Growth curve and genetic parameters for carcass traits in cattle

Abstract

The aims of this study were to evaluate the adjustment of nonlinear models to longitudinal and transversal methods live weight data of Angus males in order to select the best model. In addition, we also aimed to estimate the components of (co)variance, heritability and correlation of carcass traits and performance in Angus cattle. The experimental data were obtained from Santa Éster farm of Casa BrancaAgropastoril Ltda. The models were compared following goodness-of-fit criteria: coefficient of determination (R²), residual standard deviation (RSD) and Akaike information criterion (AIC). The model parameters were estimated by the least squares method, based on the R software routine. The covariance components were estimated by Restricted Maximum Likelihood methodology using an animal model with fixed effects and random additive and direct genetic effects with the AIREML program. In Chapter I, the adult weight estimated by the models ranged from 588 kg to 627 kg. Antagonistic behavior was observed between the adult weight and precocity index parameters. There was a greater intensity of growth up to approximately five months of age and from 36 months of age on it was observed that the growth curve tends to stabilize. The goodness-of-fit criteria indicated that Von Bertalanffy was the most suitable model to describe growth curve of Angus cattle. In Chapter II, adult weights estimated by the longitudinal and transversal methods were 461 kg and 627 kg, respectively. It was observed that the growth pattern in the longitudinal methodology was intense and continuous up to 21 months of age. The transversal methodology showed a better adjustment of asymptotic weight and maturity index to the data set studied and the growth pattern had a sigmoid formation. Thus, it was stated that the transversal method of data collection can be applied in the study of growth curves in cattle, reducing the time needed for the construction of animal’s growth curve. In Chapter III, the heritability (h2) estimated for the characteristic rump fat thickness (RFT) was of low magnitude (0.18). For the characteristics of weight, subcutaneous fat thickness (SFT) and percentage of intramuscular fat (IMF), h2 were moderate (0.36, 0.22 and 0.36, respectively) and h2 for rib eye area (REA) was of high magnitude (0.41). Estimates of genetic correlations between weight and REA (0.91), weight and SFT (0.83), weight and RFT (0.77), REA and RFT (0.78) and between SFT and RFT (0.99) were positive and of high magnitude. The correlation between weight and IMF was high and negative (-0.85). Correlations of moderate magnitude were estimated between REA and SFT (0.50) and REA and IMF (-0.59). The correlation between SFT and IMF (0.23) was low magnitude. The results indicate that selecting for weight we can obtain a response to selection in the carcass characteristics, except for IMF.