Arthur dos Santos Mascioli

Correlações genéticas entre características produtivas de fêmeas em um rebanho da raça Canchim

The objective of this study was to estimate the genetic correlations of female body weights at weaning (BWW), 12 (W12) and 18 (W18) months of age with age at first calving (AFC), body weight at first calving (WFC), adult body weight (ABW), and the parameters for mature weight (A) and maturation rate (k) obtained using the Von Bertalanffy model, in a Canchim herd. The restricted maximum likelihood method, with two-trait analyses, was used with models that included the fixed effects [...]The objective of this study was to estimate the genetic correlations of female body weights at weaning (BWW), 12 (W12) and 18 (W18) months of age with age at first calving (AFC), body weight at first calving (WFC), adult body weight (ABW), and the parameters for mature weight (A) and maturation rate (k) obtained using the Von Bertalanffy model, in a Canchim herd. The restricted maximum likelihood method, with two-trait analyses, was used with models that included the fixed effects of contemporary group and the random additive direct effect. For BWW the model also included the covariate age of cow at calving (linear and quadratic effects) and the additive maternal and the permanent environmental random effects, and for ABW the model included also the fixed effect of age of cow. The means of the heritability estimates were equal to: 0.37 (BWW), 0.31 (W12), 0.35 (W18), 0.39 (A), 0.29 (k), 0.13 (AFC), 0.39 (WFC), and 0.42 (ABW). The genetic correlations between BWW and the other traits were: 0.46 (A), 0.02 (k), -0.12 (AFC), 0.66 (WFC) and 0.42 (ABW). With W12 they were equal to 0.39 (A), 0.31 (k), -0.32 (AFC), 0.77 (WFC) and 0.66 (ABW), while with W18 they were equal to 0.21 (A), 0.42 (k), -0.29 (AFC), 0.65 (WFC) and 0.60 (ABW) These results indicate that selection to increase BWW, W12, W18, WFC, ABW, and parameters A and k should result in direct genetic responses, and that selection to increase female body weights from weaning to 18 months of age should result in favorable responses in AFC and parameter k, but in unfavorable correlated responses in WFC and ABW.

Evidências de interação genótipo x ambiente sobre características de crescimento em bovinos de corte

The objective of this study was to evaluate the genotype x environment interaction for body weight at weaning (WW) and 12 months of age (W12), average daily gain from weaning to 12 months of age (ADG), and performance based on a principal components index (PC) involving these three traits, in a Canchim (5/8 Charolais + 3/8 Zebu) herd. The environment was the season (semester) of birth, and two methods were used to evaluate the genotype x environment interaction: Method 1 - genetic parameters estimated by the derivative free maximum likelihood method (REML), using two-trait analyses (the same trait in the two seasons), and a model that included the effects of year and month of birth, sex and age of cow as a covariate (linear and quadratic effects), and the random effect of animal; and Method 2 - same methodology as Method 1, but with two statistical models, with or without the uncorrelated random effect of sire - season of birth, testing the difference between the two models using the likelyhood ratio test. By Method 1, the genetic correlations for the same trait in the two environments (seasons) were equal to 0.87, 0.97, 0.91 and 0.88 for WW, W12, ADG and PC, respectively. The heritability estimates were very similar for both environments, for all traits studied. By Method 2, the sire-season of birth effect was significant for all traits studied. These results show evidence of genotype x season of birth interaction for the traits studied, suggesting that, in this herd, genetic evaluation and selection should take this interaction into account.

Estudo da interação genótipo × ambiente sobre características de crescimento de bovinos de corte utilizando-se inferência bayesiana

The objective of this study was to evaluate the genotype × environment interaction for weaning and yearling weights, daily weight gain from weaning to 12 months of age and the growth performance in Canchim (5/8 Charolais + 3/8 Zebu) beef cattle estimated by a principal components analysis including those three traits. The environment was defined by season of birth (first and second semesters of the year). Genetic parameters were estimated by bayesian method with the Gibbs sampler using bivariate analyses (considering the trait in each of the two seasons as a different one) and models that included the fixed effects of year and month of birth, sex and age of cow (linear and quadratic) and the random effects of animal and residual. The results suggested that genetic evaluation and selection in Canchim beef cattle for the traits studied should consider the genotype and season of birth interaction.