Estimation of Genetic Parameters for Daily Gains of Bulls with Multi-Trait and Random Regression Models

Abstract. The average daily gains of 6,420 Czech Pied bulls (dual-purpose, Simmental type) from 7 breeding stations were analyzed using single-trait animal models, a multi-trait animal model and random regression models. The effects of station, year and season were taken into account by creating herd-year-season classes (HYS) with the season being defined as a 3-month class starting with December. Legendre polynomials of the 1st to the 4th degree were used to describe the daily gains within the HYS classes as well as to model bull-specific gain curves. The comparison of the h²-values estimated with single-trait models and those gained with a multi-trait model returned only insignificant differences. The comparison of genetic parameters based on the multi-trait model to those from different random regression models shows that polynomials of at least the 2nd degree are to be used for the genetic analysis of daily gains.