Genetic improvement of meat sheep. 3. Heritability of weaning weight of Dorset and Border Leicester sheep

The heritability of weaning weight, uncorrected and corrected by three different methods has been estimated from several Dorset properties and one Border Leicester property. The estimates varied greatly over properties. The half-sib heritabilities of uncorrected weaning weight exceeded those of all corrected weights in all properties but one and the reason was found to be non-random use of sires over the joining period. The pooled half-sib heritabilities of uncorrected weaning weight and weaning weight corrected by average daily gain, pooled regression and least squares were 0.27, 0.11, 0.15 and 0.18 respectively for the Dorsets and the corresponding estimates for the Border Leicester were 0.46, 0.20, 0.15 and 0.16 respectively. In the Dorsets the pooled heritabilities calculated by dam-offspring regression were 0.04, 0.06, 0.09 and 0.10 for uncorrecred weaning weight and weaning weight corrected by average daily gain, pooled regression and least squares respectively. There was no significant difference between the heritabilities of weaning weight corrected by least squares or pooled regression but the heritability of weaning weight corrected by least squares significantly exceeded that of weaning weight corrected by average daily gain.