Heritability estimates of fractures in Japanese Thoroughbred racehorses using a non‐linear model

Abstract

Thoroughbred racehorses are produced by mating small numbers of Arabian stallions and native British mares, and have been improved by selection of horseracing performance for about 300 years. While these improvements led to good performance as racehorses, they exposed horses to numerous medical disorders, aggravated by extensive exercise. Fractures are frequent medical disorders in Thoroughbred racehorses. In this study, fracture heritability was estimated using 3,927 Japanese Thoroughbred racehorses to elucidate the risk of racehorse fractures. The heritability estimates of all examined fractures were low (h2 = 0.06), while those of fractures in carpal bone and carpus (carpal bone plus distal radius) were moderate (h2 = 0.37, 0.24, respectively). Fracture occurrence age for carpal bone and distal radius was both 3.3 years old and was younger than that for other fractures. These results indicated that a larger proportion of the variation in the studied population was due to genetic factors for carpal fractures than for other fractures, while the fractures at other bones were largely affected by environmental factors, correlated with the athlete period (number year in racing). These findings contribute to develop a management plan for suppressing racehorse fractures and improving horseracing safety.

Fractures in Thoroughbred racing and the potential for pre‐race identification of horses at risk

“…However, a recent systematic review found few associations 86 . The heritability of musculoskeletal injury has been reported from various populations 84,87,88 and evidence that certain genotypes may predispose individual horses to fracture has been obtained from molecular studies, 89 prompting some to speculate that targeted breeding strategies and/or genetic screening might be used to help reduce the incidence of fractures 87–89 …”

“…A genome wide association study on UK Thoroughbreds demonstrated candidate single nucleotide polymorphisms (SNPs) that showed significant relationships to fracture that necessitated euthanasia of the horse 89 . A candidate‐SNP study on Thoroughbred racehorses in Japan found significant associations between the SNPs studied and carpal injuries but not fractures of other limb bones 88 . The relative risk of fracture with different SNPs showed variation between sexes, indicating the complex nature of potential associations between genotype and fracture.…”

“…86 The heritability of musculoskeletal injury has been reported from various populations 84,87,88 and evidence that certain genotypes may predispose individual horses to fracture has been obtained from molecular studies, 89 prompting some to speculate that targeted breeding strategies and/or genetic screening might be used to help reduce the incidence of fractures. [87][88][89] A genome wide association study on UK Thoroughbreds demonstrated candidate single nucleotide polymorphisms (SNPs) that showed significant relationships to fracture that necessitated euthanasia of the horse. 89 A candidate-SNP study on Thoroughbred racehorses in Japan found significant associations between the SNPs studied and carpal injuries but not fractures of other limb bones.…”

“…89 A candidate-SNP study on Thoroughbred racehorses in Japan found significant associations between the SNPs studied and carpal injuries but not fractures of other limb bones. 88 The relative risk of fracture with different SNPs showed variation between sexes, indicating the complex nature of potential associations between genotype and fracture.…”