A. Gondo

Interação genótipo x ambiente em características de crescimento de bovinos da raça Nelore no Mato Grosso do Sul

The effect of genotype x environment interaction on body weight at birth (BW), weaning (W205), 12 (W365) and 18 (W550) months of age of Nellore cattle raised in the regions of Alto Taquari, Campo Grande and Pantanal, MS, Brazil, was studied. The data were analyzed for each region separately and for all regions together. Variance and covariance components and genetic parameters were estimated by the restricted maximum likelihood method, using an animal model that included the random additive direct effect, and the fixed effects of sex and contemporary group (herd, year, season and region of birth), and sires were ranked based on their breeding values (BV). The results showed that the additive direct and residual variances were different among regions. The heritability estimates ranged from 0.16 to 0.66 (BW), 0.36 to 0.59 (W205), 0.35 to 0.49 (W365) and 0.30 to 0.45 (W550), depending on the region. Pearsons correlation coefficients between BVs of sires, obtained for each pair of regions, showed means equal to 0.11 (BW), 0.38 (W205), 0.38 (W365) and 0.39 (W550). When the correlations were for the BVs obtained for each region with the BVs obtained for all regions together, the estimates were higher showing means equal to 0.80 (BW), 0.88 (W205), 0.88 (W365) and 0.87 (W550). Despite the high values of these last ones, the results show evidence of genotype x environment interaction, and that regional genetic evaluations, when available, can be more useful than a state evaluation.

Estimation of genetic parameters for growth traits in Tabapuã cattle using a multi-trait model

To provide information that can contribute to the genetic evaluation and selection in Tabapua cattle, genetic parameters were estimated for growth traits using a multi-trait animal model. (Co)variance components were estimated by a Bayesian approach using the Gibbs Sampler. Moderate and similar responses to selection are expected when selecting for weights at the four ages evaluated, since the direct heritability estimates were similar and of average magnitude (0.18 to 0.19). The direct and maternal additive genetic correlations between all pairs of weights were higher than 0.70, indicating a high degree of association between the four traits. This suggests that using any of them as selection criteria will result in correlated response in the others and that multi-trait analysis are recommended for the genetic evaluation of growth traits in beef cattle for exploiting this association.