ABSTRACT
ABSTRACT: The present study aimed to estimate adaptability and stability parameters for Nellore bulls in 3 different regions. The traits analyzed included the weight of the animals raised in pasture at 420 days of age (W420) and at the age at first calving (AFC). The information used in this study was related to the phenotypic mean of the females which were the offspring of the top ten classified bulls based in one region. We used the methods proposed by Finlay & Wilkinson (1963) & Eberhart and Russell (1966) in order to evaluate the parameters of adaptability and stability of these animals. The averages estimated by the method of least squares were 243.91±34.90 kg and 1182.54±57.82 days, respectively, for the traits W420 and AFC. Adaptability and stability parameters for the W420 characteristic showed that it is feasible to identify bulls with predictable behavior in different environments, and that these animals may generate progenies which may achieve above-average performance. Behavior of the 10 bulls analyzed in the different regions studied for the traits W420 and AFC showed that the herds and the regions influenced the performance of their progenies. The methods used allowed us to identify bulls with general adaptability, high stability, and better performances, which may be the most suitable to be used in herds in which the genetic merit of the cows and the environment where the progenies will be raised are both unknown.
RESUMO: O objetivo deste trabalho foi estimar parâmetros de adaptabilidade e estabilidade para touros da raça Nelore em três regiões diferentes. As características analisadas foram o peso aos 420 dias de idade (P420) e a idade ao primeiro parto (IPP) de animais criados em regime de pasto. As informações utilizadas no estudo foram referentes a média fenotípica das fêmeas, filhas dos dez melhores touros classificados com base em uma região. Para avaliar os parâmetros de adaptabilidade e a estabilidade foram utilizadas as metodologias propostas por FINLAY & WILKINSON (1963) e EBERHART & RUSSELL (1966). As médias estimadas pelos métodos dos quadrados mínimos foram de 243,91±34,90kg e 1182,54±157,82 dias, respectivamente, para as características P420 e IPP. Os parâmetros de adaptabilidade e estabilidade para a característica P420 mostraram que é possível identificar os touros com comportamento previsível nos diferentes ambientes e que poderão gerar progênies com desempenho acima da média. O comportamento dos dez touros analisados nas diferentes regiões estudadas para as características P420 e IPP, evidenciaram que os rebanhos e as regiões influenciaram na performance de suas progênies. Por meio das metodologias aplicadas é possível identificar touros com adaptabilidade geral, alta estabilidade e com melhores desempenhos, os quais seriam os mais adequados a se utilizar em rebanhos em que não se conhece o mérito genético das vacas e nem o ambiente onde serão criadas as progênies.
ABSTRACT
The aim of this investigation was to study the influence of maternal effects on the genetic evaluation of sire production in Tabapuã beef cattle. Single and multiple trait analyses were done with adjusted animal weights at 120, 240 and 420 days of age. Antagonism was observed between additive direct and maternal genetic effects, with the maternal effect being higher until weaning. The inclusion of maternal effects in the models removed part of the additive variance only in single trait analyses and resulted in smaller means and standard deviations for the sire breeding values. The use of maternal effect associated with single or multiple traits may affect sire ranking. The contradictory results of the single and multiple trait analyses for additive direct and maternal effects indicate that caution is needed when considering recommendations about the importance of maternal effects in Tabapuã beef cattle.