Estimates of heritability of atrial fibrillation in the Standardbred racehorse.

The research article looks into the heritability of atrial fibrillation (AF) in Standardbred racehorses, suggesting that the arrhythmia may have a genetic component in this breed, with a higher occurrence in males and pacers.

Study Objective and Methodology

• The main objective of the study conducted by Ontario Veterinary College Teaching Hospital was to evaluate if atrial fibrillation (AF) – a heart condition characterized by irregular and often rapid heart rate – has a genetic heritability in Standardbred horses. The researchers were also interested in knowing whether this heritability differs across gaits (the way a horse moves) and sexes.
• A retrospective review was carried out where clinical records, pedigree details, and racing records of Standardbred horses, born between 1978 and 2007, were studied. The study focused on horses that were admitted to the hospital for treatment of AF.
• A total of 204 cases were identified and used as the study group. For the control group, five sex- and gait-matched horses that were assumed not to suffer from AF were identified for each case by examining race records from the six months prior to each case’s admission. This brought the control group to a total of 1017 horses.
• The heritability was estimated for the whole cohort, and then calculated separately for both sexes and gaits, using a generalized linear mixed model.

Research Findings and Conclusion

• As per the data gathered, the heritability of AF on the underlying liability scale across the entire dataset was estimated to be 0.30±0.04, while for males it was 0.30±0.06, for females 0.24±0.08, and for pacers, it was 0.32±0.05.
• After converting these estimates to the observed scale, the heritability figures were recorded as 0.14, 0.15, 0.09, and 0.15, respectively for the entire dataset, males, females, and pacers.
• For trotters – another gait variant in horses – there wasn’t enough data to estimate the heritability of AF.
• The research concluded that there was a moderate level of heritability of AF in Standardbred horses, which was particularly more evident in males and pacers. This leads to the hypothesis that the arrhythmia in this breed may be genetically influenced.