prepartum.