Beat the Heat
Horses have efficient natural thermoregulatory systems to cool themselves, but sometimes they are overwhelmed and cannot compensate for the heat. Hyperthermia or heatstroke results when a horse is unable to control its internal temperature and it starts to rise.
Signs of heatstroke are an elevated respiratory rate—40-50 breaths per minute (normal: eight to 16)—that does not slow when at rest; a heart rate more than 80 beats per minute (normal: 36-44 beats per minute) that does not slow down after a few minutes of rest; elevated rectal temperature more than 103°F (normal: 99-100.5°F); lethargy; and/or profuse sweating or absence of sweating altogether. If left untreated, hyperthermia can cause death. Neither the heat alone nor the humidity alone is concerning, but the two factored together is. Most researchers define high heat as more than 86°F and high humidity as 80-85%.
Hyperthermia can occur when one of these three things is present: inadequate (fitness) conditioning, extreme hot and humid conditions, or a weakened thermoregulatory system.
Careful management can help your horses keep their cool.
Assess conditioning: Evaluate your horse’s current physical condition and body condition score. Most obese horses or poorly muscled, thin horses cannot combat the extra stress of working in the heat. If your horse has not been in regular work or you are unsure about a new horse’s work history, begin your summer workouts slowly. Increase duration and intensity slowly to give the horse time to acclimate to the heat and humidity.
Replace electrolytes: Give your horse electrolytes in a water bucket or in feed. The horse loses salt and other minerals when it sweats, and these must be replaced. When adding electrolytes to water, make sure you also have a water bucket available without electrolytes. The horse might not like the taste of the electrolytes or might not need many electrolytes.
Cool the horse properly: After you work in the heat, apply cool water to your entire horse. Spend time hosing the largest muscle areas and the largest and closest-to-the-surface blood vessels—the jugular vein in the neck and the saphenous vein on the inner thigh. Doing this cools the body faster. Install a fan if your horse sweats while standing in the stall; some of these fans include water misting systems.
If the horse develops hyperthermia:
• Stop activity immediately and remove the saddle;
• Hose your horse with the coldest water available or a water/alcohol mix. Scrape the used water off and repeat;
• Offer your horse water and allow him to drink;
• Move your horse to the shade or a breezy location; and
• Call your veterinarian.
The earlier you recognize the signs of hyperthermia, the earlier the veterinarian can begin treatment and prevent further damage. Acclimating to heat and humidity does not guarantee that your horse will not get hyperthermia, so always keep an eye on your horse’s health when training in the summer.