The influence of time of lambing in south-eastern South Australia on the reproductive rate of the Merino ewe and on lamb survival and growth

Abstract

Merino flocks lambing in either autumn or winter in south-eastern South Australia showed no consistent differences in reproductive performance over a five-year period. The percentage of ewes that lambed, the level of twin births, and the lamb mortality rates varied in their relative contribution to the final result in any one season. For each reproductive factor measured the difference between the flocks varied from year to year in magnitude and sign. Lambs born in the winter had higher birth weights and better early growth rates, but liveweight during their first summer period was generally less than that of autumn born lambs. Survival rates in both groups were similar.