Abstract
Six alternatives of contemporary group (CG) definition for the genetic evaluation of weaning weight of Braunvieh cattle in Mexico were evaluated. Different alternatives of CG definition were formed by combining three minimum CG sizes (3, 7 or 10 records) and its consideration either as a fixed or random effect. The models included the direct and maternal genetic effects, their covariance, and permanent environment as random effects, and the linear and quadratic effects of cow age at calving as a covariate. The CG were formed by combining the effects of year and season of birth, calf's rearing condition, herd, and calf sex. The six alternatives of CG definition were compared using the descriptive statistics of the predicted breeding values and their accuracies, (co)variances and genetic parameters, and both the correlation between the predicted breeding values, and between their corresponding accuracies. On average, the accuracies of the direct genetic effects were slightly higher when CG was considered fixed than when it was fitted as random effect. For the maternal genetic effects there was no difference. The highest accuracies were obtained with a CG size of at least seven records. For both, the direct and maternal genetic effects, the CG size of seven records produced the highest heritability estimates, regardless of CG being fitted as fixed or random effect. The best alternative of contemporany group definition was a minimum of seven records and its inclusion as a fixed effect in the model for the genetic evaluation of this breed in Mexico.
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