Estimation of genetic parameters in dairy production in girolando cattle

Milk production is an important economic activity in Brazil. Dairy farmers would benefit from animal breeding programs that aid in identification and selection of animals with the best cost/benefit ratio to maximize productivity, and additionally provide advice on disposal of less productive animals. This study aims to estimate the heritability and repeatability of milk production corrected for 305 days (PL305) in a herd of Girolando cattle. We analyzed 528 lactations in 251 cows. For the analysis, uniform a priori distribution was defined for systematic effects. Gaussian and inverted Wishart distributions were defined as a priori distributions for random effects. The variance components were estimated based on Bayesian inference using the MCMCglmm function available in the MCMCglmm package of the R software. Convergence was verified with the Geweke test available in the R software. The heritability and repeatability were estimated from the variance component results. Heritability was at 0.28, suggesting that selection for the milk production trait leads to effi cient genetic progress in the herd. Phenotypic variance was mainly due to environmental variance; therefore, the phenotype of individuals should not be considered as indicator for additive genetic variance. Repeatability was at 0.93, indicating that the first performance of the animals based on milk production average is a good indicator of the second, and the data could be used for disposal decisions.