Stocking rate, joining time, fodder conservation and productivity of Merino ewes. 2. Birth weight, survival and growth of lambs

Abstract

In an experiment at Hamilton in western Victoria, groups of 30 Merino ewes were stocked at 11.7, 15.4 or 19.2 ewes ha-1 and joined to Merino rams each year on April 5 or May 8 for five weeks. Hay was conserved on half the number of plots and fed back to the ewes before and during joining. Observations on birth weight, survival, and growth of lambs born between 1970-73 are presented. Both the highest stocking rate and the earlier lambing were associated with a depression of about 7 per cent in the birth weight of twin lambs, but single lambs had similar birth weights on all treatments. Lamb survival was highly variable and there were few significant treatment effects. However, mortalities within 48 hours of birth were lower amongst flocks joined to lamb in October than those lambing in September (single lambs 9.2 per cent vs. 14.7 per cent-twin lambs 19.9 per cent vs. 40.2 per cent). Most of the improvement was attributed to drier conditions and lower windspeeds in October. Lamb growth rates fell with increasing stocking rate but the variation in weaning weight was less than 2 kg. Lambs born in September were about 10 per cent heavier at weaning than those born in October. Compensatory growth after weaning resulted in negligible differences in weight at 12 months between lambs from the different stocking rate treatments, but lambs born in September were still significantly heavier than those born in October.