EQUINE
JULY 27, 2023 | THE WELLINGTON ADVERTISER | 17
Heat stress and dehydration can harm horses: OVC professor By Robin George GUELPH – Dripping with sweat and breathing hard through flared nostrils, an agitated horse shakes her head. The horse stumbles, ears pinned back, and kicks out. During this summer of high temperatures it’s important to recognize and respond to symptoms of heat stress. If left untreated severe heat stress can be fatal, said University of Guelph Ontario Veterinary College (OVC) assistant professor Amy Lack. She completed her veterinary training in Missouri, and then completed a residency in equine internal medicine in the southern U.S., so she’s no stranger to handling horses’ health in hot weather. Severe heat stress is relatively uncommon, Lack said, because most owners are quick to notice and respond to problems. Recognizing heat stress “Just like you and I, horses experience heat stress,” Lack said. “The difference is, when we start feeling the impact of the heat, we take a break.” Because horses work in partnership and enjoy exercise, they often push past their capacity. So it’s up to people to recognize signs of heat stress and dehydration. In early stages heat stress can cause depression, lethargy, heavy breathing and dilated nostrils, Lack said. As heat stress progresses it impacts how cells communicate and proteins function, sometimes leading to brain dysfunction, she added. An overheating horse may become unsteady or irritated. Horses that are usually easy-going may rear or strike
out, becoming dangerous to handle. A horse experiencing severe heat stress may become “completely unaware of what’s going on around them,” Lack said. They may collapse, or throw themselves on the ground, and without intervention they “could have a seizure, become comatose, or potentially die.” Wet-bulb globe temperature To avoid potential heat stress, Lack recommends being mindful of the wet-bulb globe temperature (WBGT) – a measurement including air temperature, humidity, wind and solar radiation. Lack said the heat index, measuring air temperature and humidity, is a good representation of conditions in the shade, but WBGT is more accurate for sunny conditions. If the WBGT exceeds 33, Lack recommends not exercising horses at all. When the WBGT is between 30 and 33, moderate exercise is safe, but Lack advises taking precautions: - exercise horses early in the morning when it’s coolest; - stick to grassy surfaces instead of sandy arenas as grass is cooler; - take frequent water breaks in the shade; and - look out for signs of heat stress and dehydration. Some horses have higher heat tolerance than others; a well conditioned horse will have an easier time exercising in hot weather than one used to spending most of their time grazing in the field. And a horse unaccustomed to hot weather will overheat more easily. When Ontario weather warms
It’s important to protect horses from heat stress and dehydration during hot weather, says Ontario Vetinary College assistant professor of large animal internal medicine Amy Lack. Photo by Robin George quickly in March, Lack said it takes horses at least five days to acclimate to the new temperature. Responding to heat stress When something doesn’t seem right while exercising a horse, the first step is to stop. “If you have any concern a horse is not okay, it’s best to touch base with a veterinarian,” Lack said. Even if the vet doesn’t need to see and treat the horse, they can offer guidance and keep the horse on their radar in case things take a turn for the worse, she added.
“If you suspect a horse is experiencing heat stress, move them to a cool place and start hosing them down with cool water,” Lack said. Spray the underside of their neck, where the jugular veins are, as this will cool their blood most rapidly. The horse’s body temperature will quickly warm the water, which should be scraped off with a sweat scraper. Lack recommends spraying and scraping the horse until they seem less distressed and their skin feels cool. Hydration Sweating is the primary way horses
control their body temperature. “Horses are phenomenal sweaters,” Lack said. “Probably the best sweaters in the mammalian world” – they can produce over 10 litres of sweat in less than an hour. Their impressive ability to sweat is part of what makes them such great athletes, Lack said. It also makes hydration essential. Dehydrated horses use water reserves from their gastrointestinal system to make sweat.
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