Heritability estimates of atrial fibrillation in Thoroughbred racehorses in Hong Kong and Australia.

The study investigated the possibility of a genetic component in the development of atrial fibrillation, a common heart condition affecting racehorse performance, in Thoroughbred racehorses. The findings suggest a low level of heritability, indicating other factors, possibly environmental or individual, might be more significant contributors to the condition.

Study Overview

• The objective of this study was to determine if there’s a genetic contribution to atrial fibrillation (AF) in Thoroughbred racehorses, a concept previously suggested for Standardbred racehorses.
• Two subsets of Thoroughbred racehorses racing from 2007 to 2019 in Hong Kong and Australia were used: horses with detected AF post-race (463 cases) and their randomly chosen racing counterparts without AF (2,315 controls).

Methodology

• The ASReml-R program was used to fit an animal model to the AF data, which allowed the researchers to estimate heritability.
• A subset of 106 horses that had electrocardiographic confirmation of AF was examined separately.
• Variance components were calculated while assuming AF was either normally distributed or logit-transformed.
• The risk of producing AF-affected offspring was also calculated for stallions that sired 10 or more individuals in both the case and control populations, using Fisher’s exact test.

Results

• The estimated heritability of AF among the entire population of Thoroughbred horses was fairly low, ranging from 0.064 to 0.071.
• In the subset of horses with electrocardiographically confirmed AF, heritability estimates were similarly low, ranging from 0.058 to 0.065.
• Among the 71 stallions that sired 10 or more individuals, three were more likely to produce affected offspring, with an odds ratio ranging from 4.05 to 7.57.
• However, age, sex, and year of birth did not contribute to the expression of AF.

Conclusions

• Even though some stallions were more likely to produce affected offspring, the heritability of AF within this population of Thoroughbred horses was low.
• This suggests that other factors, potentially environmental or individual-related, may be major contributors to the development of AF in these horses, necessitating further research into these areas.