Growth curves of campolina horses using nonlinear models

Abstract

The Campolina horse breed stands out for its gait, its tall size, harmonious and curvaceous features, it is used in sports, leisure and service. The study of animal growth curves based on nonlinear models has often been used as a method for analyzing the development of several species, however, there are no reports of a study on modeling the growth curve in this breed. This present study aimed to evaluate the fit of the Logistical, Gompertz, von Bertalanffy and Brody models for the withers height (WH) and body weight (BW) in males and females, in addition to study the first to fourth order derivatives of the growth model aiming to identify relevant points of the growth curve. The experimental data were obtained from an agricultural show in Belo Horizonte, State of Minas Gerais, in 2012. A total of 356 Campolina horses were measured, 114 males and 242 non-pregnant females, which were divided into 16 age classes (7 to 203 months) and sex. Each animal was measured only once, characterizing a cross-sectional data collection study. The models were compared according to the following criteria for quality of fit: R2, AICc and MAPE. All adjustments and graphs constructed were analyzed by the statistical software R. The estimated asymptotic parameter for females in body weight were higher than those for males, indicating that they reach a higher adult weight, which may be due to different dietary practices, physiological conditions and physical conditioning between sexes. The maturity index of males was higher than for females, suggesting that the growth of males is more accelerated for withers height. The Gompertz model was chosen as the most suitable for the description of the growth curve in body weight and withers height of the Campolina breed horses because it presents best evaluators of quality and captures more influential points from its 1st to 4th order derivatives. Withers height develops faster than body weight. Some of the relevant points of equine growth still occur in the prenatal and lactation stages of foals.