Estimation and interpretation of direct and maternal genetic parameters for weights of Australian Angus cattle

REML estimates of genetic parameters in field data from Australian Angus cattle were similar to estimates for other British breeds in Australia. The main difference was a smaller permanent environmental effect of dam than in breeds such as the Hereford. Heritabilities of birth, weaning, yearling and 600 day weight were estimated to be 0.35, 0.20; 0.24 and 0.25, respectively, for direct effects and 0.08, 0.09, 0.06 and 0.04 for maternal effects. Dam environmental effects were 0.05, 0.14, 0.07 and 0.04 and phenotypic variances 14, 501, 754 and 1152 kg(2). Correlations between birth and later weights were 0.52-0.59 (direct genetic), 0.45-0.76 (maternal genetic), 0.37-0.54 (maternal environmental) and 0.12-0.19 (residual). Correlations among post birth weights were 0.84-0.90 (direct genetic), 0.86-0.87 (maternal genetic), 0.84-0.94 (maternal environmental) and 0.49-0.62 (residual). When fitted, estimates of the correlations between direct and maternal genetic effects were large and negative. Examination of the correlations between estimated breeding values and the fitting of alternative models suggested, however, that such correlations were a consequence of other effects in the data, rather than evidence of a true negative genetic relationship.