Tendência genética para características relacionadas à velocidade de crescimento em bovinos Nelore da regi?o norte do Brasil

摘要

The objective was to estimate the (co) variance, genetic parameters and trends for the characteristics, days to gain 160 kg (D160) in the pre-weaning phase, and days to gain 240 kg (D240) in the post-weaning phase, in Nellore cattle, grown in Northern Brazil. Records analyzed were of animals raised on pasture in northern Brazil, provided by the Brazilian Association of Zebu Breeders - ABCZ, and collected from 1997 to 2007. Contemporary groups (herd, year, birth season and gender) were used as a fixed effects model, and age at calving as a covariant. Estimates of (co) variance were obtained using the MTDFREML software. The averages observed for D160 and D240 were 235 ± 46 days and 578 ± 171 days respectively. Estimates of heritability for D160, due to the additive genetic and maternal effect, were 0.27 ± 0.03 and 0.35 ± 0.04, respectively. For D240, the heritability for the additive genetic effect was 0.28 ± 0.03. This indicates that selection for any of the characteristics will result in genetic progress. Potential genetic gains due to the additive genetic effect, were 1.02 and 3.17 days per year for D160 and D240 respectively. This corresponds to 0.43 and 0.55% of the average of days to gain 160 kg (pre-weaning) and 240 kg (post-weaning) respectively. Although weight is currently used as the selection criteria, the genetic trends for D160 and D240 indicated the existence of genetic progress when using these characteristics as the selection criteria.