Modelos para avaliação genética do peso à desmama de bovinos cruzados Charolês-Zebu

• Ano de defesa: 2007
• Autor(a) principal: Toral, Fábio Luiz Buranelo
• Orientador(a): Lopes, Paulo Sávio
• Banca de defesa: Martins, Elias Nunes , Alencar, Mauricio Mello de , Euclydes, Ricardo Frederico
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Avalição multirracial; Diferenças genéticas; Interferência bayesiana
• Palavras-chave em Inglês: Multiple-breed evaluation; Genetic variances; Bayesian interference
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS
• Link de acesso: http://locus.ufv.br/handle/123456789/1900

Both selection and crossbreeding are the available tools to promoting the genetic improvement of the livestock. When used in association, they can promote the productive indexes in cattle raising. Thus, there is a need for the development of alternatives for selection in crossbred population. So, weaning weight (W225) data relative to 56,965 Charolais-Zebu crossbred calves were used to the evaluation and development of statistical models for multiple-breed genetic evaluation. In the first study, some alternatives for modeling the effect of the age of dam at calving (AOD) and its interaction with the dam´ genetic composition upon W225 were evaluated. Continuous functions were more appropriate to modeling the AOD effect upon W225 than the AOD classes. A linear + quadratic - quadratic - quadratic segmented polynomial with knots at 6.33 and 10.66 years old was appropriately adjusted to the data, especially to the most extreme AOD. The AOD effects upon W225 of the crossbred dam´ calves can be obtained, by considering the curves obtained for both purebred Charolais and Zebu dams, based on the percent alleles descending from Charolais breed of the dam. In the second study, the alternatives for modeling the genetic and environmental effects influencing W225 were evaluated. The included interaction among the genetic and contemporary groups promoted significant improvement in the adjustment of the models. All breed and heterotic, individual and maternal effects are also important variation sources that should be taken into account in the multiple-breed genetic evaluation of the populations. The use of the multiple regression analysis to modeling the breed and heterotic, individual and maternal effects turned possible a better estimate of those effects for genetic groups with few records. In the third study, some situations were analyzed under different presuppositions on the genetic and residual variances. The animal model with heterogeneous residual and genetic variances showed better adjustment to the available data. The genetic variances for crossbred animals may be obtained from the linear function of the genetic variances of each involved breed and the variance due to segregation between breeds. The heterogeneity sources of the residual variances were the breed and heterotic, individual and maternal effects, the AOD, and the calf´s sex in association. If inadequate statistical models together with unappropriated presuppositions are adopted, it probably will reduce the genetic progress along the selected generations as a function of the mistaken identification of the genetic values of parents.