How do I keep my horse safe in a heat wave?

That is the one line to remember from every source below. University of Minnesota Extension puts it flatly: heatstroke is an emergency, contact a veterinarian right away. UConn Extension adds that without cooling and emergency veterinary care, death can occur within hours.

Heat stress comes first, and it is the stage where you can still do the most. Minnesota Extension lists a rectal temperature above 103°F, faster heart and breathing rates, profuse sweating, droopy ears, tiredness, reduced appetite and dehydration. Its heatstroke signs include heart and breathing rates that do not settle within 20 minutes of stopping work, distress, dry gums, weakness, stumbling or collapse. UGA Extension and a New Bolton Center emergency vet writing in The Horse add one that surprises people: sweating a lot or not sweating at all can both be warning signs.

Heat stroke is not only an exercise problem. The New Bolton Center vet notes it can happen while a horse is simply standing in a hot stall or trailer.

The numbers below are Minnesota Extension's. Other extension pages give slightly different ranges, and Minnesota itself lists 106°F in one place and 'over 105' in another, so treat them as a guide to what is normal, not a line you wait to cross. The same page notes that rectal temperatures usually underestimate true core temperature.

Minnesota Extension names older, obese and out-of-shape horses, and says foals are more prone too. It also calls horses with anhidrosis, little or no ability to sweat, prime candidates for heat stress. UGA Extension lists high humidity, lack of water, long-distance travel and poor conditioning as contributing factors, and says mild heat stress may show no symptoms at all.

Long coats matter. Minnesota, UConn and UGA Extension all suggest clipping horses with long coats, including those with Cushing's disease, though the New Bolton Center vet cautions against clipping too close because some coat helps protect against damaging sun. If your horse does not seem to sweat properly, UGA says to consult your vet. That is a conversation to have before the heat arrives, not during it.

Horses moving from a cooler or drier place to a hot, humid one need time. Minnesota Extension allows 15 to 21 days for acclimation and says to keep monitoring the horse during that period.

UGA Extension calls keeping water available the number one way to prevent heat stress, and notes a horse working hard in heat can lose 2 to 4 gallons of sweat per hour. Minnesota Extension says an adult horse at rest in a cool climate drinks about 6 to 10 gallons a day, and more when working or in hot weather. It gives 45 to 64°F as the range for cool water. Clean buckets and tanks more often in hot weather.

A hot horse should not gulp. Minnesota's advice is a few swallows of cool, fresh water every few minutes, and it notes a horse's stomach holds only about 2 to 4 gallons without becoming overdistended. It also says not to withhold water from a hot horse.

Salt is where sources differ. The New Bolton Center vet suggests offering a salt block, or misting hay with salt water, if a horse is not drinking. Minnesota Extension suggests loose salt rather than a block to encourage drinking. On electrolytes, the sources agree on one safe step: if you add them to water, always offer a second bucket of plain water, because not every horse will drink the salty one. The New Bolton Center vet warns that too many electrolytes can be harmful, so ask your vet what and how much, and use only products made for horses (Minnesota).

A quick hydration check is the skin pinch. UConn Extension says to pinch the skin on the neck or shoulder: it should recoil within one to two seconds, and a longer delay suggests dehydration. Minnesota describes dehydration as a skin tent that lasts several seconds. A slow pinch is a reason to call your vet, not to experiment.

That sequence runs through the extension pages, with differences in the details.

UGA Extension's steps for an overheated horse: remove all tack and move him to shade; cold hose starting at the feet and legs and moving up toward the major veins (jugular, cephalic and femoral), which it says gives the maximum cooling effect; use a fan to increase evaporative cooling; offer fresh water at ambient temperature, not cold; and call a veterinarian if rectal temperature does not drop below 103°F. For a horse that has just worked, UGA also says to rinse from the feet upward and scrape off the excess water.

Minnesota Extension is more specific about temperature. For a rectal temperature above 103°F, spray the head, back, neck, rump and legs with a steady stream of cool water and repeat until he is cool. Above 105°F, it says ice can be added to the water, and that research shows this is safe, but not directly over the large muscles of the hindquarters. UConn Extension likewise says cold water is not harmful to an overheated horse. Minnesota says a veterinarian will often give IV fluids and electrolytes, and UConn says IV fluids may be needed, which is one more reason the call cannot wait.

Two cautions. Minnesota says not to put a sheet or blanket on a horse you are cooling. And the sources do not agree on every detail, such as cool versus ambient drinking water, so let your vet's instructions on the phone win. The New Bolton Center vet adds that frequent misting works better than a single hosing.

Minnesota Extension, UGA Extension and the New Bolton Center vet all suggest turnout in the early morning, late evening or overnight. The New Bolton Center vet adds that heat can reduce pasture quality, so you may need to add feed to maintain body condition.

Shade needs checking, not assuming. A run-in shed is best, says the New Bolton Center vet, and trees work only if they cover the horse at every hour, since shade moves with the sun. Minnesota notes buildings can block airflow.

Fans help. UConn Extension says restricting moving air in hot, humid weather is counterproductive, and Minnesota says misting fans are more effective. Every source that mentions fans adds the same safety note: keep cords and plugs out of the horse's reach.

Sheets and blankets are mostly out for the stabled horse. UConn Extension says to remove blankets or sheets from stabled horses during extreme heat. The exception the sources give is sun protection: the New Bolton Center vet suggests a fly scrim or fly sheet for horses prone to sunburn. Our scrim sheet explainer covers what a scrim is and is not, can I blanket a wet horse? covers coolers and covers after work, and our sunburn page covers the skin side.

Keep the routine otherwise steady. The New Bolton Center vet notes that too much change at once can invite colic.

Minnesota and UConn Extension say a sum under 130 is when a horse cools most effectively. From 130 to 150 cooling efficiency drops, above 150 it is greatly reduced, and above 180 it can be fatal if the horse is stressed. Minnesota says to avoid riding when the sum is over 150, especially for a horse that is not acclimated. UGA's example is 78°F and 80 percent humidity, which gives 158.

If you must ride, Minnesota's advice is early morning or late at night, light work with frequent breaks that does not exceed the horse's fitness, work in shade, and offer water often. It lists the signs that mean call a veterinarian right away: he stops sweating, breathes heavily, or becomes lethargic, distressed or uncoordinated.

Cool down on purpose. UGA suggests walking for the last 10 to 15 minutes of a ride, and the New Bolton Center vet says to remove tack as soon as you are done, offer frequent sips of cool water and sponge him with cool water. UConn says to walk a hot horse where air moves, not in an enclosed space where sweat cannot evaporate.

The rider needs a plan too. Our UPF riding shirt explainer covers sun-protective clothing for you, and a hot rider on a hot horse is a good reason to shorten the ride.

Minnesota, UConn and UGA Extension agree. Minnesota adds to offer water often. UGA adds that horses should not be left on a trailer for long periods. The New Bolton Center vet reminds owners that heat stroke can happen in a hot trailer.

If a horse arrives sweaty and breathing hard, treat him like any other overheated horse and call your vet if his temperature will not come down.