Keeping Horses Healthy in Hot Weather: Do You Know What Normal Looks Like?

There is something about a really hot day that changes the rhythm around horses. They find the shade. They move less. Water troughs suddenly seem much more important, and those of us caring for them start paying closer attention to the thermometer. We may change our riding time, turn on fans, fill buckets again, or hose a horse after exercise. Most of those things come almost automatically when summer temperatures climb.

But I think there is another part of hot-weather horse care that deserves just as much attention: Do you know what normal looks like for your horse?

Not simply what textbooks call normal. I mean this horse's normal. How quickly does your horse normally breathe while resting? How much does he usually drink? What do his gums normally feel like? How much does he sweat during exercise, and how quickly does his breathing settle afterward? Does he normally march back toward the barn looking for dinner, or does he prefer to stand quietly for a few minutes?

Those everyday observations become surprisingly valuable when temperatures rise, because heat stress rarely announces itself with one dramatic sign at the beginning. More often, the horse starts showing us that the work of maintaining normal physiology is getting harder.

What Is Your Horse Actually Trying to Accomplish?

A horse produces heat all day long simply through normal metabolism. Digestion generates heat. Muscles generate heat. Exercise can dramatically increase heat production, and then the horse needs some way to move that heat from inside the body into the surrounding environment.

This is where circulation, respiration, sweating, hydration, and the environment all start connecting.

Blood carries heat from deeper tissues toward the skin, where some of it can transfer into the surrounding air. Air movement helps that process. Sweating adds another powerful cooling mechanism because evaporation of sweat from the skin removes heat. Horses rely heavily on this evaporative cooling system, particularly during exercise, which explains why a horse can lose considerable amounts of fluid and electrolytes through sweat during hot-weather work.

That system works beautifully until the environment starts making the job more difficult.

Humidity provides a good example. We tend to focus on temperature because it gives us a convenient number, but 90°F on a dry, breezy day does not create the same physiologic challenge as 90°F with high humidity, direct sunshine, and very little air movement. When the surrounding air already contains a great deal of moisture, sweat evaporates less efficiently. A horse may sweat profusely and still struggle to release enough heat. A 2023 review of equine heat stress describes this relationship between environmental conditions, heat production, and the horse's ability to dissipate that heat.

That changes the question I want to ask when I look at a horse on a hot day. Rather than simply asking, “How hot is it?” I want to know how hard this particular horse needs to work to stay cool under these particular conditions.

Fitness matters. Workload matters. Humidity matters. Sunshine and shade matter. Air movement matters. Hydration matters. Even the individual horse matters. A fit horse doing light work early in the morning may handle a day very differently from an unfit horse working later in direct sun, even though both live under the same weather forecast.

This is one of those places where looking at physiology gives us a much more useful picture than looking at a single number.

The Early Clues May Look Pretty Ordinary

UC Davis lists several signs worth watching when horses encounter hot weather: a respiratory rate above 40 breaths per minute that doesn't come down after 10–30 minutes of rest, decreased energy or changes in mental activity, dry oral mucous membranes, prolonged capillary refill time, and quieter-than-normal gut sounds.

What strikes me about that list is how ordinary many of those observations seem. You don't need elaborate equipment to notice most of them. You need to know your horse and take a few minutes to look.

Gums provide quite a bit of information. Normally they feel moist and somewhat slippery. If they become dry or tacky, hydration deserves attention. Pressing gently on the gum causes the tissue beneath your finger to blanch, and normal pink color generally returns within about one to two seconds after you release the pressure. A delayed return gives us another clue that circulation and hydration may not look quite right.

Gut sounds offer another piece of the picture. Put a stethoscope—or simply your ear—against the horse's flank behind the ribs and listen. Normal intestines make noise. Those gurgles tell us that the gastrointestinal tract continues moving. A quieter abdomen, particularly when it occurs alongside reduced drinking, dry gums, decreased manure, lethargy, or other changes, deserves attention.

Respiration may tell us even more. Of course a horse breathes faster after exercise. The more useful observation comes from watching what happens during recovery. Does that respiratory rate steadily move back toward the horse's normal, or does the horse continue breathing rapidly despite rest and cooling?

That distinction between a physiologic response and the ability to recover from that response interests me in many areas of health. Exercise creates change. Heat creates change. Stress creates change. Healthy physiology adapts and then moves toward recovery. When recovery starts taking much longer than expected, the pattern gives us information.

This is why learning your horse's normal temperature, pulse, respiration, gum moisture, capillary refill time, drinking habits, manure patterns, sweating patterns, and normal recovery after exercise pays dividends long before anything goes wrong. UC Davis makes the same point in its guidance for horses traveling away from home: knowing an individual horse's normal vital signs makes changes easier to recognize.

Water Is Part of the Cooling System

There is an old piece of horse advice that still surfaces occasionally: don't let a hot horse drink too much water.

It sounds like one of those rules that probably began with good intentions and then traveled from barn to barn for generations. Current veterinary guidance tells us something different. Horses need access to water during hot weather, including before, during, and after exercise. UC Davis specifically identifies the idea that drinking water causes colic in a hot horse as a myth, and current Penn State equine guidance also encourages water during exercise, particularly when work becomes strenuous or prolonged.

The physiology behind that recommendation makes sense. Sweating requires water. Circulation requires adequate fluid volume. Blood helps carry heat from the body's core toward the skin. A horse trying to cool himself while becoming progressively dehydrated faces an increasingly difficult job.

How much water does a horse need? That depends on size, diet, activity, environmental conditions, pregnancy or lactation, and many other variables. UC Davis notes that a 1,000-pound horse at maintenance under moderate conditions needs at least about six gallons daily, while requirements can double or triple during high heat and humidity. Rather than treating any number as a daily prescription, I find it much more useful to combine general requirements with observation. Is this horse drinking more as temperatures rise? Is the trough dropping at roughly the rate you expect? What does manure look like? What do the gums feel like? Has anything changed from normal?

Heavy sweating adds another consideration because horse sweat contains electrolytes as well as water. Sodium and chloride losses become particularly important during prolonged or intense sweating. Electrolyte supplementation can make sense for horses losing substantial amounts through sweat, but electrolytes do not replace the need for water. UC Davis recommends continued access to plain fresh water when electrolytes are given and suggests working with a veterinarian when developing an electrolyte plan, particularly if you haven't used one before.

There is also an observation that can easily get overlooked: the horse who isn't sweating when you expect him to.

Inadequate sweating, or anhidrosis, interferes with one of the horse's primary mechanisms for dissipating heat. A horse who normally sweats and then begins showing unusually little sweat during conditions that cause other horses to sweat deserves attention, particularly if rapid breathing, exercise intolerance, elevated temperature, or prolonged recovery accompanies the change. Heat-stress research recognizes impaired sweating as an important concern because it limits the horse's ability to regulate body temperature.

Once again, knowing what normally happens with that particular horse gives the observation meaning.

Some Old Cooling Advice Deserves an Update

If you spent much time around horses, you probably learned some version of this routine: hose the hot horse, scrape the water off immediately, hose again, scrape again, and keep repeating the process. The explanation often involved the idea that water left on the coat warmed up and then acted like insulation, trapping heat against the horse.

This is one of my favorite examples of why we need to remain curious even about practices we've followed for years. Something can sound physiologically reasonable without actually working the way we think it does.

Research comparing cooling methods doesn't support the idea that water needs to come off before more water goes on. In fact, research reviewed in 2023 found cold-water application without scraping can cool effectively, and continuous water application offers an efficient way to transfer heat away from an overheated horse. The greater the temperature difference between the horse's hot skin and the cooler water, the more readily heat transfers into that water. Replacing the warmed water with more cool water continues that process.

Current Penn State guidance makes the practical recommendation wonderfully simple: during active cooling, keep applying water over the horse rather than interrupting the process to scrape after every application. UC Davis likewise recommends whole-body cooling and continuous application of cool or cold water, noting that research doesn't show a need to scrape excess water away during cooling.

That doesn't mean a sweat scraper suddenly becomes forbidden equipment. You can scrape a horse before putting him away if you want. The important distinction concerns the horse who needs active cooling. In that situation, stopping repeatedly to remove water doesn't improve the cooling process.

Air movement can help too. Water transfers heat away from the body while moving air supports convective and evaporative heat loss. Shade reduces the additional heat load from solar radiation. Research reviewed in the equine heat-stress literature found that horses without access to shade showed higher respiratory rates, rectal temperatures, sweating rates, and skin temperatures than horses with shade available.

Suddenly the familiar summer recommendations—water, shade, ventilation, lighter work, cooler riding times—look less like a collection of unrelated rules. Each one changes some part of the equation between the heat a horse gains or produces and the heat that horse can release.

Heat Stress Often Comes From the Stack

This may be the part of hot-weather horse care that matters most to me.

We tend to look for one culprit. Was it too hot? Did the horse work too hard? Was he dehydrated? Did the trailer get too warm?

Physiology rarely stays that tidy.

Imagine a horse who drinks a little less than usual overnight. Nothing dramatic happens. Then the next day brings higher humidity. The horse travels in a trailer for an hour, stands at an event in limited shade, and works harder than he does at home. Perhaps he isn't quite as fit as he was earlier in the season. Each variable by itself may remain manageable, but the horse doesn't experience them separately. His body deals with all of them at the same time.

This is what I mean when I talk about physiology stacking. Several relatively small demands can gradually reduce the body's room for adaptation.

Trailering deserves particular attention for this reason. A trailer creates its own environment, with restricted space, radiant heat from the roof and walls, body heat from the horses, and airflow that can change dramatically when the vehicle stops moving. UC Davis recommends traveling during cooler parts of the day when possible, maximizing safe ventilation, carrying water, and never leaving horses in a parked trailer during hot weather.

The same thinking applies at home. A run-in shed provides shade, but how much air moves through it? A barn may feel cooler because it blocks the sun, yet closed doors and windows can limit ventilation. Fans can improve airflow when installed and used safely, with electrical cords kept away from horses and barn wiring capable of handling the load.

Exercise becomes another variable we can change. Riding earlier in the morning or later in the evening, shortening a workout, building in more rest, or choosing not to exercise on a particularly hot and humid day can remove part of the physiologic load. Penn State specifically recommends considering not only weather conditions but also fitness level and workload when deciding whether exercise makes sense.

None of this requires fear of hot weather. It asks us to pay attention to context.

Perhaps Recovery Tells Us More Than We Realize

If you want one thing to observe more closely during hot weather, watch recovery.

Learn what recovery normally looks like for your horse after the kind of work you commonly do. Notice respiration, sweating, demeanor, interest in drinking, and how quickly the horse returns toward his usual behavior. If you safely know how to take temperature, pulse, and respiration, those measurements give you even more useful information.

Penn State identifies a rectal temperature above 103°F together with signs such as increased heart and respiratory rates, profuse sweating, exhaustion, or lethargy as indicators of heat stress that call for rapid cooling and veterinary attention. UC Davis likewise recommends prompt veterinary contact when dehydration, exhaustion, or heat stroke becomes a concern.

If a horse seems mentally dull, weak, unsteady, markedly dehydrated, unusually hot, or fails to recover despite rest and active cooling, don't wait for every possible sign to appear before calling your veterinarian. Continue cooling while seeking veterinary guidance when heat illness seems likely.

For the horse who appears well, though, hot weather gives us a wonderful opportunity to learn. Pick a few ordinary summer days and pay closer attention before you need the information. Count resting respirations. Learn how the gums normally feel. Listen to the abdomen. Notice water consumption and manure. Then watch what changes after exercise and how long those changes take to settle.

You aren't trying to diagnose disease. You're creating a reference point.

And that reference point changes the way we see our horses.

Instead of waiting for the obvious sign that tells us something has gone wrong, we begin noticing the smaller changes that tell us the horse is working harder to maintain balance. Perhaps breathing stays elevated longer today. Perhaps the horse seeks shade earlier. Maybe drinking changes, or recovery seems slower after a workload that normally causes little difficulty. One observation may mean very little by itself, but several changes occurring together start telling a more interesting story.

That, for me, is where prevention often begins.

We can't control the weather, and horses certainly don't need to spend summer wrapped in proverbial bubble wrap. We can control many of the conditions surrounding them. We can provide water and shade, improve airflow, choose sensible exercise times, cool effectively, plan our hauling, and recognize when the day's conditions call for a change of plans.

Most importantly, we can learn the horse standing in front of us.

Because the earlier question isn't always, “Does my horse have heat stress?”

Sometimes the much more useful question is:

“Is this still normal for my horse?”

The better we know the answer on an ordinary day, the more likely we are to notice when the answer begins to change.

OBSERVE • DISCOVER • THRIVE.™

References for Further Exploration

UC Davis Center for Equine Health. “Keeping Horses Healthy in Hot Weather.” 2020.
Practical veterinary guidance on recognizing overheating, hydration, electrolytes, exercise, trailering, shade, ventilation, and cooling horses with water. Veterinary guidance.

Kang H, Zsoldos RR, Sole-Guitart A, Narayan E. “Heat Stress in Horses: A Literature Review.” International Journal of Biometeorology. 2023;67:957–973.
A peer-reviewed review examining equine thermoregulation, detection of heat stress, environmental factors, and cooling strategies. Peer-reviewed research.

Penn State Extension. Danielle Smarsh. “Managing Horses in Hot Temperatures.” Updated 2025.
Current equine extension guidance covering hydration, exercise, environmental heat load, signs of heat stress, and rapid cooling. University veterinary/equine science guidance.

UC Davis Center for Equine Health. “Heat Advisory for Horses.” John Madigan DVM, Gary Magdesian DVM, W. David Wilson BVMS.
Veterinary guidance addressing recognition and prevention of dehydration, exhaustion, and heat stroke in horses.

OBSERVE • DISCOVER • THRIVE.™

Educational Disclaimer: This article provides general educational information and does not replace individualized veterinary advice, diagnosis, or treatment. If you notice changes in your horse’s health, behavior, hydration, temperature, or recovery—or suspect heat stress—contact your veterinarian promptly.

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