Risk factors for, and prediction of, exertional heat illness in Thoroughbred racehorses at British racecourses

Abstract

The development of exertional heat illness (EHI) is a health, welfare and performance concern for racehorses. However, there has been limited multivariable assessment of the possible risk factors for EHI in racehorses, despite such information being vital for regulators to effectively manage the condition. Consequently, this study aimed to identify the risk factors associated with the occurrence of EHI in Thoroughbred racehorses and assess the ability of the risk factor model to predict the occurrence of EHI in racehorses to assist in early identification. Runners at British racecourses recorded in the British Horseracing Authority database between 1st July 2010 and 30th April 2018 were used to model the probability that a horse would present with EHI as a function of a suite of environmental, horse level and race level factors. EHI was reported in 0.1% of runners. Race distance, wet bulb globe temperature, preceding 5-day temperature average, occurrence of a previous EHI incident, going, year and race off time were identified as risk factors for EHI. The model performed better than chance in classifying incidents with a mean area under the receiver operating characteristic curve score of 0.884 (SD = 0.02) but had a large number of false positives. The results provide vital evidence for industry on the need to provide appropriate cool down facilities, identify horses that have repeated EHI incidents for early intervention, and collect new data streams such as on course wet bulb globe temperature measurements. The results are especially relevant as the sport is operating in a changing climate and must mitigate against more extreme and longer spells of hot weather.

Effect of a 14-Day Period of Heat Acclimation on Horses Using Heated Indoor Arenas in Preparation for Tokyo Olympic Games

“…Nevertheless, to ascertain the applicability of laboratory-based acclimation studies in real-world scenarios, conducting the current study is of paramount importance. As fitness, age, and breed have significant effects on the physiological responses to heat [11,12], it is necessary to investigate whether Warmblood sport horses respond in a similar manner to heat acclimation. In addition, the authors of this study chose elite horses for several reasons: (1) high-level competition horses are transported across the globe to participate at international events, challenged with sudden large climate changes to cope with, (2) Warmblood sport horses may respond differently compared to research horses, (3) these specific Warmblood horses were highly fit for competition and may respond differently than less fit or lower-level horses, and (4) it is not likely that high-level competition horses will prepare for thermally challenging climates by using treadmill exercise due to the fact that they are not used to this type of exercise, and that in itself may increase the risk of injuries when suddenly induced for 1 h a day for 14 days.…”

“…Adding to this, as a result of the evidence of a changing climate, an increasing number of horses will face challenging thermal conditions when being exercised or housed. As shown by Takahashi et al [11] and Trigg et al [12], exercising in hot conditions increases the risk of heat-related illnesses in horses. Therefore, it is crucial to gain a better understanding of methods that can be employed to help horses alleviate thermal strain when performing in thermally challenging climates.…”

Thermoregulation during Field Exercise in Horses Using Skin Temperature Monitoring

“…The prevalence of metabolic disorders in endurance horses ranges from 2% to 15% [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. In comparison, for maximal intensity exercise, EHI screening studies have recently reported a prevalence between 0.1% and 1.1% in racehorses in Australia, the UK, and Japan [ 15 , 16 , 17 , 18 , 19 ]. A study in eastern Australia focused on selected EHI cases post-exercise at the racetrack and suggested an EHI incidence of up to 9.5% during hot summer months [ 17 ].…”