engleski

Evaluation of G × E in Angus cattle by using reaction norms

Animal performance varies due to the influence of genotype by environment interaction (GxE). The purpose of this study was to determine the magnitude of GxE by fitting reaction norms in models for estimating heritabilities of growth traits in U.S. Angus cattle. Weights at birth (BW), 205 d (WW), and 365 d (YW) were adjusted according to American Angus Association guidelines. Environments were defined as progeny groups from a common herd. For data to be included, the following criteria had to be met: each bull must have had at least 100 progeny, with at least six progeny per environment, in at least five environments per bull, and at least six bulls having progeny in each environment. The mean performance of all progeny within each herd environment was defined as the environmental mean. Mean performance of progeny of a sire within an environment was defined as the progeny mean. Four statistical models were evaluated for estimation of heritabilities. All models included year–season, contemporary group (processing date and lot id), and sex as fixed effects. Herd environment was fitted as a categorical effect in models designated CM and GEM. Environmental means were fitted as a continuous effect in models designated CEM and RRM. Models CM and CEM included sire as a random variable. Model GEM included sire and sire x herd environment interaction as random variables. Model RRM included reaction norms of each bull calculated by regressing progeny means on environment means. Regression coefficients from RRM were fitted to an ANOVA model including bull and environmental mean. Model fit statistics indicated RRM had the best fit. Heritability estimates ranged from 0.293 to 0.401 for BW ; 0.141 to 0.289 for WW ; and 0.147 to 0.259 for YW across all models. Regression coefficients differed among bulls for all traits (P< 0.0001). Rank correlations between environments depicted re-ranking of bulls. These results suggest that bulls differ in the consistency of their progeny′s performance across environments. Estimates of genetic merit of regressions from reaction norms may be a useful selection tool for ranking bulls to be used across diverse environments.

beef cattle; GxE; reaction norm

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