P6004 Estimation of Heritability for Fracture in the Thoroughbred Racehorse

Thoroughbred racehorses can damage several joints and bones due to rigorous training and racing, and develop various fractures during their athletic life. These fractures cause considerable wastage of racing Thoroughbreds. The fracture risk has been shown to be heritable in several species, although fractures in racehorses are generally believed to be influenced by various environmental factors such as speed and truck surface conditions. In this study, we estimated the heritability of the fracture risk in the Thoroughbred racehorse to clarify the genetic factors involved, by using Bayesian analysis with Gibbs sampling based on a categorized model. The clinical data of 3927 racehorses diagnosed by veterinarians of the Racehorse Clinics of Japan Racing Association were used. The health status regarding fractures was categorized as non-fracture, chip-fracture in the carpus, and other types of fractures. The heritability estimate (h2) for non-fracture versus fracture (all types of fractures), obtained from a nonlinear model, was 0.0911. Genetic factors were suggested to be involved in the fracture risk of Thoroughbred racehorses. The heritability estimate for chip-fracture in the carpus (h2 = 0.2598) was much higher than that for the other types of fractures (h2 = 0.0319). These results show that genetic factors relatively contribute to chip-fracture in the carpus, while environmental factors contribute to the other types of fractures. Based on the above results, we are conducting a genome-wide association study (GWAS) to identify candidate genes for chip-fracture in the carpus. At the presentation, we will also report the advances in the GWAS.