Estimates of genetic parameters for weaning weight of beef cattle accounting for direct-maternal environmental covariances

Restricted Maximum Likelihood algorithm estimates of (co)variance components due to maternal effects as well as a regression on maternal phenotype were obtained for seven weaning weight data sets of Australian and New Zealand beef cattle. Fitting such regression, analyses accounted for environmental covariances between dams and their offspring. Results show a substantial, negative regression on maternal phenotype (up to -0.2) for Hereford field data, accompanied by small, negative estimates of a direct-maternal genetic covariance. In contrast, for Angus and Limousins, the direct-maternal genetic covariance was clearly more important than its environmental counterpart, i.e., for these breeds an estimate of the direct-maternal genetic correlation of about -0.5 could not be attributed to a negative environmental relationship which previously had not been modeled correctly. Fitting a sire x herd-year interaction as an additional random effect increased the likelihood dramatically for all data sets. While estimates of the regression on maternal phenotype were little affected, fitting the interaction reduced estimates of the direct-maternal genetic covariance, substantially so for Angus and Limousin, reducing (absolute value) estimates of the corresponding correlations to -0.3 to -0.2.