The inheritance of liability to epistaxis in the southern African Thoroughbred.

The study examines the heritability of the bleeding disorder known as epistaxis in southern African Thoroughbred racehorses, using data from 1986 to 2002. It found that the condition has a strong genetic basis, emphasizing the importance of selective breeding to reduce the risk of epistaxis.

Research Methodology and Data Collection

• The researchers analyzed the data of all horses that suffered from epistaxis, a condition where bleeding occurs from the nostrils, while racing in southern Africa and Mauritius from 1986 to 2002. Around 1252 horses that showed signs of this disorder were included in the study.
• The researchers also considered pedigree data covering the period 1960-1986 to calculate the incidence of bleeding amongst ancestors of the post-1986 horses.
• The study only considered horses that actually raced, as it was impossible to predict whether horses that never raced would have experienced epistaxis had they participated in races.
• All non-runners and those horses that raced in countries where epistaxis data was not recorded were excluded from the study.

Findings of the Study

• According to the data collected, the population incidence of epistaxis in southern African horses was 2.1% during the period investigated.
• The study used the heritability of liability method to estimate the relative importance of heredity and environmental factors influencing the incidence of epistaxis.
• It was found that first-degree relatives had a heritability of 55.4%. This percentage dropped to 41.3% for second-degree relatives and 30.4% for third-degree relatives.
• Notably, horses in the study bled almost exclusively on race days, with only a small percentage reported as having bled during exercise. Hence, the full extent of the condition amongst southern African Thoroughbreds is difficult to estimate strictly.

Conclusions and Recommendations

• While the heritability of liability to epistaxis found in the study is considered at the lower end of the range, the researchers suggest that it could be considerably higher.
• The study concludes that epistaxis in southern African Thoroughbreds has a strong genetic basis.
• It recommends that horses displaying overt bleeding from the nostrils after racing or exercise should be suspended from racing and not used for breeding purposes.
• This selective breeding approach should result in relatively quick progress towards eradicating the disorder from the Thoroughbred population, addressing this major health concern for the racing industry.