Genetic parameters for ewe rearing performance1

This paper reports genetic parameters for ewe performance traits in sheep breeders' flocks in New Zealand. Animal performance records from the AgResearch Lamb Survival Database and from Sheep Improvement Limited were used to generate data sets from 3 lambing years (2003 to 2005) in 24 flocks, and involving 31,651 ewes and many breeds and breed compositions (predominantly Romney, Coopworth, and Texel). The heritabilities and repeatabilities for the litter survival traits were very low. Litter weight traits had heritabilities ranging from 0.12 for BW of lamb weaned to 0.28 for total triplet litter weight at birth and repeatabilities ranging from 0.18 to 0.29. The repeatabilities of BCS and maternal behavior score were low to moderate. This study showed that there is little to be gained from including litter survival in sheep selection programs because heritabilities and repeatabilities for the litter survival traits were very low. However, genetic gains in BCS, maternal behavior score, litter weight at birth, and litter weight weaned are possible in this population. Incorporating these traits into sheep selection programs warrants investigation to improve ewe and therefore flock performance.