Prediction of genetic values of sires for growth traits of crossbred cattle using a multivariate animal model with heterogeneous variances.

The purpose of this study was to evaluate the effect of adjusting for heterogeneous variances across breed groups on prediction of breeding values (PBV) of selected sires and on breed of sire effects. Data on weights at birth (BWT), 200 d (WW), and 365 d (YW) of purebred and crossbred calves from matings of Angus (A), Hereford (H), Polled Hereford, Charolais, Shorthorn, Simmental, Limousin, Maine-Anjou, Chianina, Gelbvieh, Tarentaise, and Salers Bulls to A and H cows were used. Calf performance in H and A dams was treated as a different trait. Models compared included fixed birth year, cow age, and sex classes and crossbreeding effect as a covariate; random direct and maternal genetic and permanent environmental effects were also included, but their variance structure was different. Model I assumed homogeneous variances across breed groups. Model II accounted for heterogeneous variances. Sires were ranked based on PBV from each model, and means of PBV of selected sires were calculated based on Model II. Differences between mean PBV were small for BWT, intermediate for WW, and larger for YW. Differences in PBV of selected sires increased as selection intensity increased, but only for WW and YW. Large differences in mean PBV of selected sires between maternal environments (H vs A) were observed for WW and YW for various sire breeds. Means of PBV of selected sires based on Model II exceeded those based on Model I by 6 to 16 kg of YW for various selection intensities and maternal environments. Estimates of breed of sire effects from Model I or II were similar for BWT and WW, but large differences were found for YW. Results indicate that some additional economic returns may be gained by commercial producers if sires are chosen across breeds based on predicted genetic values computed with models accounting for heterogeneous variances.