Curvas de crescimento em equinos da raça mangalarga marchador utilizando método transversal

Abstract

The Mangalarga Marchador (MM) breed is among the most numerous Brazilian breeds and widely distributed throughout the national territory. The study of animal growth curves based on nonlinear models has often been used as a method for the analysis of the development of various species, however, there is no report of a study on the modeling of the growth curve in this breed. The objective of this work was to evaluate the fit of the Brody, Gompertz, Logistic, Von Bertalanffy and Quadratic Response Plateau models to the cross-sectional data of the body weight (BW) (Chapter I) and morphometric measures (MMs) (Chapter II), in MM horses, in order to select the best model and predict growth and maturity of males and females of this breed. The experimental data were obtained at an agricultural exhibition in Belo Horizonte, Minas Gerais, Brazil, in the year 2012. BW data were obtained from 214 animals (94 males and 120 females) and MMs data of 200 animals (75 males and 125 females) of MM, aged between six and 153 months. These were weighed individually on conventional mechanical scales and measured in height at the withers (HW), body length (BL), thoracic perimeter (TP) and cannon (CP). The nonlinear models used were Brody, Gompertz, Logistic, Von Bertalanffy and Quadratic Response Plateau segmented model. The parameters of the model were estimated by employing the method of least squares, using the Gauss-Newton numerical algorithm based on R software routine. The normality of the data was verified by the Shapiro-Wilk test. The comparison and selection of the adequate model to describe the growth curve were performed using the Coefficient of determination (R²); Residual Standard Deviation (RSD); Akaike's Information Criterion (AIC). In Chapter I, the adult BW estimated by the models ranged from 431 kg to 439 kg for males and 416 kg for 420 kg for females. The Von Bertalanffy model was the most efficient for expressing the growth of BW in males and that of Brody for females. MM females are more precocious than males to reach adult BW. In Chapter II the adult HW estimated by the models ranged from 146.25 to 148.34 cm for females and from 148.55 to 151.80 cm for males. The adult BL ranged from 148.59 to 151.64 cm for females and from 150.77 to 154.88 cm for males. Adult TP ranged from 179.07 to 182.88 cm for females. The TP data of the males did not present normality. Adult CP ranged from 18.25 to 18.76 cm for females and 18.95 to 19.41 cm for males. The use of the logistic model to express the growth in HW, BL and CP of the males and the Brody model for HW, BL, TP and CP of females is more indicated. Females present greater precocity than males, except for CP. The cross-sectional data collection can be applied in the study of growth curves, in body weight and morphometric measures.