Breed predisposition and heritability of atrial fibrillation in the Standardbred horse: a retrospective case-control study.

The research is a retrospective study investigating the genetic predisposition and heritability of atrial fibrillation in Standardbred horses, using data from the Ontario Veterinary College Health Sciences Centre between 1985-2009. The results indicate a significant genetic component in the occurrence of atrial fibrillation in this breed, suggesting the need for further genomic studies.

Introduction and Methodology

• The study aims to determine if there are genetic factors contributing to atrial fibrillation (AF), a common heart condition, in Standardbred horses. This was a retrospective case-control study which compared Standardbred horses that had been diagnosed with AF with those that hadn’t.
• Data was gathered from the Ontario Veterinary College Health Sciences Centre (OVCHSC) spanning a 24-year period from 1985-2009. The analysis involved more than 40,000 horses, of which 396 had a diagnosis of AF.
• The researchers calculated heritability and inbreeding coefficients and examined the breed and year effects on AF diagnosis. They also calculated the odds ratios for AF in relation to frequently occurring sires (male parents).

Findings

• The researchers found that the effects of breed and year on AF diagnosis were highly significant. From 1997 onwards, the breed effect was primarily due to Standardbred admissions. This suggests that the rate of AF diagnoses in Standardbred horses increased over the studied period.
• Compared to other horse breeds, Standardbreds were more likely to present with AF, indicating a breed predisposition. Conversely, Quarterhorses were significantly less likely to be affected.
• The researchers also found that AF’s heritability estimates were consistent over the study period, with estimates around 10% on the observed binomial scale and about 30% on the underlying scale.
• Of 22 sires that appeared more than 10 times in the case/control file, eight of them were found to produce offspring with AF more frequently than expected, indicating a potential genetic influence. However, inbreeding was not identified as a significant factor.

Conclusions

• This study indicates that there is a genetic liability to AF in Standardbred horses. However, it suggests that the genetic basis of AF in these horses is likely complex, and not due to single genes with simple Mendelian inheritance.
• Given these findings, the researchers concluded that more detailed genomic studies are required to understand the specific genetic factors contributing to the incidence of AF in Standardbred horses.