Alternative Animal Models to Estimate Heritabilities and Genetic Correlations Between Direct and Maternal Effects of Pre and Post-Weaning Weights of Tabapuã Cattle

Abstract

The Tabapuã is a Zebu polled breed used for beef production, with white or gray hair coat and pigmented skin. Weaning (W205, 30,746 observations), twelve-month (W365, 27,701 observations) and 18-month (W550, 18,493 observations) body weights of Tabapuã cattle, raised on pastures in several regions of Brazil, from 1975 to 1995, were analyzed with four different single trait animal models (including or not the maternal genetic and/or the permanent environmental effects with the direct genetic effect). Genetic parameters and covariance components were estimated by restricted maximum likelihood method. For all three traits the most complete model that included all three random effects was the best. The model that included only direct genetic effects overestimated the additive genetic variance and heritability (0.27, 0.24 and 0.15 for W205, W365 and W550, respectively). When the permanent environmental effect was included in the model, the portion of the total variance due to it was 0.09, 0.06 and 0.02 for W205, W365 and W550, respectively, and the estimate of the additive genetic variance decreased. The inclusion of the additive maternal effect instead of the permanent environmental effect did not change the estimate of the additive direct variance. Heritability estimates, obtained with the most complete model, were low: 0.16, 0.17 and 0.13 for direct genetic effects, and 0.10, 0.03 and 0.03 for maternal genetic effects, for W205, W365 and W550, respectively. Estimates of genetic correlation between direct and maternal effects were negative, showing an antagonism between such effects. Maternal effects still remained evident after weaning, though they became less important.