Avaliação do desempenho na pré e pós desmama para uma população bovina multirracial Aberdeen Angus x Nelore utilizando diferentes modelos genéticos

Abstract

The objective of this study was to estimate the genetic effects that affect the pre and post weaning performances of animals, products from Aberdeen Angus (A) and Nellore (N) breeds crosses. In Article 1, there were used the weaning weights (PD) to test five genetic models (M). The M1, complete, containing the fix breed genetic effects direct additive (AD) and maternal (AM), the heterozygote effects direct (HD) and maternal (HM), the epystatic effects direct (HD) and maternal (HM) and joint additive effects direct (ACD) and maternal (ACM); M2, was equal to M1, excluding ACD and ACM effects; M3, was equal to M1, excluding ED and EM effects; M4, was equal M1, excluding ED, EM, ACD and ACM effects, and M5, was equal M1, excluding HD, HM, ED, EM, ACD and ACM effects. The models were submitted to three different analysis methods: Least Square Means method (MQM), Ridge Regression Method (RC) and Restricted Maximum Likelihood Method (REML). The different tests used to check the methodologies efficiency and to compare the models allowed to conclude, for this population, that: the dominant additive models usually used for genetic evaluations, do not give a good description of the pre weaning variations, being necessary to add the heterozygote and epystatic effects; the joint additive effects do not improve substantially the adjustment of the analysis model and the heterozygote effects were efficient to represent a quadratic breed additive effect, beyond of to insert a bias related to the joint additive effects co linearity. In Article 2, there were used the weight at yearling (PS) to test five genetic models as previously described, only excluding the maternal effects. The models were submitted to three different analysis methods: MQM, RC and REML. The RC method estimate coefficients with magnitude and sign with biological explanations. The estimative obtained were different from one to the other model, indicating the importance of to choose the adequate model to perform one analysis. It is necessary to decide based on a previous knowledge of the studied phenomenon, it biological interpretation, and the relationship between the independent variables. It was important to include the effects caused by heterozygosis and epystasis in the model besides the additive effect. The mathematic notation nowadays used for the joint additive effects, and tested in this study, were not able to explain the between breed complementarily, as was expected, because of the multi co linearity between the effects studied.