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 r acing 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 repeatabilit y animal model using each individual start of trotters and pedigree informa tion of up to I I generations (13,202 horses). Besides the driver effect, t he 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 anal ysed were square root of rank at finish, racing time per kin and the logari thms of earnings per start. Ignoring the effect of driver resulted in an ov erestimation of heritability of 60, 24 and 44% for rank at finish, racing t ime and earnings, respectively, which shows the necessity to include the dr iver effect in the model. Drivers regarded as fixed or random effects resul ted in a marginal change in parameters. Heritabilities based on the model w ith fixed driver effect were 0.05, 0.29 and 0.09 for ranks at finish, racin g time and earnings, respectively. Genetic correlation between rank and rac ing time was 0.81. Both traits were highly correlated with earnings of -0.9 8 and -0.89 for ranking and racing time, respectively. Most important trait for selection of racing performance was the racing time due to its substan tial higher heritability and its high genetic correlation to earnings. Addi tionally, 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.