ESTIMATION OF DIRECT AND MATERNAL (CO)VARIANCE COMPONENTS FOR GROWTH TRAITS IN AUSTRALIAN SIMMENTAL BEEF-CATTLE

Field data on weight recordings provided by the Australian Simmental B reeders Association was analysed. From a data set of 64,962 animals, w hich had either birth (BW), weaning (WW), yearling (YW), or final weig ht (FW) records a subset of 17 herds comprising 18,083 animals was use d to obtain uni- and bivariate estimates of variance components. This subset had to be subdivided into six further subsets, called group her ds. The models used allowed for additive genetic, maternal genetic, an d permanent environmental effects and for a covariance between additiv e direct and maternal genetic effects. Estimates were pooled across gr oup herds. The results for BW, WW, YW, FW were .33,.35, .37, and .30, respectively, for heritabilities and .074, .18, and .11 for maternal h eritabilities (not estimated for FW). Significant correlations between direct and maternal genetic effects (r(AM)) existed for WW and YW in the magnitude of -.39 and -.22. However, further research is needed du e to the problems associated with the estimation of r(AM).