Estimação de parâmetros genéticos para características de importância econômica em animais da raça Brahman

Abstract

The Brazilian beef cattle breeders are constantly using genetic improvement tools to obtain better results in the field. In this sense, studies with a wide variety of traits aim to identify animals with rapid development, adequate fat finishing, and precocious reproductive performance. Thus, our objectives were to estimate genetic parameters for body weight, reproductive, and carcass quality traits; evaluate the genetic trends over the years; and the influence of inbreeding on the phenotypes of Brahman cattle. The traits studied were body weights at 120, 210, 365, and 450 days of age (P120, P210, P365, and P450); scrotal circumference at 365 and 450 days of age (PE365 and PE450), age at first calving (IPP), gestation length (PG), stayability (STAY), rib eye area (AOL), backfat thickness (EGS), and rumpfat thickness (EGP8). The least squares method was used to determine the significance of the fixed effects on the studied traits, which were concatenated into contemporary groups. Genetic parameters were estimated using frequentist and Bayesian analyses, under an animal model. For the study of genetic trends and inbreeding depression, linear regression was used and the t-statistic was considered at the 5% significance level. Heritability estimates for P120, P210, P365, P450, PE365, PE450, IPP, PG, STAY, AOL, EGS, and EGP8 ranged from 0.10±0.03 to 0.43±0.06, respectively. Estimates of maternal heritability for P120, P210, P365, P450, PE365, PE450, and PG ranged from 0.07±0.02 to 0.15±0.03. The proportion of the maternal permanent environment for P120 and P210 was equal to 0.11±0.02. Genetic correlations ranged between 0.60±0.25 (between STAY and EGS) and 0.97±0.01 (between P365 and P450). Except for IPP, all genetic trends were significant (p < 0.05) and favorable. There was a significant effect (p < 0.05) of inbreeding for P120, P210, P365, P450, and IPP, which were adjusted to their respective fixed effects. Based on the evaluated genetic trends, it was possible to verify that the selection conducted for most of the studied traits has been efficient and resulted in favorable annual genetic gains. Greater attention to the mating systems is indicated to control inbreeding in the population of Brahman cattle. Reproductive traits of high economic importance, difficult to measure, and with low heritability, such as IPP and STAY, can be helped with the selection in PE365, taking into account its moderate heritability and favorable genetic correlations with these traits. The emphasis applied to the selection of body weight traits, especially for P210, may help AOL. Although not included in the breed selection index, EGS and EGP8 present genetic variability and could respond to selection.