Modelagem da produção de leite de cabras das raças Alpina e Saanen utilizando regressão aleatória

• Autor(a) principal: Brito, Luiz Fernando
• Data de Publicação: 2012
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4769
• topic: Funções de Covariância; Heterogeneidade residual; Legendre; Splines; Legendre; Splines; Covariance functions; Heterogeneity residual; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS

A total of 17,356 test-day records from 642 first lactations of Alpine goats and 13,278 records of 470 Saanen goats from the herd of Universidade Federal de Viçosa were used in this study. The objective was to model variations in test-day milk yield during the first lactation of Alpine and Saanen goats by random regression model (RRM), using orthogonal Legendre polynomials and B-splines in order to obtain adequate and parsimonious models for the estimation of genetic parameters. The analyses were performed using a single-trait RRM, including the direct additive, permanent environmental and residual random effects. In addition, contemporary group, type of kidding, genetic grouping, kidding order and linear and quadratic effects of the age of goat at calving were included as fixed effects. The mean trend of milk yield, and the additive genetic and permanent environmental covariance functions were estimated by random regression using different orders of orthogonal Legendre polynomial (3 to 6) and on B-spline functions (linear, quadratic and cubic, with 3 to 6 knots) and was evaluated different number of classes of residual variances. The criteria for selection of the models were the logarithm of restricted maximum likelihood function, Akaike information criterion, Bayesian information criterion and the Likelihood Ratio Test (LRT). The covariance components and the genetic parameters were estimated by the restricted maximum likelihood method. The program WOMBAT was used in all genetic analysis. Heritability estimates presented similar trends for the both functions and the estimates were different for Alpine and Saanen breeds. RRM s with a higher number of parameters were more useful to describe the genetic variation of test-day milk yield throughout the lactation. The most suitable RRM for genetic evaluation of PLDC of Alpine goat breed is a quadratic B-spline function, with six knots, to the mean trend and curves of additive genetic effects, permanent environmental effects and five classes of residual variance. The most recommendable RRM for genetic evaluation of PLDC Saanen goat breed is a cubic B-spline function, with six knots, to all curves and five classes of residual variances.