RESUMEN
The objective was to estimate the growth curves and genetic parameters using random regression methodology for Nellore cattle raised in Pantanal, MS, Brazil (6974 calves; n = 53,233 weights), with at least four weighings per individual. The model considered direct and maternal genetic additives and maternal permanent environmental effects at random. Orthogonal Legendre polynomials of cubic order were used to fit the growth curve. Analyses of variance were performed using the GLM procedure. The model used contained the fixed effects of sex, year of birth, farm, and the covariates calf birth month (linear and quadratic) and cow age at calving (linear and quadratic). The adjusted mean weight at 120 days of age was 93.43 ± 19.78 kg, and for 205 days of age, it was 180.42 ± 26.58 kg. Animals born in the dry season had a higher average weight [kg] (219.57 vs. 211.78, 3.7% higher) and, consequently, had higher weights at 646 days of age. Estimates of direct heritabilities (h2a) ranged from 0.35 to 0.75 (high magnitudes), and maternal heritabilities (h2m) along the trajectory of low magnitudes ranged from 0.03 to 0.08, respectively. The use of random regression to evaluate beef animals allows for adjusting the growth curve and selecting the best animals to be the parents of future generations.
RESUMEN
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.
RESUMEN
The objective of this study was to characterize Nelore cattle on central performance tests in pasture, ranked by the visual classification method EPMURAS (structure, precocity, muscle, navel, breed, posture, and sexual characteristics), and to estimate genetic and phenotypic correlations between these parameters, including visual as well as production traits (initial and final weight on test, weight gain, and weight corrected for 550 days). The information used in the study was obtained on 21,032 Nelore bulls which were participants in the central performance test at pasture of the Brazilian Association for Zebu Breeders (ABCZ). Heritabilities obtained were from 0.19 to 0.50. Phenotypic correlations were positive from 0.70 to 0.97 between the weight traits, from 0.65 to 0.74 between visual characteristics, and from 0.29 to 0.47 between visual characteristics and weight traits. The genetic correlations were positive ranging from 0.80 to 0.98 between the characteristics of structure, precocity and musculature, from 0.13 to 0.64 between the growth characteristics, and from 0.41 to 0.97 between visual scores and weight gains. Heritability and genetic correlations indicate that the use of visual scores, along with the selection for growth characteristics, can bring positive results in selection of beef cattle for rearing on pasture.