Fitting of growth curves of Nellore cattle from Northern Brazil

Abstract

This study was carried out to determined the best nonlinear model to describe Nelore cattle growth. The models used (Brody, Von Bertalanffy, Gompertz and Logistic models) were fitted by Gauss-Newton method to weight-age data of birth to 750 days old of Nellore cattle raised in Northern Brazil. The models adjustment quality was made by mean square error, adjusted determination coefficient, prediction error, absolute mean deviation residuals, A and k biological parameters, graphics of observed and estimated weights, of instantaneous and relative growth rate and absolute maturity. The convergence criteria were satisfied for all nonlinear models. Estimative mean for A and k was 470.50kg and 0.002 dia-1; 357.80kg and 0.004 dia-1; 337.60kg and 0.005 dia-1; and 309.60kg and 0,008 dia-1 for Brody, Von Bertalanffy, Gompertz and Logistic nonlinear models, respectively. The data adjustment for weight-age of the animal provides information describing the growth curve and the future prognostic for animals managed under the same environmental situation. The properties of four nonlinear models were discussed concerning its applications in the fitting of growth curves in Nellore cattle production. In the period analyzed, Von Bertalanffy nonlinear model was indicated to estimate the body weight of Nellore cattle from Northern Brazil.