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 Breeders Association was analysed. From a data set of 64,962 animals, which had either birth (BW), weaning (WW), yearling (YW), or final weight (FW) records a subset of 17 herds comprising 18,083 animals was used to obtain uni- and bivariate estimates of variance components. This subset had to be subdivided into six further subsets, called group herds. The models used allowed for additive genetic, maternal genetic, and permanent environmental effects and for a covariance between additive direct and maternal genetic effects. Estimates were pooled across group herds. The results for BW, WW, YW, FW were .33,.35, .37, and .30, respectively, for heritabilities and .074, .18, and .11 for maternal heritabilities (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 due to the problems associated with the estimation of r(AM).