VARIANCE COMPONENT AND HERITABILITY ESTIMATES OF EARLY GROWTH TRAITS IN THE ELSENBURG DORMER SHEEP STUD

A total of 8 909 birth weight and 7 740 weaning weight records, from t he progeny of 215 sires, collected from 1943 to 1990 from the Elsenbur g Dormer sheep stud, were analysed. Additive genetic variance and heri tability estimates for birth weight (BW), weaning weight (WW), average daily gain (ADG) and the Kleiber ratio (KL) were obtained by Restrict ed Maximum Likelihood (REML) procedures fitting three different models . Estimates were severely biased upwards when an animal model, ignorin g maternal effects, was fitted. A sire model yielded more realistic es timates of direct additive variance. Estimates of maternal genetic var iance and corresponding heritabilities (h2m) were higher than estimate s for direct additive variance and heritability (h2a) when fitted simu ltaneously in an animal model. The genetic correlations between direct and maternal influence were consistently negative but the proportion of cov (a, m) to phenotypic variance decreased from birth to weaning. The heritability estimates were as follows: BW = 0.12, 0.42, 0.16, 0.4 3; WW = 0.12, 0.34, 0.13, 0.20; ADG = 0.13, 0.31, 0.13, 0.18; KL = 0.1 3, 0.26, 0.14, 0.14 for a sire model, animal model, animal model direc t effects (h2a) and animal model maternal effects (h2m), respectively.