Nonlinear models to describe the growth curves of testicular and morphometric traits of Mangalarga Marchador stallions

• Ano de defesa: 2020
• Autor(a) principal: Silva, Danielle Estanislau Coelho
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Manga-larga (Cavalo); Testículos - Crescimento; Morfometria; Modelos não-lineares (Estatística); Reprodução Animal
• Link de acesso: https://locus.ufv.br//handle/123456789/28569

This study aimed to describe the testicular growth curve of testicular biometrics and body morphometry in Mangalarga Marchador stallions. Nonlinear models were fitted to total scrotal width (TSW), testicular volume (TV), body weight (BW) and withers height (WH). A cross- sectional study was conducted with 120 stallions, aging from 638 to 8006 days. The parameters of nonlinear models (Brody, Gompertz, Hill, Logistic I and II, Meloun I and II, Michaelis- Menten, Mitscherlich and von-Bertalanffy) were estimated by the Gauss-Newton iterative process. The goodness of fit was evaluated by the corrected Akaike’s (AICc) and Bayesian (BIC) information criteria, Adjusted R 2 , error sum of square (ESS), mean absolute deviation (MAD) and average prediction error (APE). Based on the goodness of fit, the Logistic I model fitted better to the growth curve of TSW, BW and WH; while Logistic II fitted better for the TV growth curve. Despite the high and positive correlation between TSW and TV (r = 0.85), the evaluation of testicular development by only TSW does not fully describe the stages of development of the testes, since TSW does not consider the growth of other biometric measures, especially the testicular height that maintains growth for a longer period. Therefore, to determine the testicular development phase, in which the stallion is found, by biometric evaluation, the best option is to evaluate all testicular measurements and thus obtain the TV as well. In addition, the moderate and positive correlations between WH with TSW and TV (r = 0.51 for both) indicate that biometric and morphometric characteristics are associated, so testicular biometry can be included in the genetic selection programs of Mangalarga Marchador stallions. Keywords: Mangalarga Marchador. Horses. Testicular biometrics. Body morphometry. Nonlinear models. Growth curves.