Avaliação genética de bovinos de corte compostos

• Autor(a) principal: Bueno, Rachel Santos
• Data de Publicação: 2007
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1271
• topic: Heterose; Bovino de corte; Compostos; Heterosis; Beef cattle; Composite; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::GENETICA E MELHORAMENTO DOS ANIMAIS DOMESTICOS

Genetic groups were used to estimate the heterosis and its profile along generations in the population of Tropical Montana composite. The genetic groups evaluated were: pure breed animals, F1, other crossbreds and Tropical Montana composites. It was used a pedigree data to calculate each animal generation. The data were adjusted for the effects of total maternal heterozygosis and heterosis. The heterosis estimation for each animal was obtained by the difference of the non-adjusted data and the adjusted for the non additives effects. The average heterosis for each generation was calculated, being the statistical significance of the contrasts of the mean verified by the hypothesis test. The estimations of the average heterosis in each generation were positive for all the evaluated traits. For W205 and SC390, the heterosis retention in the population was detected. The difference of profile of the tendency line of W390 is observed in the strong diminishing of the heterosis of F1 generation in comparison to the following generations, which can be an evidence of loss for genetic recombination. In the population the animals are grouped in biological types by racial composition in: N group, Bos indicus breeds; group A, adapted breeds; group B, British breeds, and group C, continental breeds. It was identified the racial composition of Montana sires in the population simulated the crosses with females ½ NxA, ½ NxB e ½ NxC and the resulted racial composition of the progeny. The aggregated value of the progeny was calculated from the additive and non additives genetic effects of the biological types estimated in the population, for an index and trait that compounds it. For the F1 females, the use of sires with high percentage of B, and moderate percentage of A are benefited, producing progenies with moderate to high magnitude heterosis coefficient. The procedure used was efficient and 65% of the superior sires would be selected, in any system of F1 female production, indicating high capacity of combination. Data were analyzed with the objective of evaluating the effect of the epistasis in the models of genetic evaluation. The analyzed traits were weight at 205 (W205) and 390 days (W390), and scrotal circumference at 390 days (SC390). The analyzes were made by the maximum likelihood method, considering two models: the model 1 which included as covariates the direct and maternal additive effects, and non additive of the heterozygosis for the direct and total maternal, and the model 2, which also considered the direct epistasis direct. The Akaike Information Criteria (AIC) and the Bayesiano of Schwartz Information Criteria (BIC) were used for the comparison of the models and the test of likelihood. The data were adjusted for the non additive effects estimated, and submitted to the analysis for the obtainment of the covariance and genetic parameters. The inclusion of the epistasis effects on the model did not alter much the estimation of the genetic additive (co)variances components and, consequently the heritability. However, it was significantly by the likelihood ratio test. By the AIC, the model 2 also gave better adherence to the data. Yet, by the BIC, the model 2 was more adequate, only for W205. The contribution of the non additive effects, when estimated by using the PROC GLM from SAS and by MTDFREML program, was investigated. It was also analyzed if the data must be pre-adjusted for the non additive effects or those effects can be included in the pattern of evaluation as covariates. The model that considers the epistasis was used, being the data adjusted for the non additive effects obtained. The genetic values of the steers (2004) and the sires classified in TA, with 300 or more measured sons; TM, with less than 300 and more than 39 sons, and TB with less than 40 sons, for the weight trait at 205 days were catalogued to verify alterations in the magnitude of predictions in relation with the two methods of correction for the non additive effects. Pearson and Spearman correlations among the genetic values for the weight at 205 days were superior than 0.94. The non additive effects can be included in the models as covariates.