MATERNAL EFFECTS FOR GROWTH TRAITS IN BEEF-CATTLE

Estimates of direct and maternal heritabilities, the genetic correlation between direct and maternal additive effects, and the permanent environmental variance as a percentage of the phenotypic variance (c2) were reported for weights of beef cattle at birth, weaning, yearling and 18 months. The data consisted of one Hereford and two Angus weight selection herds, analysed separately, recorded from 1969 to 1987 with a grand total of 7291 records. A univariate animal model was used. Direct and maternal heritabilities averaged 0.30 and 0.07 respectively for birth weight, 0.14 and 0.13 for weaning weight, 0.29 and 0.04 for yearling weight, and 0.32 and 0.04 for 18-month weight, whilst c2 terms averaged 0.05, 0.15, 0.03 and 0.01 respectively. Genetic correlations between direct and maternal genetic effects in the Angus data averaged 0.20, 0.03, 0.09 and 0.27, respectively. Genetic correlations in the Hereford data were 0.37, -0.35, 0.97 and 0.95, respectively. Animal models which ignored maternal effects tended to overestimate direct heritability.