Question: The weather is so warm recently, and I’m wondering if we should be concerned about heat stress in our horses. Do we have to wait until late in the evening to ride? We like to ride before dinner, usually around 5 or 6 pm for an hour or so, but I don’t want to hurt our horses! We’ve had both horses for about 3 months. One is a 17 year old Quarter Horse gelding, the other is a 15 year old grade (maybe Quarter Horse?) mare.

Answer:  High temperatures, high humidity, direct sunlight, and lack of breezes all contribute to increased risk for heat stress in horses (and people). Horses maintain their body temperature in hot weather by sweating. When the humidity is high, the sweat evaporates less quickly, and the horse cannot cool himself as efficiently. When high humidity combines with high temperatures, the horse is even less able to cool himself. Being out in direct sunlight intensifies the effect of both.

While I would normally recommend working horses during the coolest part of the day (usually early morning to before noon), it appears as though this might not suit your schedule. Most horses adapt to summer weather if given time to adjust gradually.  By using the tips to prevent heat stress below and a little common sense, there’s no reason you can’t enjoy your horse all summer long. If the weather is hot and/or humid enough that you can’t comfortably carry around a one gallon jug of water as you walk around the barn yard in the sun, you may wish to reconsider riding that day. Trails with lots of shade, arenas with good air flow and shade, and trails with shade and water to cross are some of the better choices in warm weather. Take water along for you and your horse if there won’t be potable water along the way, and watch for signs of heat stress so that you can prevent full blown heatstroke long before it happens.

Preventing Heat Stress

Having a fit horse is one of the most important aspects to preventing heat stress. An overweight horse that is being worked hard (or even a little) in hot, humid weather is far more likely to suffer from heat stress than a fit horse. Try to ride early in the morning, when the temperatures are generally cooler than evening time. Use as little tack as you need to for your riding purposes (lighter weight saddle blankets, limit the amount of leg wraps). Provide cool, fresh water. If you are riding in an arena, provide water at least every 15 minutes to half an hour, depending on how hard you are working your horse. If you are trail riding, take along a portable bucket and water if you won’t be coming across potable streams or creeks. You can try offering your horse water with electrolytes in it, but some horses will not drink it, so you should have plain, fresh water available too.

Detecting Heat Stress

Signs of heat stress include: difficulty breathing, elevated heartrate, appearance of distress (horse may appear lethargic or anxious, “droopy”, or may refuse to eat), weakness (general or muscle weakness), development of signs of colic or diarrhea, or stop sweating. 

The first thing you will probably notice in a horse that has begun to suffer from heat stress is an elevated respiratory rate. When the horse is “breathing hard”, air is forced past blood vessels in his lungs and airways, which helps cool the blood. While a minimal amount isn’t too much to be concerned about, his breathing should return to a more normal rate after a few minutes rest. If your horse’s respiratory rate is more than 40 to 50 breaths per minute and/or he’s breathing shallowly, with no improvement in his respiratory rate after a few minutes, take action to help him cool down.

An elevated heart rate helps move the horses’s blood toward the skin’s surface (to be cooled by outside air). If your horses’s heart rate is over 80 beats per minute (bpm) and doesn’t start to slow down after a few minutes rest, he may need assistance cooling off. An average resting heartrate is 30-40 bpm.

Horses will also sweat profusely in an attempt to cool off. When your horse is sweating over his entire body, he could be approaching heat stress. When he stops sweating entirely, he is dehydrated and most likely very heat stressed.

Horses may also have an elevated temperature after their normal methods of cooling have been overwhelmed. When your horse has a rectal temperature of 105 degrees Fahrenheit or higher, he could be in trouble. An adult horse’s normal body temperature is about 100 degrees F (99 to 101.5).

Your horse may appear physically tired and lethargic as blood is moved away from vital organs toward the skin to cool. Under heat stress, horses may become lethargic, stumble, or even collapse. The will usually have little or no interest in food.

The horse’s mucous membranes may become discolored. Blood pools in the horse’s gums as he tries to cool himself. If the horses gum are dark red or muddy colored, he is probably under a significant amount of duress.

Horses with severe heat stress should be moved into shade immediately. Stop your workout if you are working your horse, remove his tack, particularly saddles and saddle blankets. Call the vet if your horse is in serious distress. Hosing horses off with cold water will help decrease their body temperature, particularly if you aim for areas with large blood vessels close to the skin, such as the neck and inner legs. Don’t worry about him cramping up. You can also sponge bathe him if he resists hosing. A solution of rubbing alcohol:water mixed 1:1 will help him cool down as it’s sponged over him. He will cool off as the water and alcohol evaporate. Offer the horse fresh water to drink as you hose him down. Allow him to have as much water as he wants. Provide a breeze, use a fan if you need to. If your horses signs don’t improve or begin to worsen within 10 minutes of attempting to alleviate his symptoms, call your vet. Horses (and people) can be seriously affected by heat stress, and it can be life-threatening.

Horses can also suffer from sunburn (pink skin beneath areas of white hair are most often affected). Swollen areas, cracked or flaking skin, and scabs can all signify sunburn in horses. All pink skin on a horse is at risk, so if you have a paint or any other horse with a large amount of white, you may wish to apply a sunscreen or a fly repellant with sunscreen. One I’ve used in the past is Farnam’s Bite Free.

As another reference, check out this article, Trail Terrors, Part Four: How to Recognize Heatstroke, which was originally published in Horse & Rider magazine.