Handling The Heat: Racetrack Policy And Running During The Dog Days Of Summer by Sarah Coleman|09.03.201505.18.2022|4:40pm3:42pm While heat and humidity are still going strong in most areas of the United States, racetrack officials and veterinarians must decide at what point temperatures become too hot for horses and their jockeys to run races safely. But how is this determined? And what happens if horses are asked to run in unsafe temperatures? What Happens To Horses In The Heat? “As a mammal, a horse needs to maintain its core temperature as close to normal as possible,” said Dr. Fernanda Camargo, DMV, PhD, equine extension professor at the University of Kentucky. The reason high temperatures and humidity become a concern is that the horse needs to be prevented from overheating. “When horses are asked to perform strenuous exercises, their working muscles generate heat. Heat needs to be dissipated in the form of sweat so the body doesn't overheat,” she said. The sweat then evaporates and the horse is able to maintain a normal body temperature. “Sweat accounts for 70 percent of heat dissipation,” said Camargo, which is why she said easy to see why high humidity—and no wind–would compromise a horse's ability to cool itself. “Horses can also pant, and that accounts for about 15 percent of heat dissipation. The idea is that they exhale hot air and inhale in cooler air, and thus help to diminish the body temperature.” A hot horse will also have vasodilation, where their veins open and blood is carried from the hot muscles to the skin so the air will help cool the blood. “Horse are big, and therefore produce a lot of heat that needs to be dissipated. If you think of all the working muscles, plus the enormous GI tract [digestion also produces heat], you can imagine how hard the mechanism needs to work to maintain normalcy,” said Camargo. When both heat and humidity are high, the horse cannot cool himself down as easily; sweat will not evaporate and the hot air will not cool the blood brought to the skin. What Happens If The Horse Can't Cool Down? “In general, a horse's body temperature, heart rate and respiratory rate should return to close to normal within 30 minutes after exercise,” said Camargo. If that is not the case, the horse may be experiencing heat exhaustion or even heat stroke. This means that more than one organ system might stop functioning properly, such as the muscles, kidneys or central nervous system. Without prompt intervention, the horse might suffer irreversible damage. “When the horse's body temperature has reached 105 degrees Fahrenheit, the blood supply to the muscles will begin to shut down. Thereafter, the blood supply to the intestines and kidneys will also shut down. The brain and heart are the last ones, but severe and permanent damage may have already taken place,” said Camargo. How Do Tracks Prevent This? Because of these severe consequences to horses overheating, many tracks are diligent about monitoring both the heat index and how horses are coping with the weather. Temperature becomes an issue primarily when coupled with high humidity, which raises the ambient temperature significantly. Track officials use a heat index calculator to determine how hot it really feels when relative humidity is factored in to the actual air temperature. To determine the index using Fahrenheit, the temperature and the humidity percentage are added together, then the wind speed is subtracted. “This is because wind improves heat loss from evaporation, and convection,” said Dr. Rick Arthur, DVM equine medical director for the California Horse Racing Board. “When you get around 160 [combined heat and humidity], it becomes a bit problematic. Some vets advocate that rather than 180 [the number most tracks use to determine horse and jockey safety], that 170 would be a better number.” With this heat/humidity index, track officials are “trying to determine the horse's ability to lose heat,” said Arthur. “Once it gets over 130, they [the horses] become compromised.” There's also no substitute for just keeping trained eyes on horses to see how the individuals are experiencing the environment. “Horses at Gulfstream and Gulfstream Park West are monitored throughout the day,” said a track spokesman for Gulfstream. “Our veterinarians check on horses running each morning, as they walk up for their respective races, and during saddling, post parade and gallop out.” In an effort to keep horses as cool as possible, “water hoses are placed strategically throughout the track, saddling enclosure, walking ring and winner's circle,” said Joseph. “You will also see grooms, assistant trainers and trainers with water buckets when horses come back after a race.” Other ways horses are encouraged to cool out rapidly back at the barn include hosing them with cold water and scraping off the excess water, using rubbing alcohol to evaporate and dissipate the heat, and standing the horses in front of fans. At Gulfstream and Gulfstream Park West, the track veterinarians ultimately decide whether or not it is too hot for the horses to run and management reported it will always abide by the decisions of the vets.