Genetic analysis of distance-dependent racing performances in German Thoroughbreds

Abstract. The objective of this study was to develop a new multivariate statistical model for genetic estimation of distance-dependent racing performances in German Thoroughbreds. Analysed performance traits were »square root of distance to first placed horse in races over sprint distances (until 1 400 m)«, »square root of distance to first placed horse in races over mile distances (from 1 401 m to 1 900 m)« and »square root of distance to first placed horse in races over long distances (over 1 900 m)«. These traits were found to be influenced by the carried weight, which was determined by the horses’ earlier performance. Therefore, new traits were developed based on random regression models, which were independent from the carried weights. Genetic parameters were first evaluated for these new created traits »new distance to first placed horse in races over sprint distances« (h²=0.088), »new distance to first placed horse in races over mile distances« (h²=0.081) and »new distance to first placed horse in races over long distances« (h²=0.137) using a multivariate animal model. Genetic correlations between these traits were high, but differed from r_g=1. A further heritability was estimated for the distance-independent trait »new distance to first placed horse in races over all distances« (h²=0.101) applying a univariate animal model with a fixed distance effect. These two different models were compared by two criteria. The ranking of breeding values for the distance-independent trait (estimated with the univariate model) was first correlated with each of the rankings of breeding values for the three distance-dependent traits (estimated with the multivariate model). Correlations varied from r=0.668 to r=0.813. The second criterion for comparison was the percentage of incorrectly selected raced stallions by breeding values estimated with the univariate model. Between 47.4 % and 69.7 % of stallions were incorrectly selected. The use of a total selection index including breeding values of the three distance-dependent traits with suitable weightings was recommended as a possible future selection criterion.