Estimativa de parâmetros genéticos, componentes de (co)variância e tendências genéticas e fenotípicas para características produtivas pré-desmama em bovinos Devon no Rio Grande do Sul

Abstract

Revista Brasileira de Zootecniabivariadas relacionando os pesos, tanto ao nascer quanto à desmama, ao ganho de peso pré-desmama. As herdabilidades e os erros-padrão obtidos das análises univariadas foram de 0,32 ± 0,03 para PN, 0,17 ± 0,01 para GNDA e de 0,12 ± 0,01 para PD. Nas análises bivariadas do PN com GNDA e do PD com GNDA, as herdabilidades obtidas foram de 0,35 e 0,17 e de 0,32 e 0,42, respectivamente. Os resultados demonstram, pelas herdabilidades médias para os pesos e ganhos de peso, que essas características podem responder de forma eficiente à seleção. As correlações genéticas, alta (0,95) entre PD e GNDA e baixa (0,15) entre PN e GNDA, demonstram que, ao selecionar pelo ganho, é possível obter uma resposta correlacionada no peso à desmama sem acarretar incremento no PN. As tendências genéticas e fenotípicas obtidas demonstram a ocorrência de progresso genético para as características de GNDA e PD, enquanto PN apresenta-se em platô, indicando, portanto, mudança favorável no desempenho pré-desmama, sem aumento no risco de problemas de parto.Palavras-chave: correlações, efeito materno, herdabilidade, pré-desmama Estimation of genetic parameters and (co) variance components for preweaning productive traits in Devon Cattle in Rio Grande do SulABSTRACT -The objective of this study was to estimate (co)variance components and genetic parameters, such as heritabilities and correlations, and genetic and phenotypic trends for birth weight (PN), weaning weight (PD) and 205 day adjusted weight gain (GNDA). A total of 23,369 records on animals, born from 1980 through 2000, collected by PROMEBO -beef cattle improvement program of Associação Nacional de Criadores Herd Book Collares, were used. Of these animals, 16,593 had record of PN, 22,530 had of PD and 22,259 of GNDA. Analyses were performed by the restricted maximum likelihood method using the MTDFREML program. Initially, a univariate analysis was used for each trait and, afterwards, bivariate models were used in analyses relating weights at birth and weaning with pre-weaning gain.Heritabilities and standard errors obtained from univariate analyses were of 0.32 ± 0.03 for PN, 0.17 ± 0.01 for GNDA and of 0,12 ± 0,01 for PD. From bivariate analyses of PN with GNDA and of PD with GNDA, heritability estimates were of 0.35 and 0.17 and of 0,32 and 0.42, respectively. Medium heritabilities for weights and weight gains indicate that these traits efficiently respond to selection. Genetic correlation estimates was high (0.95) between PD and GNDA and low (0.15) between PN and GNDA indicating that selection for weight gain make it possible to obtain a correlated response on weaning weight, without increasing birth weight. Estimated genetic and phenotypic trends demonstrated genetic progress for GNDA and PD, while PN is on plateau, thereby, indicating favorable change in pre-weaning performance, without increasing risk of calving difficulty.

Direct and maternal annual genetic changes for selected traits at weaning and yearling in beef cattle

“…The mean of genetic change estimated for BWG was slightly lower than that reported by Laureano et al (2011) for Nellore animals, with value of 0.186 kg year -1 . On the other hand, Fernandes, Ferreira, and Rorato (2002) and Corrêa, Dionello, and Cardoso (2006) for Charolais and Devon breeds, respectively, reported annual genetic changes lower than the value estimated in this study, with values of 0.041 kg and 0.047 kg, respectively. Genetic variations and differences in the selection criteria adopted, including different weights for the traits included in the selection indices, contribute to obtain varied genetic gains among populations.…”

Genetic parameters and phenotypic and genetic trends for weight at weaning and visual scores during this phase estimated for Angus-Nellore crossbred young bulls

“…The maternal genetic trend found in this study was -312.0 g/year, lower than that reported by Corrêa et al (2006) for the Devon breed (-23.6 g/year). Obtainment of negative estimates for the maternal genetic trend was due to the finding of negative correlation between direct effects and maternal effects (Table 2), indicating inversely proportional quantities, however, in this regard, it should be considered the previously commented arguments by Schaeffer (1996).…”

“…The direct genetic trend (Figure 2a) was 221.0 g/year, with value higher than those obtained by Corrêa et al (2006) for the Devon breed, of 55.1 g/year, but similar to that of 220.9 g/year obtained by Weber et al (2009) for the Aberdeen Angus breed, indicating that the direct genetic gain in the years studied in this population is improving. The maternal genetic trend found in this study was -312.0 g/year, lower than that reported by Corrêa et al (2006) for the Devon breed (-23.6 g/year).…”

Parâmetros e tendências genéticas para pesos de várias idades em bovinos Nelore

“…A característica P205 (Figura 2) apresentou declínio médio ao longo do período de -0,045 kg por ano assim como para a característica P365, com redução anual de -0,007kg (Figura 5). Esse comportamento se deve, segundo Correa et al (2006), à correlação negativa entre o efeito direto e efeito materno, visto que, o efeito materno diminui a medida que o efeito direto aumenta. Gonçalves et al (2011) ressaltam que este fato é esperado, uma vez que se é dada ênfase (seleção) para as características de produção (desempenho ponderal etc.).…”