Genetic improvement of meat sheep. 2. Correction of weaning weight in Dorset and Border Leicester sheep

Abstract

Data from 14635 Dorset and 1214 Border Leicester lambs from nine properties and five years were used to estimate the effects on weaning weight of age of lamb, sex, birth-rearing status and parity of dam, using three methods (average daily gain, pooled regression and least squares). Corrections for all effects varied greatly over properties and years, indicating that weaning weight cannot be satisfactorily adjusted for these environmental factors by the use of standard corrections. The correlations between estimated effects from the three methods were significant, and correlations between the three adjusted weaning weights exceeded 0.9 in most cases. All three methods accounted for similar fractions of variance in weaning weight, but average daily gain correction actually increased the variance on some occasions. Since least squares estimation is complicated, it is concluded that the pooled regression method is better suited to performance recording applications, especially if corrections are estimated within weaning groups, as they should be in view of their variability.