Multiple-trait genetic analyses of racing performances of German trotters with disentanglement of genetic and driver effects

The objectives of this study were the analysis of the effect of driver on racing performances of trotters and development of a genetic model in order to estimate genetic parameters for German trotters. Data on 6,611 trotters with 163,322 records during 1997 and 1999 were analysed with a repeatability animal model using each individual start of trotters and pedigree information of up to I I generations (13,202 horses). Besides the driver effect, the genetic model included year-season, age and sex of trotter, racing track, distance and condition of race track as fixed effects as well as additive genetic and permanent environmental effects as random effects. Traits analysed were square root of rank at finish, racing time per kin and the logarithms of earnings per start. Ignoring the effect of driver resulted in an overestimation of heritability of 60, 24 and 44% for rank at finish, racing time and earnings, respectively, which shows the necessity to include the driver effect in the model. Drivers regarded as fixed or random effects resulted in a marginal change in parameters. Heritabilities based on the model with fixed driver effect were 0.05, 0.29 and 0.09 for ranks at finish, racing time and earnings, respectively. Genetic correlation between rank and racing time was 0.81. Both traits were highly correlated with earnings of -0.98 and -0.89 for ranking and racing time, respectively. Most important trait for selection of racing performance was the racing time due to its substantial higher heritability and its high genetic correlation to earnings. Additionally, rank at finish has to be included in the breeding goal because it reflects more the potential of trotters to win at finish and accounts for records without earnings.