Effects of sex and some environmental factors on weaning weight in sheep

Abstract

The effects of age at weaning, type of birth and rearing, age of dam and sex on weaning weight of lambs were investigated among 4876 Merino and 1221 Poll Dorset lambs over two years on 11 properties in Victoria. The regression coefficients of weaning weight on age at weaning varied considerably between properties. Lambs born and reared as twins were about 15 per cent lighter at weaning than single lambs, and lambs born as twins and reared as singles had about half the handicap. The average weaning weight of lambs increased with age of ewe up till five years and declined thereafter. Corrections to weaning weight for these effects are required for efficient selection. These corrections vary between years and properties. In most flocks there are inadequate numbers of sheep to determine accurate correction factors for each property each year and so standard corrections must be used.