Author(s): SUGIYAMA, F., MUKAI, K., TAKAHASHI, Y., EBISUDA, Y., YOSHIDA, T., Institution: JAPAN RACING ASSOCIATION, Country: JAPAN, Abstract-ID: 764

INTRODUCTION:
Thoroughbred flat races involve distances of 1,000-2,600 m and an approximate speed of 60 km/h, such that they are completed in only 1-3 minutes. Similar to human athletes, sudden cardiac death (SCD) has been reported in Thoroughbred racehorses, and it is one of the most common causes of fatality during races, second only to musculoskeletal disorders. Previous studies have identified some risk factors for SCD, such as age and season, whereas the results regarding other potential factors, such as race distance, have been conflicting (1, 2). Given the variation in horse populations and racing systems among horse-racing jurisdictions, individual assessments of these risk factors for SCD are essential. However, there have been no studies of the risk factors for SCD in Japan. Therefore, we aimed to analyze the incidences of SCD and the associated risk factors in Japanese Thoroughbred flat racing.
METHODS:
Race information and the veterinary records for thoroughbred horses competing in flat races held by the Japan Racing Association (JRA) between 2001 and 2022 were collected from the official database, and a retrospective unmatched case-control study was conducted to identify the risk factors for SCD. Horses that were diagnosed with “acute heart failure” or “heart failure” at JRA racecourses were defined as SCD cases, whereas horses that were not were regarded as controls. Age, sex, body weight, track condition, surface type, race class, race distance, season, and training center were included as variables in the analysis. Variables were initially analyzed by a combination of forward- and backward-stepwise procedures and were included in the final model if P ≤ 0.2. Multivariable logistic regression analysis was then performed to identify the risk factors for SCD, and variables with P < 0.05 were considered to be statistically significant.
RESULTS:
During the study period, data for 1,039,096 race starts were extracted, and 81 cases of SCD were identified (prevalence 0.006%). Of the nine variables considered, five were included in the final model. Body weight was significantly associated with SCD (P = 0.047), but age (P = 0.051), race class (P = 0.069), sex (P = 0.141), and surface type (P = 0.146) were not. Compared with horses weighing ≤ 449 kg, the odds ratio for SCD for horses weighing ≥ 490 kg was 2.33 (95% confidence interval 1.08-5.05).
CONCLUSION:
In Japan, the incidence of SCD during flat races is comparable to that previously reported (1, 3). In contrast to previous studies (3, 4), age and race distance were not found to be significant risk factors for SCD. However, body weight was significantly associated with SCD, which may provide a novel perspective regarding the etiology of SCD in Thoroughbred racehorses.

References
1. Lyle, et al, Equine Vet J (2010)
2. Bennet et al, J Am Vet Med Assoc (2022)
3. Gibson, et al, Animals (2023)
4. Nath et al, Animals (2022)