Repeatability and heritability of fertility in hill sheep

Abstract

SUMMARY Lambing records of 3,500 Scottish Blackface ewes and 2,000 Welsh Mountain ewes were used for a study of repeatability of ewe fertility and litter size. The repeatability of litter size at birth (calculated as an intra-ewe correlation) was higher in both flocks (0.19 and 0.24 for Blackface and Welsh ewes respectively) than that for barrenness (0.09 and 0.08) or for number of lambs born per mating (0.07 and 0.10). Repeatability of the corresponding traits at weaning were generally about half these values. About two-thirds of the ewes had sires recorded and were used for a heritability analysis. The heritability of litter size at birth in both flocks was higher (0.14 and 0.16 for Blackface and Welsh respectively) than either the heritability of barrenness (−0.03 and 0.03) or of numbers of lambs born per mating (−0.01 and 0.07). It was concluded that the greatest improvement in numbers of lambs weaned would be obtained by selection on litter size at birth. There would be correlated changes in live-weight (genetic correlations of 0.44 and 0.78 for Blackface and Welsh respectively) but not in fleece weight (genetic correlations of 0.09 and −0.13).