Genetic parameters of growth at different ages in zebu cattle

Abstract

In order to evaluate the duration of the behavior tests of zebu males in pastures, the genetic parameters of the weights (P) and weights for age (PE) were estimated from weaning (6 months) to 18 months, with intervals monthly, as well as the average daily gains (G) between weaning and each age. For this, the monthly weighings of 1 441 calves born between 1984 and 1990 were used. The data were analyzed using a linear model that considered the sires as random and the contemporary group as absorbed effect. An increase in the heritability of the three traits was evidenced as the duration of the test increased. Between 6-10 months the heritability was less than 0.20 and between 15-18 months it was higher than 0.30. Genetic correlations between P and between EP at different ages were in the range of 0.5 - 1.0, while among G they were very high from 9 months of age (0.9 - 1.0). In general, the genetic correlations were higher between adjacent ages than as the interval between weighings increased. The phenotypic and environmental correlations were similar in sign and magnitude and lower than the genetic ones. The correlations between G, P and PE were high. It is concluded that in tropical conditions, the same genes that govern the growth rate in different periods up to 18 months of age are, therefore, it is possible to reduce the duration of the test under conditions of handling and feeding similar to those of this study.