Idade e peso no início do teste na análise genética do desempenho de tourinhos Nelore em provas de ganho em peso a pasto

Abstract

The objective of this study was to verify the contribution of the inclusion of initial age and initial weight for genetic analysis of body weight at 550 days of age, average daily gain, linear coefficient of regression of weights according to age, scrotal circumference, testicular volume, and visual scores of body structure, precocity, and muscling of Nellore young bulls on pasture performance tests (PT). Records from 3,193 young bulls were used to estimate genetic parameters in single-trait analysis, with four statistical models. In the first model, fixed effect of PT and the random additive genetic value were included. In the second and third models, the effects of initial age and initial weight were also included as covariates, respectively. In the fourth model, the effects of the two covariates were included. Models without initial age and, or, initial weight as covariates were not adequate. The inclusion of covariates changes the variances, heritability and genetic values. The growth and reproductive traits have moderate heritability and selection can contribute to changing the means of these traits. Morphological traits have low heritability, which suggests that selection is not as efficient to modify the means over time.