Bayesian model selection of contemporary groups for BLUP genetic evaluation in Latxa dairy sheep

Milk yield data from the Latxa dairy sheep breed were used for model comparison. Three possible models for genetic evaluation, differing in the definition of the contemporary groups, were compared using a Bayesian approach. Contemporary groups were: flock-year+flock-month of lambing-number of parity and age, flock-year-month, and flock-year in models 1, 2, and 3, respectively. All available data from the two strains of the breed (Black-Faced and Blond-Faced) were used. The comparison criteria were: Bayes factor, posterior Bayes factor, pseudo-Bayes factor, two checking functions based on univariate predictive distributions, and the deviance information criteria. The two checking functions consisted in the measure of accuracy (d1) and systematic bias (d2) in the prediction of observations. All criteria except d2 indicated the superiority of model 2 in both strains. Based on these results, it was concluded that model 2 reaches the best equilibrium between fit and predictive ability.