Avaliação genética do crescimento de bovinos da raça Simental utilizando modelos multicaracterísticos e de regressão aleatória

• Ano de defesa: 2012
• Autor(a) principal: Mota, Rodrigo Reis
• Orientador(a): Lopes, Paulo Sávio
• Banca de defesa: Toral, Fábio Luiz Buranelo , Resende, Marcos Deon Vilela de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Bovino de corte; Avaliação genética; Regressão aleatória; Crescimento; Peso corporal
• Palavras-chave em Inglês: Beef cattle; Genetic evaluation; Random regression; Growth; Bodyweight
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS
• Link de acesso: http://locus.ufv.br/handle/123456789/5725

Weight records from 10,659 Simmental beef cattle provided by the Associação Brasileira dos Criadores das Raças Simental e Simbrasil (Brazilian Association of Farmers of the Simmental and Simbrasil Breeds) (ABCRSS) were used to estimate the (co)variance components and genetic parameters for weights in the growth trajectory using multi-trait models (MTM) and random regression models (RRM). In the MTM analysis, the likelihood ratio test (LRT) was used to determine the significance of random effects included in the model and define the most appropriate model. All random effects evaluated were significant and included in the final model of analysis. In the RRM analysis, different adjustments of polynomials orders were compared for five different criteria to choose the best fit model. A model of third order for additive direct genetic, direct permanent environment, additive maternal genetic and maternal permanent environment effects was sufficient to model weight variances structure in the growth trajectory of the animals. The (co)variance components were in general similar in RRM and MTM. Direct heritabilities in MTM were slightly lower than RRM and they varied from 0.04 to 0.42 and 0.16 to 0.45, respectively. Additive direct correlations were mostly positive and high magnitude, being highest at closest ages. Considering the results and the facts that RRM can be implemented and the pre-adjustment of the weights to standard ages is not required, RRM can be recommended in genetic evaluation of Simmental beef cattle in Brazil. In a second study, weight records were used in genetic evaluation of growth by inclusion or exclusion of animals from the technique of embryo transfer (ET). One multi-trait model with exclusion of ET individuals (MTM1) contained 29,510 records of 10,659 animals and another one without exclusion (MTM2) contained 62,895 records of 23,160 animals. Records were adjusted for ages at 100, 205, 365, 450, 550 and 730 days old. Except the maternal permanent environment variance, (co)variance components were similar in both models. Direct heritabilities (h2d) in MTM1 were 0.04, 0.11, 0.20, 0.27, 0.31 and 0.42, and in MTM2 were 0.11, 0.11, 0.17, 0.21, 0,22 and 0.26, respectively, for ages at 100, 205, 365, 450, 550 and 730 days. The estimates of h2d for MTM1 were higher than MTM2 from the weight at 365 days. Additive direct genetic correlations in both models were moderate to high, indicating that the characteristics should be determined mostly by the same genes. The animals from the technique of embryo transfer can be included in genetic evaluation of Simmental beef cattle in Brazil, resulting in potential accuracy in genetic evaluations and genetic gains due the reduction of the generation interval. In a third study, random regression models (RRM1 and RRM2) were used on the same weights records from the second study to genetic evaluation of growth by inclusion or exclusion of ET animals. In general, the (co)variance components were similar in both models, except the maternal permanent environment and residual components. In RRM1, oscillation was observed at the beginning of the trajectory in maternal permanent environment component. The residual component in RRM1 was higher than RRM2, indicating potential higher accuracy in RRM2. The direct heritability in RRM1 and RRM2 presented similar behavior with oscillations in the curve and were slightly higher in RRM1, ranging around 0.1 to 0.5, and in RRM2 ranged between 0.1 and 0.4. The estimates of correlations were generally the same and smaller as the ages have distanced themselves. These results suggest that the inclusion of animals from the technique of embryo transfer in the process of genetic evaluation can be done using random regression models inasmuch the inclusion of these animals would provide greater genetic gains per unit time due the reduction of the generation interval by the use of this reproductive technique.