Estimation of additive direct and maternal genetic and non additive effects and prediction of the performance of weights, scrotal circumference and muscling scores in a Bos taurus x Bos indicus, composite beef cattle population. / Estimação de efeitos genéticos aditivos diretos e maternos e não aditivos e, predição do desempenho de pesos, perímetro escrotal e musculosidade em uma população de bovinos de corte compostos (Bos taurus x Bos indicus)

Gerson Barreto Mourão

Data of weights at birth, weaning, 390 days, weight gain from weaning to 390 days, scrotal circumference and muscling scores at 390 days of age of a population used in the formation of the Montana Tropical® beef composite, raised under tropical conditions, were analyzed under three different models to: i) determine genetic and environment effects ii) determine the adjustment factors those effects; iii) study genetic contribution of additive direct and maternal breed effects and non additive genetic effects; iv) estimate genetic parameters and v) quantify the effects of those models on estimation of expected progeny differences. Three models studied were: Model RM - included the effect of group of contemporaries (GC), the class of age of the cow to the calving (CIMP), the covariates associated to the genetic additive maternal and direct breed effect and the covariates associated to the non additive genetic effect of heterozygosis; Model R considered the effects of model RM, except the maternal additive breed effect and Model H, that considered effects of model R, except the additive direct breed effect. The estimates of (co)variance components and genetic parameters were obtained by the REML methodology under an animal model. The GC effect was the main effect in the different characteristics. The effect of the CIMP was also very important and differences up to 30 kg were observed in weaning weights of young heifers (CIMP = 1) when compared to adult cows (CIMP = 4). Additive direct and maternal breed effects and heterozygosis, in a general, had been significant (P<0.05) for all the traits. Model RM seems to supply better estimates than models R and H, what it is confirmed in the process of prediction of the performance on the part of these models. The estimated genetics parameters were from average to the high magnitudes. It can be conclude that CIMP and GC effect must be incorporated in the modeling process. Models of estimation that are able to segregate and quantify the additive maternal and direct breeds effects and also the effect of heterozygosis, as model RM, must be elect. In general terms, model RM was able to predict the performance of the more frequent genetic combinations of this composite population. The variance components and heritability estimated can support selection programs. Biological type N contributed for the generation of cows that promote higher weaning and 390 days weights as compared to the biological types Adapted and British. In general the linear relation between heterozigoses and heterosis and must be considered in the genetic evaluations. The results evidence the genetic contribution of heterosis in the production systems and further and more complex models are needed to elucidate the composite populations (co)variance components estimation.

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