Avaliação do desempenho na pré e pós-desmama para diferentes grupos genéticos em uma população multirracial Aberdeen Angus-Nelore.

Abstract

The objective of this study was to evaluate the breed additive genetic and heterozygotic effects, direct and maternal, on the weight and the average daily gain for a multibreed population Aberdeen Angus-Nellore. They were studied the characteristics adjusted weight to 205 days of age (P205) and to 550 days of age (P550) and average daily gain from birth to weaning (GMD_ND) and from weaning to 550 days of age (GMD_DS). The data was furnished by Gensys Consultores Associados S/C Ltda. and Natura Genética Sul Americana, and it contained records on 121,241 animals sired by 1,359 bulls and 84,465 cows, raised in 104 farms in differents brazilians states from 1986 to 2002. The data was analyzed by two different methodologies: Genetic Group Model (MGG) and Multiple Regression Method (MRM). In paper number one, pre-weaning period, it were used records on 96,502 animals, sired by 962 bulls and 67,231 cows, grouped in 2,542 contemporaneous groups (GC) and 45 genetic groups (GG). The model used for the analysis by MGG, included as fixed, the effects of contemporaneous group-GC (including the animals born at the same farm, year and season and belonging to the same sex and management group), genetic group-GG (genetic additive effect of the animal individual breed, paternal and maternal), and the covariables age of the animal at weaning (IDD) and age of the cow at parturition (IVP), as linear and quadratic effects. For the MRM analysis, the data was firstly adjusted for the effects of GC, and for the covariables IDD and IVP, linear and quadratic. After that, it was performed a MRM considering the direct and maternal additive genetic effect of the breed and the direct and maternal heterozigosity. In the paper number two, post-weaning period, it were evaluated performances of 40,310 animals, sired by 720 bulls and 31,136 cows, distributed in 650 contemporaneous groups and 33 genetic groups. The model adopted by MGG considered as fixed, the effects of contemporaneous group (including the animals born at the same farm, year and season and belonging to the same sex and management group at 550 days of age) and the covariables IVP, linear and quadratic effects and the age of the animal to the age standard of 550 days was done (ISA), as linear effect. The MRM analysis was performed at the same way that for paper one. For the pre-weaning period, the results of this work alloud us to conclude that the direct additive genetic effects from Aberdeen Angus breed in relation to Nellore breed give better performances; the direct and maternal heterozygosity effect were high and significant, suggesting that crossed calves and cows can perform better than the pure breeds. For the pre-weaning period the estimatives obtained by MRM were similar to those obtained by MGG. In relation to the post-weaning period it were observed differences in the performances of the animals, showing a better efficiency of Aberdeen Angus breed additive genes in relation to the Nellore breed. By the regression coefficient for direct and maternal effects it is possible to conclude that exist a bigger influence of the direct in relation to the maternal effect, suggesting that, in this phase, the animal performance depends most of its breed composition than of the influence of it mother. In spite of to exist similarities among the estimatives obtained by MGG and MRM, it is not recommended the use of MRM because of the inconsistencies observed in the results by this method.