Riding in Hot Weather: How Hot Is Too Hot, Signs of Heat Stress, and How to Cool a Horse

By Gayle Woods Editors Updated 5 min read

Horses produce a huge amount of heat when they work. Their big muscles burn energy, and the heat has to go somewhere. On a cool day, sweating and breathing take care of it easily. On a hot, humid day, they can't keep up, and a horse can overheat faster than many riders expect. Heat stress ranges from a tired, sluggish horse to a life-threatening emergency.

How horses cool themselves

Horses shed heat mainly by sweating. As sweat evaporates from the skin, it carries heat away. They also lose heat by breathing faster, and some through blood flow near the skin.

Humidity is the problem. In humid air, sweat doesn't evaporate well. It drips off without cooling the horse. That's why a 90°F day in the desert can be easier on a horse than an 85°F day with 80 percent humidity.

The temperature-plus-humidity rule

A simple rule many vets and extension services use: add the air temperature in degrees Fahrenheit to the relative humidity percentage.

Combined number What it means
Under 130 Horses cool themselves well. Normal work is fine.
130–150 Cooling is less efficient. Shorten rides, ease off, take more breaks, and cool carefully afterward.
Over 150 Horses struggle to cool themselves, especially if humidity is over 75%. Keep work light and short, or ride at a cooler time.
Over 180 Cooling barely works. Don't ride; focus on keeping horses cool.

Example: 85°F and 70 percent humidity add up to 155. That's a day for a short, easy ride early in the morning, not a long gallop at noon.

Direct sun, no breeze, a heavy coat, an unfit horse or a horse not used to heat all make things worse.

Signs of heat stress

Know your horse's normal temperature, pulse and breathing before summer. See horse vital signs.

Early signs:

  • Breathing stays fast, and the nostrils stay flared, more than 10 minutes after you stop
  • Heavy sweating, or sweating less than you'd expect
  • Lethargy, reluctance to go forward, stumbling
  • A high pulse that's slow to come down

Serious signs:

  • Rectal temperature over 103°F after work that doesn't drop with cooling. Over 105°F is an emergency.
  • Breathing rate higher than the heart rate, sometimes called an inversion
  • Dry, hot skin with little or no sweat
  • Dark, dry gums, slow capillary refill, a skin pinch that stays tented
  • Weakness, trembling, wobbling, collapse
  • A hiccup-like jerk in the flank, called thumps, from electrolyte loss

If you see serious signs, start cooling immediately and call your vet.

How to cool an overheated horse

Fast, aggressive cooling is the most important first aid for heat stress.

  1. Stop and get into the shade or a breezy spot. Untack.
  2. Pour cold water all over the horse, including the neck, chest, back, rump and legs, using a hose, buckets or sponges. Don't limit it to the legs.
  3. Scrape it off and pour more, or keep pouring continuously. Water that sits on a hot horse warms up quickly. Replacing it with fresh cold water keeps pulling heat away. A sweat scraper speeds this up.
  4. Keep air moving with a fan or by walking slowly between dousings.
  5. Check the temperature every five to ten minutes. Keep cooling until it's back under about 102°F and breathing has slowed.
  6. Offer water in small, frequent amounts. Let the horse drink.

The cold-water myth: an old belief says cold water on a hot horse's muscles causes cramping or tying up. Research done before major summer competitions showed that's not true. Cold water, even ice water, used generously, is the fastest and safest way to cool a hot horse.

Water, salt and electrolytes

  • Water: horses may drink 15 to 20 gallons or more a day in hot weather. Make sure clean water is always available, and check it often.
  • Salt: horses lose a lot of sodium in sweat. Feed about 2 to 4 tablespoons of loose salt a day in summer. Many horses don't lick enough from a salt block to keep up.
  • Electrolytes: for a horse sweating heavily during hard work, electrolytes replace sodium, chloride and potassium. Give them only with plenty of water available. A horse given electrolytes without water can become more dehydrated.

Helping horses adjust to heat

Horses adapt to hot weather over about two to three weeks. In early summer, or after shipping a horse to a hotter place:

  • Start with shorter, easier rides and build up.
  • Ride early or late in the day.
  • Give rest days.

Fit horses handle heat better than unfit ones, because their bodies produce and get rid of heat more efficiently.

Daily management in hot weather

  • Shade: trees or a run-in shed in every turnout.
  • Fans: a stall fan helps stalled horses cool off and keeps flies away.
  • Turnout timing: turn out at night and bring in during the hottest part of the day.
  • Clip heavy coats. Older horses with PPID that don't shed out properly suffer in the heat. Clipping them helps. See body clipping and senior horse care.
  • Sunscreen and fly masks for pink noses. See fly masks.
  • Trailering: haul in the cooler hours, open vents and windows, and never leave horses standing in a parked trailer in the sun. See hauling horses long distance.

Anhidrosis: horses that can't sweat

Some horses lose the ability to sweat, a condition called anhidrosis. It's most common in hot, humid climates, such as the Gulf Coast. Signs include a dry coat in hot weather, fast breathing, high temperature, and poor performance. Some horses sweat only under the mane or saddle.

Anhidrosis is serious, because the horse can't cool itself. Work with your vet on management: shade, fans, cool stalls, limited exercise in the heat, and sometimes moving the horse to a cooler climate.

Keeping yourself safe

Riders overheat too. Drink water before and during rides, wear a vented helmet and light, breathable clothing, and take breaks in the shade. A cooling shirt helps on the hottest days.

Sources

Frequently Asked Questions