Using conformation traits to improve reliability of genetic evaluation for herd life based on survival analysis

Genetic evaluation for herd life based on survival analysis utilizes information available on all animals, dead (uncensored) and alive (censored), but the reliability of bulls' breeding values depends only on the number of uncensored daughters. Therefore, information on correlated conformation traits scored on daughters during their first lactation may be essential for the evaluation of young bulls with mostly censored daughters. Currently available programs for genetic evaluation based on survival analysis cannot combine indirect information on conformation traits with direct information on herd life, nor can they estimate genetic covariances between herd life and conformation traits. In this study, an alternative approach has been developed and tested using data on Swiss Simmental and Red & White cattle. Genetic covariances were approximated using breeding values for herd life from a survival analysis and BLUP breeding values for 26 linear conformation traits from a separate multivariate analysis. An index combining direct breeding values for herd life and indirect breeding values obtained from conformation traits was constructed. The relative weighting of both information sources varied depending on the amount of available information. The maximum reliability based only on conformation traits was 0.64. Except for old bulls with >100 uncensored daughters, the combined reliability was always higher than the direct reliability from survival analysis.