–Originally published in the August 2025 issue–
At the time of this writing we are still in July, and the weather this July has been brutal. We have had several weeks of high heat and high humidity, and the humidity has not eased even in the wee hours of the night.
This poses significant health risks for our horses.
Horses evolved in colder, drier climates, and they can struggle to keep their body temperatures cool in our Maryland summers. A high internal body temperature, if it continues for too long, can lead to heat stroke, brain injury, or death.
Horses normally cool themselves by sweating. The evaporating sweat creates a cooling effect. When the humidity is high, however, sweat does not evaporate as quickly and a horse can overheat.
While the best thing for your horse is to avoid riding at all in very hot, very humid weather, if you must ride, ride in the shade during the time of day when the humidity is the lowest. In Maryland, the least humid time of the day is often around 4 p.m.—after the humidity of the morning has dissipated and before the humidity of late afternoon thunderstorms has developed. Most weather apps can tell you when during the day the humidity will be lowest.
Your horse’s ability to cool itself is at its best when the combined temperature and humidity is less than 130. It is decreased when that number is between 130 and 150, and greatly reduced above 150. When the efficiency rating is above 150, the best expert advice is to avoid any strenuous work and to avoid riding in the sun. Think leisurely trail rides in the woods, not jump schooling or conditioning in the sun. Riding when the combined temperature and humidity is above 180 can be fatal.
As a practical matter, this means that conditions can be dangerous for your horse even when the temperature is below 90°. A 75° day with 75% humidity is enough to get you to danger zone of 150. Schooling or conditioning when it is 95° out with 85% humidity could be fatal for your horse.
Below is an equine cooling efficiency chart to help.
Boots or no boots?
If you do choose to ride (hopefully in the shade), your choice of leg protection can also affect your horse’s health. A study by Middle Tennessee State University looked at how boots and leg wraps increase leg temperature, and the extent to which the increased leg temperature risks tendon injury. The study was presented the 2021 Equine Science Society’s virtual symposium.
The researchers found that while the bare limb is efficient and aerodynamic, boots and bandages insulate the legs and raise the limb’s internal temperature above baseline. Heat can damage the superficial digital flexor tendon. The digital flexor tendon has a higher core temperature than skin anyway, and it is hypo-vascular, so it loses very little heat in the bloodstream.
The researchers studied six different types of boots: (i) a traditional neoprene boot; (ii) a perforated neoprene boot; (iii) a plant-based neoprene boot made of Stomatex; (iv) a cross-country boot; (v) an elastic track bandage; and (vi) a fleece polo wrap. The study found that none of the limbs wearing leg protection returned to base line temperature within the 180-minute recovery period, and “the hyperthermic effect of [all] boots and bandages” was enough to “cause chronic microdamage to the tendon.” The most damaging leg wraps for hot weather exercise were the fleece polo wraps.
To scrape or not to scrape?
If you have chosen to ride in this weather (hopefully in the shade without boots!) you should keep in mind the latest science on how to cool your horse down quickly.
In 2019, the FEI advised against scraping a horse after hosing with cold water. Also in 2019, researchers at University of Queensland’s School of Agriculture and Food Sciences studied three different methods for cooling a horse after exercise, and they found “no cooling effect of scraping following rapid cold-water application.” The cold water started cooling the horse’s internal temperature immediately, but the moment the water was scraped off, the cooling effect stopped and the horse’s internal temperature began to rise again.
Researchers saw the biggest cooling effect in horses that were bathed in 8 gallons of cold water every minute, for 5 minutes, without scraping.
What does that mean for us? Get out your hose, set your timer for 5 minutes, and when the time is up, leave your horse dripping wet and give her the rest of the day off.
– Kimberly K. Egan is the Vice President for Publications
