Risk factors for exertional heat illness in Thoroughbred racehorses in flat races in Japan (2005–2016)

Abstract

Summary Background Exertional heat illness (EHI) is recognised in horses, but few reports have investigated its risk factors. Objectives To identify risk factors for EHI in racehorses participating in flat races in Japan. Study design Descriptive epidemiology and retrospective unmatched case–control study. Methods Between 2005 and 2016, veterinary records of horses diagnosed with EHI after flat races were reviewed retrospectively and data of the months from April to September were used for a case–control study. For each case, three control horses were randomly selected from starts between April and September. Race records of horses and estimated wet‐bulb globe temperature (WBGT) indexes at the local meteorological observatory closest to the racecourse were investigated. To identify risk factors for EHI, univariable and multivariable logistic regression analysis was used. Results Of 194 cases during the study period, 188 cases occurred between April and September. The highest incidence risk was in July (1.1 cases per 1000 starts, 95% confidence interval 0.84–1.45). In the final multivariable model, WBGT index, sex, race distance, age and bodyweight were associated with EHI. When WBGT index exceeded 28°C, the risk of EHI was considerably higher than <20°C (OR 28.5, 14.2–62.4, P<0.001). Compared with uncastrated males, geldings (OR 4.9, 1.8–13.3, p = 0.002) and females (OR 2.4, 1.5–3.7, P<0.001) were at high risk of EHI (P<0.01). Furthermore, races of >1600 m (OR 1.8, 1.2–2.8, P = 0.002), 4‐year‐old (OR 3.5, 1.6–7.9, P = 0.002) and ≥5‐year‐old (OR 3.9, 1.8–9.2, P = 0.001) horses and horses with low bodyweight (OR per 20 kg, 0.8, 0.7–1.0, P = 0.02) were associated with increased risk of EHI. Main limitations The median straight‐line distance between the racecourse and the local meteorological observatory was 14.2 km (range, 1.1–28.3 km). There was a lack of objective criteria of EHI due to the retrospective nature of the study. Conclusions We identified specific risk factors for EHI in racehorses. These results may be useful to the equine industry for reducing EHI occurrence in racehorses.

Effects of Pre-Cooling on Thermophysiological Responses in Elite Eventing Horses

“…This likely supported cooling the skin down and attenuating the rise in T rump . Such differences in physiological responses between testing days are not surprising considering previous equine research, concluding that the number of exertional heat illness cases was significantly higher when WBGT was 20-23.9 • C (~day 2 of the present study) compared to <20 • C (~day 1 of the present study) [30].…”

Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies

“…Exertional heat illness (EHI) in horses is characterized by severe central nervous system dysfunction, such as physical collapse, and has been described in detail ( Brownlow et al, 2016 ; Brownlow and Mizzi, 2020 ). Recently, a Japanese study identified a wet-bulb globe temperature (WBGT) index above 28°C to be responsible for a 28.5% higher risk for development of EHI when compared to the index below 20°C ( Takahashi and Takahashi, 2020 ). A progressive increase in the prevalence of human EHI casualties is anticipated due to global warming ( Raymond et al, 2020 ) and a similar effect can be anticipated for animals in general.…”

An investigation into environmental variables influencing post‐race exertional heat illness in thoroughbred racehorses in temperate eastern Australia

“…The present investigation agrees with other epidemiological studies and has confirmed that post-race EHI occurs in the warmer weather between spring and autumn (Figure 1) in temperate eastern Australia. 1,3,4 In addition, it has defined the weather conditions under which EHI occurs. Among the individual weather elements, the strongest associations for post-race EHI are with VP (13.3%) and WS (4.6%) which, as outlined elsewhere, are the principal determinants of the evaporative capacity of the environment.…”

“…T here are many anecdotal and a few published reports of racehorses demonstrating erratic behaviours, becoming ataxic, collapsing and succumbing to a 'sunstroke-like' episode after competing in hot or humid weather conditions. 1 Although only recently described in detail in racing thoroughbreds, [1][2][3][4] Brownlow has provided detailed clinical descriptions of the characteristics of this syndrome and termed it exertional heat illness (EHI) after a similar condition in human athletes. 2,[5][6][7] There is, however, minimal literature on the rates of occurrence and environmental risk factors for this syndrome.…”

“…2,[5][6][7] There is, however, minimal literature on the rates of occurrence and environmental risk factors for this syndrome. [1][2][3][4] Thoroughbred racing in temperate eastern Australia occurs over relatively short distances and durations. The intense activity, however, can result in high rates of metabolic heat production and the potential for core temperature to become elevated to critical levels.…”