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 and a horse can overheat.
The University of Minnesota Extension recommends that you avoid riding altogether in hot and humid weather. If you must ride, ride in the early morning or late at night, and ride in the shade. In no event, however, should you ride when the combined temperature and humidity exceeds 150 – riding when the combined temperature and humidity is over 180 can be fatal to your horse.
The University of Minnesota prepared this chart showing the effect of heat and humidity on a horse’s ability to cool itself.
Boots or no boots?
If you do choose to ride, your choice of leg protection can affect your horse’s ability to keep itself cool during hot weather. 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 at the 2021 Equine Science Society’s virtual symposium.
The researchers explained that the bare limb is efficient and aerodynamic, in part because there are no muscles below the knee or the hock. 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:
1. A traditional neoprene boot;
2. A perforated neoprene boot;
3. A plant-based neoprene boot made of Stomatex;
4. A cross-country boot;
5. An elastic track bandage; and
6. A fleece polo wrap.
The study found that bare legs stay the coolest. 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.
The study presentation is available through until August 2 at https://www.equinescience.org/Meetings/2021-Meeting/Registration.
To scrape or not to scrape?
Industry organizations have issued conflicting advice on the best way to cool down a horse. In 2019, the FEI advised against scraping a horse after hosing with cold water, but other organizations continued to recommend scraping on the theory that it encouraged cooling through evaporation.
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 their results were counter-intuitive to many.
The researchers 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.
The study is available until August 2 at https://www.equinescience.org/Meetings/2021-Meeting/Registration.