This horse’s panting and flared nostrils indicate efforts to cool down overheated muscles. Cool air (and oxygen) is exchanged for warm, exhaled air.

It’s a glorious summer day. Your horse’s hooves tap out the beat of the trail as you trot along, the stillness of the day punctuated by an occasional puff of wind ruffling the leaves. Beneath your helmet, your head feels hot and sweat drips off your face. Your horse’s neck is soaked, your reins slippery and lathered.

But suddenly, the more effort you ask of your horse, the lazier he seems. It feels as though he’s mired in deep footing, the ground holding him down. In fact, he’s run out of steam, or rather, his body is boiling over with too much heat. He’s nearing a dangerous state of exhaustion. You pull him up, yet his muscles remain quivering, his breaths come quickly, and his nostrils are flared. Could you have foreseen this development? Could you have prevented your horse from pushing the red line into the hot zone?

Although most trail rides don’t require extreme exertion bordering on catastrophe, heat and humidity conditions or taxing terrain may push your horse beyond his ability to cool down on his own. And all horses will need some assistance with cooling in the summer.

Here, we’ll explain how heat builds up (and what you can do to prevent it) and how to check for signs of heat stress. Then we’ll give you several cooling techniques. We’ll also outline two heat-related conditions and tell you how you can keep cool on hot days. 

Heat & Your Horse
Below are six ways your horse can become overheated, and what to do to help him stay cool.

When you ask your horse to exert his muscles, especially uphill.

Hot weather. Hot weather, particularly if it’s also humid, makes it harder for your horse to shed heat from his body.

What you can do: In summer months, head out in the early morning hours; allow your horse to stand idle during the heat of the day. Offer him plenty of water. Use less body-covering tack than usual to expose as much of his skin as possible to cooling airflow. 

Overexertion. Heat is a byproduct of muscle exertion. As your horse’s muscles push him forward, they contract and strain with the effort of each stride. Over half of the energy used in muscle exertion is converted to heat. If you ride your horse at too fast a speed for his level of condition, he’ll overheat, stimulating a decline towards exhaustion and muscle fatigue. Loss of muscular control and strength can lead to accidents; a tired horse may stumble and fall, placing both horse and rider in jeopardy.

What you can do: Avoid pushing your horse too hard. If you plan to go on a strenuous trail ride (especially one involving hills), first condition your horse. On hard rides, allow him to take frequent breaks in the shade, preferably at a stream or other water source. Cool him with water soaks of the head, neck, legs, and chest. During breaks and after your ride, immediately loosen or remove the saddle.

He’ll sweat to cool down

Dehydration. Your horse sweats to remove heat generated by working muscles. When he sweats, he pulls heat from his body in a process known as evaporative cooling. In doing so, he loses body fluid and electrolytes (minerals essential to his body’s chemical processes). If you ask too much of your horse for too long, he’ll become dehydrated as he sweats to cool himself. Even a well‑conditioned horse loses as much as two to three gallons per hour exercising in high heat and humidity.

What you can do: Follow the tips for avoiding overexertion, above. Offer water frequently. Encourage your horse to drink unfamiliar water by flavoring it with apple juice. Give him a dose of electrolytes ahead of your ride, and make sure he always has water available.

Your horse’s gum color and capillary refill time indicate how well he’s circulating blood — a sign of heat recovery.

Excess weight. An overweight horse with abundant fat layers beneath his skin can’t dissipate heat effectively. Not only does excess body weight interfere with normal cooling processes, but it also reflects a lack of fitness. Conditioning expands capillary beds and blood flow to improve circulation of oxygen and to flush heat to the skin’s surface.

What you can do: With the help of your veterinarian, help your overweight horse become fit and lean by increasing exercise and moderating caloric intake.

Signs of heat stress include a grumpy disposition, lack of alertness, dull or glazed eyes, wrinkled lips, and ears at half-mast.

Haircoat. Naturally, your horse’s winter haircoat keeps heat in.

What you can do: If an early spring warm up collides with your horse’s winter coat, clip him. Pay particular attention to the neck, chest, and underbelly, where large blood vessels bring heat to the surface.

Trailering. Transporting your horse in an enclosed trailer in hot weather also contributes to dehydration and heat stress.

What you can do: Open screened windows and ceiling vents to maximize airflow. Offer water at frequent rest stops on the road and after you arrive at your destination. When possible, haul in a trailer with an insulated ceiling.

If you ask too much of your horse for too long, he’ll become dehydrated as he sweats to cool himself. He’ll also lose electrolytes.

Signs of Heat Stress
Your horse’s external signs of heat stress may range from subtle to obvious. If he exhibits any of the following signs, stop, and cool him down immediately. (See “Cooling Techniques” on page 83.) If he still doesn’t seem to recover, call your veterinarian immediately.

General condition: Flagging body posture; lethargy; seems weak and/or uncoordinated; stride flattens out; poor impulsion or stumbling; sagging or deflated posture when pulled to a stop.

Mood: Grumpy disposition when handled and/or when asked to perform; lack of alertness or interest.

Facial signs: Dull or glazed eyes; wrinkled lips; ears at half-mast; anxious expression.

Body processes: Waning or absence of appetite; lack of thirst; reduced or absence of urine; reduced or absence of manure.

Heat-related conditions: Myositis (tying-up syndrome); thumps. (For more information, see opposite page.)

Your horse’s vital signs will also tell you how well he’s coping with the heat. These include heart rate (or pulse), respiration, gum color/capillary refill time, hydration level, and body temperature. Here’s a rundown of each one. 

Heart rate (pulse). Your horse’s pulse, or heart rate (measured in beats per minute), will tell you how well he’s recovering from exercise. His pulse should return to normal, post-exercise range — about 60 to 64 beats per minute — within 10 minutes.

How to monitor: Place a stethoscope just behind your horse’s left elbow, or a finger on the bottom of your horse’s jaw line, on the large artery you’ll find there. Count beats per minute for 15 seconds, then multiply by four.

Respiration. Your horse’s respiration (measured in breaths per minute) also tells you how well he’s recovering. Like his heart rate, his respiration should return to a normal post-exercise range — 12 to 24 breaths per minute — within 10 minutes.

How to monitor: Simply count your horse’s breaths for 15 seconds and multiply by four. 

Gum color/capillary refill time. A careful peek at your horse’s gum color and normal capillary refill time indicates how well your horse is circulating blood through his body, which is another sign of recovery.

How to monitor: To check gum color, gently lift your horse’s upper lip; his gums should be a healthy pink, like the pink beneath the nail of your pinky finger. A dark red or purple color can indicate shock. To check capillary refill time, blanch his gums with a fingertip; the pink color should return within two seconds.

Heat-Related Conditions

Here are two heat-related conditions to watch for on the trail.  Myositis. This condition, a type of muscle inflammation, is also known as tying-up syndrome, exertional rhabdomyolysis, and azoturia. Your trail horse’s muscles may cramp due to heat stress, dehydration, electrolyte imbalances, and/or energy depletion.   Signs of myositis: Typically, you’ll see a muscle cramp, similar to a charley horse in your leg. Your horse might stop dead in its tracks and refuse to move. If you feel his haunches or thighs, you might find a very firm muscle group that’s painful to touch. However, the signs can be more subtle. Your horse may only shorten his stride, or one rear leg may look slightly “off.” His attitude may turn grumpy. He may flag in his effort, or want only to walk or slow trot. If the problem isn’t obvious at a walk, then have a helper trot your horse away from you on a straight line to see if there’s any lameness or a shortened stride.  Your horse’s inflamed muscles may also release myoglobin, a large protein molecule. Once released, it passes through the kidneys where it can cause a blockage, leading to kidney failure. An external sign of myoglobin release is red-tinged or brown urine. If you were to press forward, your horse’s muscles can undergo further and potentially significant damage. Some horses act colicky, sweat, and throw themselves on the ground. Others show poor heart-rate recoveries and gait irregularities.  What you should do: If you spot any signs of myositis, dismount, send someone on to get your trailer, and bring your horse home or to your veterinarian. While you wait, stand quietly to the side of the trail, and offer water, if available. If you’re on the trail with no other rider to help you, slowly walk your horse home or to the trailer, taking frequent rest breaks. If symptoms persist, call your veterinarian immediately.

Dehydration. Dehydration notably slows heart-rate recovery and is another sign of heat stress.

How to monitor: To roughly estimate dehydration level, grab a fold of skin on your horse’s point of shoulder or an eyelid; it should snap back into position immediately. If the skin remains “tented” (refuses to return to its normal position), your horse may be seriously dehydrated. Signs of mild dehydration are a dry mouth and mucous membranes. At the next stage, the eye sockets appear sunken in, skin elasticity is markedly reduced, and your horse appears weak, with a dull or listless attitude and posture.

Rectal temperature. On the trail, your horse’s normal rectal temperature ranges from 101 to 103 degrees Fahrenheit. If his temperature exceeds 103.5 degrees F, he’s considered overheated. Once you stop for a rest, his rectal temperature should decline steadily over 15 to 20 minutes. (Help him cool down by soaking his neck, chest, and legs with water.) A rectal temperature exceeding 105 degrees poses a dangerous situation, requiring immediate and aggressive cooling measures. At 106 degrees, he can suffer kidney, liver, and brain damage. At temperatures greater than 107 degrees, he may go into convulsions or coma, and die.

How to monitor: Use a glass or digital rectal thermometer designed for equine use (available at tack stores, through veterinary-supply catalogs, and online). Shake down a glass thermometer, or activate a digital one. Apply a dab of lubricant, such as K-Y or petroleum jelly, to its tip. Slide the tip of the thermometer into your horse’s anus to a depth of about two inches. Wait about two minutes for a glass thermometer, or 30 seconds for a digital one (you’ll hear a beep). Remove, wipe, and check the reading.

Cooling Techniques
Before your horse exhibits signs of heat stress, you can ward off mounting heat in his muscles with the following techniques.

Walk your horse. At intervals along the trail, bring your horse to a walk. Hop off, remove the saddle, and walk him for a minute or two so blood flow continues to flush metabolic waste products and heat from his muscles and deep tissues.

Bathe your horse. Bathe your horse in cool water, paying particular attention to his head, neck, “armpits,” and legs. As mentioned, large blood vessels in these areas flush heat to the skin surface. Avoid draping wet towels over his head and neck, which keeps heat in. Continuously apply and scrape water away until his skin feels cool to touch.

When cooling your hot horse, take a tip from endurance riders: Bathe him in cool water, paying particular attention to his head, neck, “armpits,” and legs, where large blood vessels flush heat to the surface.

Thumps. Thumps (synchronous diaphragmatic flutter) refers to a warning sign of underlying metabolic problems. It’s detectable as muscle twitches in your horse’s flank. If your horse suffers dehydration and electrolyte losses in the sweat, he may lose sufficient amounts of calcium, potassium, and magnesium ions in his bloodstream. When this happens, his phrenic nerve (which runs across his heart to supply nerve function to the diaphragm muscles) becomes more reactive, firing in synchrony with each heartbeat. This causes his diaphragm muscles to contract and “flutter.”  Sign of thumps: Sometimes, you’ll see no more than a flutter of the flank muscles as the diaphragm contracts. Or, you might feel a twitch in the flank area. Note that a horse may only thump on one side, and/or the thumping may occur intermittently. If you ignore this condition, and your horse continues to deteriorate with dehydration and electrolyte imbalances in the face of continued exercise, he could suffer myositis, colic, laminitis, heat exhaustion, and/or collapse. What you should do: If you spot any signs of thumps, dismount, and offer your horse feed and water. Keep your horse still. In many cases, rest, rehydration, and electrolyte restoration will resolve the problem. If symptoms persist, call your veterinarian.

Consider ice water. If you trail ride in a humid climate, you can cool your horse with ice water. Research from the 1996 Olympics in Atlanta, Georgia, shows that in hot, humid climates, you can apply ice water with little risk of muscle cramping, because humidity slows the cooling process. In more arid climates, however, ice water may cool your horse’s large muscle groups too quickly, resulting in myositis or “tying up.” (See “Heat-Related Conditions” on page 81.) To make sure he’s cooling down properly, check his rectal temperature; once his chest is cool to the touch, you can stop applying ice water.

Offer water. Offer a bucket of water to your horse following exercise. If you’ve been riding him at a fast gait, offer him small, frequent drinks until he’s cooled down a bit. But if you’ve been riding him at a slower, steady pace for a long period, encourage him to drink as much as he’d like.

Find shade. Lead your horse to a shady area, preferably where there’s good air circulation, such as a breeze. An enclosed space with stagnant air adds to heat retention.

Turn on a fan. Place a fan in your barn, and aim it on your horse in hot weather. As air flows across his body, it’ll help pull heat off his skin. As an added bonus, the fan’s breeze will help keep insects from pestering him.

Call your veterinarian. If your hot horse doesn’t cool down within 10 minutes, or his condition worsens, call your vet immediately. Heat stress can endanger your horse’s life. Your vet will likely give your horse intravenous fluids to treat dehydration and shock, and to cool organs and muscles.

Keep Your Cool

To help your horse stay cool and out of danger of heat stress, you’ll need to keep cool so that your thinking remains clear and you can take action in an emergency. Your ride will also be more enjoyable. Follow these tips to keep cool on the trail. Wear breathable clothing. Wear breathable clothing, such as cotton or manmade materials designed for hot-weather wear. (Non-breathable clothing will keep in your body heat.) Also look for clothing that blocks ultraviolet rays to help avoid sunburn. Drink plenty of water. Maintain your own hydration, drinking water frequently.

Consider electrolytes. Maintain your own electrolyte balance with sports drinks.  Eat for the heat. Maintain your energy level by eating power bars, fruit, and carbohydrates. Cool off. Buy a neckerchief with cooling gels. On the trail, wet the neckerchief with your drinking water or in a stream to activate the gels, and tie it around your neck. Also, soak your head before putting on your helmet and while on the trail. Take frequent breaks in the shade.