Are racehorses born unsound?

A new study out of Hong Kong completed in conjunction with the Animal Health Trust in England and the University of Glasgow seems to suggest a heritable genetic component to some forms of injury. Here is the abstract...

A retrospective cohort study of important musculoskeletal conditions of Thoroughbred racehorses was conducted using health records generated over a 15 year period (n = 5062, 1296 sires). The prevalence of each condition in the study population was: fracture, 13%; osteoarthritis, 10%; suspensory ligament injury, 10%; and tendon injury, 19%. Linear and logistic sire and animal regression models were built to describe the binary occurrence of these musculoskeletal conditions, and to evaluate the significance of possible environmental risk factors. The heritability of each condition was estimated using residual maximum likelihood (REML). Bivariate mixed models were used to generate estimates of genetic correlations between each pair of conditions.

Heritability estimates of fracture, osteoarthritis, suspensory ligament and tendon injury were small to moderate (range: 0.01–0.20). Fracture was found to be positively genetically correlated with both osteoarthritis and suspensory ligament injury. These results suggest that there is a significant genetic component involved in the risk of the studied conditions. Due to positive genetic correlations, a reduction in prevalence of one of the correlated conditions may effect a reduction in risk of the other condition.

While the heritability estimates are quite low, it is worth noting that they are looking at Hong Kong, where the pre-purchase examination standards of horses imported into that country are very high so it is possible that the representatives of each sire/sireline imported are among the more sound of their offspring. That said, the paper was still able to ascertain that there is a significant genetic component to fracture rates other forms of unsoundness in racehorses.

The obvious next question is, where (in terms of country) is the source of this unsoundness?