Risk Factors for Epistaxis in Thoroughbred Flat Races in Japan (2001–2020)

SIMPLE SUMMARY: Epistaxis (bleeding from the nostrils) can be caused by exercise-induced pulmonary hemorrhage (EIPH) in Thoroughbred racehorses. EIPH is a common disease in racehorses and 55–75% of horses experience EIPH after racing. In addition, horses with severe EIPH are likely to have poor performance compared to horses without EIPH. The risk factors have been surveyed by several reports, but the results may vary. This retrospective study aimed to identify the risk factors for epistaxis in Japanese flat races between April and September, from 2001 to 2020. Nine factors were significantly associated with epistaxis, including racecourse, body weight, ambient temperature, age, sex, surface condition, racing distance, training center, and race year. While 7 of the factors have been considered in previous studies, we have confirmed that the location of the racecourse and a higher body weight can affect the incidence of epistaxis. ABSTRACT: We investigated the risk factors for epistaxis in Japanese flat races over a 20-year period. The veterinary records of horses identified as having epistaxis by endoscopy on the race day, and the official racing records of all flat races from April to September between 2001 and 2020, were reviewed. The racecourses (n = 10), surface type, surface condition, race class, race distance, race year, sex, age, two training centers, ambient temperature, and body weight on race days were assessed using multivariable logistic regression (p < 0.05). Of 475,709 race starts, 616 (1.30 cases per 1000 starts; 95% confidence interval [CI], 1.20–1.40) included an epistaxis event. Nine variables were significantly associated with epistaxis. Seven of the variables have been reported in previous studies: lower ambient temperature, soft surface conditions, shorter racing distances (≤1400 m), increasing age, females and geldings compared to males, training center, and race year. However, two novel variables were identified as significantly associated with epistaxis, increasing body weight per 20 kg (p < 0.001, odds ratio [OR], 1.33; 95% CI, 1.25–1.41) and the racecourses that the horses were running at (p < 0.001, especially Sapporo [OR; 4.74, 95% CI, 3.07–7.31], Hakodate [OR, 4.66; 95% CI, 3.05–7.11], and Kokura [OR, 4.14; 95% CI, 2.65–6.48] compared to the reference racecourse [Kyoto]). These results can facilitate developing interventions to reduce epistaxis in flat racing.