Do Horses Sweat? Prevent Heat Stress in Horses
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Do horses sweat? Learn tips for preventing equine heat stroke symptoms and how horses release body heat.
by Heather Smith Thomas
Heat stress is a dangerous condition that can occur when horses are overworked in hot weather. Extremely hot, humid weather can pose a risk by itself, but this condition is more likely to be life threatening when a horse is exerting itself (creating more body heat) or hauled in an enclosed trailer with inadequate ventilation. There’s a difference between a horse that’s just hot (suffering from heat stress) and a horse that has collapsed — with a body temperature of 108 to 109 degrees Fahrenheit (heat stroke) — and is about to die.
The danger can be minimized by proper care and conditioning. Everyone who works with horses should know the signs of trouble, and be aware of subtle changes. You need to pay attention to symptoms, stop working the animal, and reverse the condition before its too late.
Do Horses Sweat?
Horses draw in more air during exercise to bring extra oxygen for working muscles, but also to dissipate heat. They flare their nostrils to pull cooler air to the large inner surface of the lungs and blow the hot air back out.
How the Body Dissipates Heat
It’s extremely important for a horse to sweat. A few horses don’t sweat much, or sweat in patches, which makes them more prone to overheating. When sweat evaporates from the body surface, it cools. If a horse has to sweat continuously, however, it can lose too much fluid and dehydrates.
When a horse gets too hot, they want to stop working, and this is something anyone working with a horse should pay attention to. Even if a horse tends to be lazy, if they want to stop, consider the possibility that they may need to stop.
The normal temperature for a horse can be 99 to 101 degrees F, depending on the individual. Core temperature (where heat accumulates inside the body) is what’s important. A rectal temperature may be a little lower than the actual core temperature.
Conditions that Lead to Heat Exhaustion/Heat Stroke
There’s a point at which the horse starts overheating, when their cooling systems aren’t working fast enough to keep up with accumulation of heat. If their temperature continues to climb and gets into the 106- to 107-degree F range, it can’t stay there long or the condition becomes deadly.
Factors that increase risk include high humidity during hot weather. When air is full of moisture, evaporation slows or ceases; sweat loses its cooling effect. If air is dry, there’s a swift cooling; sweat comes out hot, dissipates into the air taking heat with it, and cools the body surface. If it can’t evaporate because the air is already full of moisture, it sits on the skin, hot. It holds the heat in, rather than dissipating it. The body doesn’t cool, and signals for more sweating. Sweat may run off in streams because it can’t evaporate. The horse stays wet but doesn’t become cooler. If they continue to work, they quickly dehydrate and overheat.
In an arid climate, sweat evaporates almost as fast as it is produced, constantly cooling the body. If you put water on a horse to help them cool off, it evaporates. But on a hot humid day, the moisture just sits there; you have to scrape it off to take any heat with it. You put cool water on, take the warm water off; then put more cool water on.
If the air is dry and there’s a little breeze, sweat evaporates so fast you don’t even see the sweat. This is an ideal situation, because the horse will cool very well.
Be aware of weather conditions, especially the heat index. Don’t work a horse hard when temperature and relative humidity together are dangerously high. A rule of thumb: when temperature and humidity numbers are added together and the total exceeds 130 (such as 80 degrees F with 50 percent humidity) there is risk of overheating. If the total gets to 150 or higher, this is the danger zone; a working horse will likely overheat.
If the temperature is 90 degrees F the horse may get in trouble even if humidity is only 40 to 50%. They may also be in trouble if it’s only 75 degrees F and humidity is 75 percent. When humidity is high, horses can overheat at a lower temperature because they can’t get rid of the sweat and are unable to cool themselves.
Another factor is body mass. Large, overweight, and heavily-muscled horses and heavily-pregnant mares don’t dissipate heat as well as small, lean horses. Quarter horses, draft horses, or any big heavy horse overheats faster than a trim, well-conditioned Arabian, for instance. A big horse may overheat since it’s a long way from the middle of the body to the outside. Heat must dissipate from the body core, either through the lungs or skin. The more bulk, the more potential problems.
Signs of Heat Stress/Dehydration
If the body is trying to regulate temperature by sweating and breathing faster but can’t keep pace with heat accumulation, the horse becomes weak and “exhausted.”
Dehydration from excess sweating complicates the process of temperature regulation. Important salts have been lost with the sweat, creating critical changes in the electrolyte balance of the body. This can interfere with nerve signals (since electrolytes are crucial for proper nerve and muscle function). Erratic nerve signals contribute to digestive tract malfunction, irregular heartbeat, muscle cramps, etc. Some horses develop “thumps” (the abdomen jerks each time the heart beats).
Unbalanced electrolytes cause other problems, too. Skin becomes less elastic due to fluid loss from underlying tissues. A pinch of skin pulled out from the neck or shoulder doesn’t spring back into place but stays tented a few seconds. If it takes 2 or 3 seconds for the skin to sink back, the horse is moderately dehydrated (has lost about 4 gallons of fluid — equivalent of 32 pounds of body weight). If the pinch of skin stays elevated 6 seconds or longer, they are severely dehydrated. Knowing how your horse responds under ideal conditions will help determine how well this test applies.
Mucous membranes in the mouth (such as the gums) become dry and discolored, turning brick red instead of “bubble gum pink.” Heart rate increases as the body tries to pump more blood to the surface for cooling, but has less fluid to do it. The horse’s eyes seem sunken; eyelids and tissues around the eyes look wrinkled, due to loss of fluid in the tissues. Sweat is thick and sticky instead of clear and watery. Capillary refill time is longer than normal; if you press your finger into their gum, blood does not rush right back. That spot where you pressed out the blood stays pale for several seconds.
Pulse and respiration rate may remain high in spite of rest. Pulse may be weak, heart rhythm may be irregular, intestinal sounds diminished or absent (the gut stops working) and muscles of the anus may become relaxed and floppy; the anus sags open.
The horse will be depressed, with little interest in eating or drinking. If a tired horse will eat, this is always a good sign. Green grass is the best food for a tired, dehydrated horse. Do not feed grain.
If you stop working the horse at first signs, and let them cool out and drink, the condition won’t progress to heat exhaustion or heat stroke. Check your horse’s pulse and respiration periodically during and after a workout. Take their temperature to see how overheated they are and how quickly they recover.
Equine Heat Stroke Symptoms
- Signs of heat stroke may begin as sudden, unexpected fatigue. The horse can’t keep going, and stumbles.
- Pulse, temperature, and respiration rate are elevated.
- They may become anxious, behaving in an irrational or erratic manner, due to overheating of the brain.
- They may be excited, depressed, or disoriented.
- Rectal temperature may rise as high as 106 to 110 degrees F.
- Skin will be hot and dry, since they have run out of fluid for sweating.
- They may be oblivious to their surroundings, and have difficulty moving.
Unless the condition is quickly reversed, they will collapse, go into convulsions or coma, and die.
Dealing With a Too-Hot Horse
If the horse is only mildly overheated, halt and remove the saddle (or harness) and sponge them with water, especially over major blood vessels, and provide shade. Walk them in a big circle if there’s a breeze, to cool them on all sides. Once they seem cool, check pulse, respiration, and temperature again 15 minutes later, and again 30 minutes after that. If they’re not completely cooled (temperature still elevated, body retaining internal heat), they may break out in a sweat again. If that happens, walk and cool them again. After strenuous work in hot weather, check them again several hours after you’ve cooled them, since some horses may be at risk for colic or laminitis after working in the heat.
If the horse is severely overheated, call a veterinarian; the horse needs large volumes of IV fluids to restore what’s been lost and restore proper circulation. While waiting for the vet to arrive, try to lower their temperature. Keep air moving around them with fans, or manual fanning. Apply cool water over areas where major blood vessels are close to the body surface — such as jugular groove and the big blood vessels on the belly.
This is more beneficial than putting water over the whole horse. If you chill the big muscles, they contract and constrict the blood vessels, hindering dissipation of heat. If humidity is high, you can pour cool water over their big muscles, because it’s not evaporating fast. In an arid climate, however, this might make the muscles cramp up.
In humid conditions, keep applying cool water all over the horse and scraping it off, since the water warms up immediately once it’s on the horse. Scrape off the warm water and apply more cool water. Periodically walk the horse briefly. Keep alternating walking and cooling, since moving helps promote blood flow to skin, and air movement aids evaporation (unless the humidity is too high). Keep checking their temperature. It should drop about 2 degrees within 10 minutes. Once it starts to drop, slow down on the cooling. Stop using cool water as soon as their temperature comes down to 101 degrees F, or when the skin over their hindquarters feels cool after a walking period, or when respiration rate drops below 30. Stop if the horse starts to shiver.
Don’t use ice packs over the muscles, since this constricts surface blood vessels and hinders blood flow to the skin, which slows the cooling process. If you use wet towels over the neck or head, continually pour cool water on them. A wet towel left in place without adding cool water will soon warm up and act as insulation, retaining heat.
The legs have a lot of exposed blood vessels. There’s not much muscle over those vessels. Wetting the legs with cool water, including the feet, can help cool an overheated horse. If there’s a stream nearby, walk the horse into it. Stand them in water while you apply water to keep their jugular vein and abdominal veins wet. Keeping their feet cool will also help reduce the chance of founder.
HEATHER SMITH THOMAS ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history. She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Find Heather online here.
Originally published in the July/August 2024 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.
