The objectivesof this study were to evaluate a multibreed heteroskedastic animal model (MAMR)to estimate residual variance heterogeneity due to breed, heterozigosity, sexand contemporary groups (CG) and robustness to outliers. Differences on variancecomponents, heritability and genetic values estimates were evaluated. It wasused 4,016 records of post weaning weight gain (PWG) from Brangus foundationherd of Embrapa Pecuária Sul. Data were analyzed by MAMR with four differentresidual distribution specifications, which were defined by the nature of residualvariance, homoskedastic (HO) or Heteroskedastic (HE) and by the Gaussian (G)or Student t marginal residual distribution. The best data fit was achivedby using MAMR-T-HE and it was observed heteroscedasticity due to sex and animalheterozigosity and among contemporary groups. There were substantial differencesin genetic variances of breed groups estimated by using different models andin the heteroskedastic, MAMR-G-HE and MAMR-T-HE. The greatest differences onheritability estimates occured among different breed groups. It was also noteda reordering in the ranking of superior animals regarded to genetic merit whenheterogenous residual variances and robustness to outliers were considered.Multibreed genetic evaluations by using the Student t distribution modelto describe residuals and assuming heterogenous residual variances are moreappropriate to perform inference on genetic merit of animals from crossbreedingprogenies of Angus and Nelore purebred animals.
