Risk factors for exertional heat illness in Thoroughbred racehorses in flat races in Japan (2005-2016).
Authors: Takahashi Y, Takahashi T
Journal: Equine veterinary journal
Summary
# Exertional Heat Illness in Racing Thoroughbreds: Identifying High-Risk Conditions Between 2005 and 2016, Japanese veterinary records identified 194 cases of exertional heat illness (EHI) in flat-racing Thoroughbreds, with 188 occurring during the April–September period when researchers conducted their case-control analysis using wet-bulb globe temperature (WBGT) indices and race data. Environmental heat burden emerged as the dominant risk factor: when WBGT exceeded 28°C, horses faced a 28.5-fold increased risk of EHI compared to conditions below 20°C, with July showing the highest incidence at 1.1 cases per 1000 starts. Beyond thermal stress, several intrinsic factors substantially elevated vulnerability: geldings and mares carried 4.9- and 2.4-fold higher risk respectively than entire males, whilst horses aged four years and older showed 3.5–3.9-fold increased susceptibility, and lighter bodyweight animals demonstrated greater susceptibility with each 20 kg reduction conveying increased odds of illness. Longer race distances (>1600 m) were also protective against EHI, suggesting that sprint races at high temperatures present particular hazard. These findings provide evidence-based parameters for racecourse management—specifically WBGT monitoring, scheduling races during cooler periods, and heightened vigilance for older, lighter or female horses—allowing racing stakeholders to implement targeted risk mitigation strategies during warm-weather months.
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Practical Takeaways
- •Monitor WBGT conditions closely during racing season (April-September) and consider reducing race intensity or scheduling when WBGT exceeds 28°C to prevent EHI in your racehorses
- •Be aware that geldings and mares have significantly higher EHI risk than intact males; implement enhanced cooling protocols and careful conditioning for these horses during hot months
- •Assess individual horse risk based on age, bodyweight, race distance and sex; older, lighter-framed horses and females are particularly vulnerable and warrant extra precautions
Key Findings
- •Highest EHI incidence occurred in July at 1.1 cases per 1000 starts
- •WBGT index exceeding 28°C increased EHI risk 28.5-fold compared to <20°C (P<0.001)
- •Geldings and females were 4.9× and 2.4× more likely to develop EHI than uncastrated males respectively
- •Longer races (>1600 m), older horses (4+ years), and lower bodyweight were independent risk factors for EHI