Improving the nutrition of Merino ewes during pregnancy and lactation increases weaning weight and survival of progeny but does not affect their mature size

Abstract

Lamb growth to weaning, and during the period immediately following weaning, influences post-weaning mortality and may affect mature size. The hypothesis tested in the experiments reported in this paper was that changes in the maternal liveweight of Merino ewes during pregnancy and lactation could predict the weight at weaning, post-weaning survival and mature size of their progeny. At two sites (Vic. and WA) in each of two years, a wide range in the liveweight profiles of ewes was generated during pregnancy and lactation by varying the amount of supplements fed and feed on offer grazed. Across the four experiments this resulted in progeny weights ranging from 13.8 to 28.3 kg just before weaning. Lamb growth was primarily related to the amount of feed on offer during lactation, but was also related to the liveweight change of the ewe during pregnancy. These relationships were consistent in both experiments at each site. Weaning weight was strongly associated with post-weaning survival at the Vic. site. Survival rates decreased significantly when weaning weights were below 20 kg. These results indicate that management of ewe and lamb nutrition to maximise growth of lambs before weaning and growing weaners at 30 g/day or more after weaning are important for optimal post-weaning survival. The findings also suggest that the mature size of offspring is unlikely to be adversely affected by pre-weaning nutrition within the range of nutritional scenarios during pregnancy and lactation that are likely to be experienced within the Australian sheep industry.