Records on 105 465 Nellore calves born from 1977 to 1994 in eight regions of Brazil were studied to evaluate the effects of genotype x environment interaction on weaning weight of calves. The interactions were estimated by the genetic correlations of weaning weight in different regions. To estimate the variance and covariance components to obtain the genetic correlation of weaning weight under different regions, a sire model and MTDFREML software were used, for two regions each time. The mathematical model included the fixed effects of year(17) and month(12) , sex(2) of calf, farm(419) and age of dam (covariable), and the random effect of sire (588) and dam (57 162). The sire components of variance for each of the regions where 20.33, 28.08, 17.72, 29.80, 34.36, 38.08, 37.72 and 21.44. The phenotypic component were 375.11, 430.87, 430.65, 406.63, 408.99, 400.44, 412.71 and 335.74; for regions one two eight, respectively. The genetic correlations of weaning weight for two region at a time were generally low, indicating the presence of genotype x environment interaction.
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