Genetic improvement of meat sheep. 5. Heritability of post-weaning weight and gain in Dorset and Border Leicester sheep

The heritability of corrected post-weaning weight has been estimated for both Dorset and Border Leicester sheep and the heritability of corrected post-weaning gain and the repeatability of body weight for Dorset sheep. In the Dorsets, the half-sib heritabilities of corrected post-weaning weight were 0.36, 0.1 4 and 0.28 respectively for rams, ewes and pooled over sexes. The corresponding parent-offspring heritabilities were 0.17, 0.32 and 0.25 respectively. The half-sib heritabilities of corrected post-weaning gain were respectively 0.28, 0.21 and 0.32 and the corresponding parent-offspring estimates -0.31, 0.03 and -0.14. The repeatability of body weight was estimated as 0.64 for both sexes. In the Border Leicester, the half-sib heritability of corrected post-weaning weight was 0.26, 0.17 and 0.23 for rams, ewes and pooled over sexes respectively. The corresponding parent-offspring estimates were 0.09, 0.04 and 0.06. Heritabilities were estimated on a within-property basis and then pooled over properties. Two methods of pooling the half-sib heritabilities were compared: 1. pooling the sums of squares and cross products and degrees of freedom and 2, pooling by weighting each estimate by the inverse of its variance. Pooling by method 1. resulted in consistently higher estimates than did pooling by method 2. Reasons for this are discussed.