Componentes de (co)variância e parâmetros genéticos de caracteres pós-desmama em bovinos da raça Angus

Abstract

RESUMO -Foram determinados os componentes de (co)variância para caracteres do período pós-desmama na raça Angus e de covariância com peso ao nascer (PN) e caracteres do período pré-desmama por intermédio de um modelo animal. Utilizaram-se dados de 18.921 animais com registros de peso à desmama e ao sobreano, dos quais 4.452 tinham avaliações completas para escores visuais à desmama e ao sobreano. Registros de PN estavam disponíveis para 11.788 animais. As herdabilidades do ganho de peso pós-desmama (GP205) e dos escores de conformação (CS), precocidade (GS), musculatura (MS) e tamanho (TS) ao sobreano foram de 0,20, 0,19, 0,25, 0,26 e 0,24 respectivamente. As correlações genéticas entre os caracteres estudados foram todas positivas: entre GP205 e escores visuais variaram de 0,50 a 0,71; para os escores ao sobreano entre si, de 0,22 a 0,94; entre GP205 e PN foram de 0,14; entre GP205 e ganho pré-desmama, de 0,23; e para o mesmo escore visual observado à desmama e ao sobreano, de 0,90 a 0,99. Esses resultados indicam que é possível selecionar para GP205, sem aumento importante do PN, e que a seleção para GP205 deverá promover uma mudança genética correlacionada em escores visuais ao sobreano.Palavras-chave: Angus, bovinos de corte, correlação genética, herdabilidade, período pós-desmama (Co)Variance Components and Genetic Parameters of Post-Weaning Traits in Angus CattleABSTRACT -(Co)variance components were determined for post-weaning traits, and covariances with birth weight (BW) and preweaning traits, in Angus cattle using an animal model. Records of weaning and yearling weights of 18,921 animals were used and from these 4,452 had complete evaluations of visual scores at weaning and post-weaning phases. Records of BW were available for 11,788 animals. Heritabilities of post-weaning gain (GP205) and visual scores for conformation (YC), precocity (YP), muscling (YM) and size (YS) were 0.20, 0.19, 0.25, 0.26 and 0.24, respectively. Genetic correlations among all traits considered were positive: between GP205 and visual scores the range was from 0.50 to 0.71; for yearling scores among themselves from 0.22 to 0.94; between GP205 and BW was 0.14; between GP205 and pre-weaning gain was 0.23 and for the same score at weaning and yearling stages they varied from 0.90 to 0.99.These results indicate that it is possible to select for GP205 without a significant increase in BW and that the selection for GP205 should produce a correlated genetic change on yearling visual scores.

Estimates of genetic parameters for visual scores and daily weight gain in Brangus animals

“…This hypothesis is supported by the environmental correlation estimate between GBW and GWY (20.17 6 0.016; Table 5), indicating weak antagonism between environmental and non-additive genetic effects that act on the two traits. However, this result agrees with Cardoso et al (2004), Marcondes et al (2000) and Sarmento et al (2003) who reported genetic correlation estimates of 0.23, 0.23 and 0.22, respectively, between pre-and postweaning weight gains.…”

“…Similar genetic correlations have been reported by Koury Filho (2001) for Nelore animals. In contrast, Cardoso et al (2004) estimated higher correlations for Angus cattle.…”

“…In the literature, this association was only reported by Cardoso et al (2004), who obtained correlations between scores stronger than 0.90 in the Angus animals. Correlation estimates between the different scores obtained at weaning and yearling were also strong (.0.63; Table 5).…”

“…In this respect, Cardoso et al (2004) estimated genetic correlations ranging from 0.22 to 0.94 between the reported scores at 550 days, whereas these estimates ranged from 0.50 to 0.71 when correlated with weight gain from birth to weaning. On the other hand, the genetic correlation between the same visual scores observed at weaning and yearling age ranged from 0.90 to 0.99.…”

“…Dal-Farra et al (2002) suggested that selection based on C, P and M scores may be sufficient as long as the heritability estimates for -E-mail: saquei@fcav.unesp.br these traits are similar to the estimates for weight gain. Cardoso et al (2004) estimated heritabilities of 0.19, 0.25 and 0.26 for yearling C, P and M scores, respectively, in Angus cattle.…”