Hotter, more-humid weather puts racehorses at risk of overheating while racing, and a horse with a history of overheating in hot, humid weather is more at risk of exertional heat illness, new research shows. A horse that overheats is susceptible to heat exhaustion and even death.
Scientists from the University of Bristol recommend that racing officials monitor the wet bulb globe temperature index to help decide if racing should continue. This index is based on temperature, humidity, wind speed, and solar radiation.
Warming temperatures mean that more race days are becoming hotter than in the past, so racing officials in places like Australia and Japan have investigated what factors can lead to heat illness in horses. Thus far, there has been no conclusive way to predict which racehorses may overheat.
Dr. Leah Trigg, from the University of Bristol's vet school, worked with the British Horseracing Authority and University College Dublin to examine data on 704,434 racehorses on British tracks that were recorded in the BHA database between July 2010 and April 2018.
In total, 702 episodes of exertional heat stress or heat exhaustion were recorded during that time, equating to 0.1 percent of the horses.
The scientist modeled the probability that a racehorse would experience heat stress or heat exhaustion (collectively called heat illness) if the horse had a previous heat health incident, race distance, race start time, footing conditions, average temperatures in the five days before the races, and wet bulb globe temperature index.
In total, the model predicted 83.5 percent of exertional heat illness events, though the researchers noted that the model may produce a high number of false positives.
Predictive factors included longer race distances and higher wet bulb globe temperature indices. Horses that have overheated before were 18.59 times more likely to overheat again. Running on heavy or soft ground, or in races before 5 p.m., also increased risk of overheating.
Higher temperatures in the days leading up to the race were associated with reduced risk of overheating, the team concluded. This suggests that racehorses may acclimate to warmer temperatures.
Trigg suggests track officials monitor the wet bulb globe temperature index at race meets to determine whether racing should continue or if additional cooling areas should be provided. She recommends that this data be used to create evidence-based policies to protect racehorse welfare.
Read more at HorseTalk.
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