Curva de crescimento em altura na cernelha de equinos da raça Mangalarga Marchador considerando-se heterocedasticidade

Abstract

RESUMO Objetivou-se, com este estudo, avaliar o ajuste dos modelos de Brody, Gompertz, Logístico e Von Bertalanffy aos dados de altura na cernelha de equinos Mangalarga Marchador, ponderando pelo inverso da variância, a fim de selecionar o melhor modelo e predizer sobre o crescimento e a maturidade dos animais dessa raça. Foram utilizados dados de 230 equinos dos seis aos 176 meses de idade, os quais foram divididos por sexo e em 16 classes de idade. Os modelos estudados foram comparados segundo os avaliadores de qualidade: coeficiente de determinação (R2); desvio padrão residual (DPR) e critério de informação de Akaike (AIC). A estimação dos parâmetros dos modelos foi realizada pelo método de mínimos quadrados ponderado no software R. Todos os modelos avaliados se mostraram adequados para descrever a curva de crescimento em ambos os sexos. Perante os avaliadores utilizados, o modelo Logístico foi o mais adequado para descrever as curvas de crescimento em altura na cernelha nos dois sexos da raça Mangalarga Marchador. Observou-se também um crescimento acelerado nos primeiros meses de idade. Os animais machos atingiram uma altura adulta maior, porém as fêmeas são mais precoces, pois apresentaram maior estimativa para o índice de maturidade.

Growth curve for height at withers and body length of Mangalarga Marchador horses

“…This also confirmed the efficiency of the cross-sectional data collection methodology for obtaining growth curves. RIBEIRO et al (2018) reported for height at withers in MM animals, with approximately 147 cm for females and 149 cm for males, using the logistic model. SOUZA et al 2019also reportedsimilar values for height at withers and body length, for adult females (146.4-148.3 cm and 148.5-151.6, respectively) and for males (148.5-151.8 and 150.7-154.8, respectively).…”

“…The Research Ethics Committee of the Federal University of Lavras approved the study under protocol 039/12. Two hundred thirty Mangalarga Marchador (MM) animals were used (96 males and 134 nonpregnant females), 6 to 176 months of age, which were divided into 16 age classes and by sex, as described in RIBEIRO et al (2018). Animals older than 36 months were officially registered as the Mangalarga Marchador breed.…”

“…An alternative is to use a cross-sectional method, where the variables can be collected once per individual. This methodology has been demonstrated to be effective in human (SPERANDIO et al, 2011) and equine (RIBEIRO et al, 2018;SOUZA et al, 2017;SOUZA et al, 2019) growth studies.…”

Morphometric characteristics of the Mangalarga Marchador horse breed determined by nonlinear models

“…Since the breed's inception less than 200 years ago, its biotype has become more athletic, with higher quality morpho-functional features for a saddle horse (Casiuch, 2016). In this context, several studies have evaluated the growth characteristics of the horses of this breed (Souza et al, 2017;Ribeiro et al, 2018); however, few of them take into account morphometric variables, such as body length and thoracic and cannon perimeters, in statistical modeling.…”

“…However, acquiring data on the Mangalarga Marchador breed is difficult because most horses are sold by their owners before their growth stops at approximately five years of age. The transversal method is a practical and inexpensive alternative that allows collecting variables in a single event, shown to be very efficient in evaluating human (Zeferino et al, 2003) and horse (Souza et al, 2017;Ribeiro et al, 2018) growth.…”