Variabilidade Genética do Peso Adulto de Matrizes em um Rebanho Nelore do Estado de São Paulo

Abstract

Records of 776 Nellore cows from a herd raised at São Paulo State, Brazil, were analyzed to determine the cow mature weight and to estimate their genetic and phenotypic parameters. A previous analysis showed that month and season of birth were not important sources of variation for the cow mature weight. This trait was influenced most by the month when the cows were weighted (April or July) and by the age of the cow (4 to 14 years, at the midpoints of the intervals). It was then used a linear mixed model that included the fixed effects of age of the cow and month of the weighing, combined in 22 classes, and the animal genetic additive effects. The average cow mature weight was 458 kg, varying from 330 through 585 kg, with a standard deviation of 39 kg and cows were in average 7.6 years old. The phenotypic, genetic and environmental variances were 1,544,561, and 983 kg 2, respectively, resulting on a heritability estimate of 0.36. The predicted genetic values for cow mature weight ranked from - 40.1 kg through +44.4 kg, showing that success may be attained by including this new trait as an alternative selection criteria for the Brazilian Nellore genetic improvement programs.