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Horse owners encouraged to keep an eye on heat stress

by Wyoming Livestock Roundup

As summer progresses, temperatures begin to rise. And, while nice weather makes outdoor riding far more enjoyable, it can also be dangerous for horse health.

In an April 10, 2018 American Quarter Horse Association (AQHA) article, horse owners are reminded heat stress in horses is not something to take lightly since overheating can lead to a host of problems.

“Horses produce large amounts of heat, mainly through digestion of feed and muscular activity during exercise. If the air is cooler than the horse’s body temperature, blood is shunted to the skin where the horse easily rids himself of excessive heat,” explains AQHA.

“However, if air temperature is warmer than the horse’s body temperature, blood shunting is not enough, and sweating becomes the primary means by which the horse cools himself,” the article continues. “The horse is the only mammal, other than man, that cools itself primarily by sweating. This wets the body so cooling due to evaporation can occur.”

AQHA further notes problems develop during hot and humid weather when sweat doesn’t evaporate so cooling can’t take place. This results in heat stress, which leads to heat exhaustion or life-threatening heat stroke.

Heat stress in horses

According to AQHA, certain horses are more susceptible to heat stress. 

These include horses in poor condition, overweight horses, geriatric horses, horses in direct sunlight when the temperature is more than 100 degrees Fahrenheit or horses in hot, poorly-ventilated stalls or trailers.

Additionally, horses that don’t consume enough water or salt and horses transported from cooler climates to hot weather without time to adjust are at risk as well.

Symptoms of heat stress in horses include profuse sweating or less sweat than expected, hot skin, muscle weakness, stumbling, rapid breathing, rapid heart rates which don’t recover after exercise and increased body temperature of 102 to 106 degrees Fahrenheit.

Signs of dehydration may also indicate heat stress in horses. These include loss of skin elasticity, sunken eyes, tacky membranes and cessation of urination.

AQHA notes if a horse owner suspects their horse is overheating, they should stop riding immediately, move to the shade and call a veterinarian.

“If there is no breeze, provide air movement with a fan, if possible,” suggests AQHA. “Starting with the feet and legs, gradually wet the horse’s entire body, including the head with cool water. Avoid using cold water and never attempt a cold water enema. Small amounts of drinking water can be given at 15-minute intervals until the veterinarian arrives.”

The effect of feed and water

According to AQHA, one of the most important considerations to keep in mind regarding heat stress in horses is the effect of feed, water and critical electrolytes. 

AQHA explains rations high in protein generate extra body heat during digestion, which makes horses more susceptible to overheating.

“Horses produce large amounts of body heat during chewing, digesting and metabolizing feed, so avoid riding them too close to feeding time during hot weather,” AQHA says. “Heat generated during food digestion added to the heat generated by exercise could push them into heat stress. As a rule of thumb, feed horses three to four hours before exercising and wait at least two hours after they have been ridden before feeding.”

Additionally, the association notes lack of water will have the most profound and immediate effect on the well-being of a horse. 

“To put it in context, the body can lose nearly all of its fat and more than one-half of its protein content and survive, but a loss of just one-tenth of the body’s water can result in serious consequences,” AQHA states.

Preventing heat stress

With proper management and conditioning, heat stress in horses can be prevented.

The best way to do this, according to AQHA, is to calculate the heat index.

AQHA explains heat index can be calculated by adding the temperature in Fahrenheit and the percentage of relative humidity. 

“If the sum is below 120, there should be no problem exercising a horse. If the sum is between 130 and 150, the horse will probably sweat but should not experience any problems if he gets plenty of water to replenish fluid lost during sweating,” AQHA says. 

When the heat index exceeds 180, AQHA suggests not exercising a horse because the horses’ heat dissipation system will not be adequate enough to prevent heat stress.

AQHA further notes the single most important factor in preventing heat stress is providing plenty of fresh water and trace-mineralized salt. 

According to the association, horses drink around eight to 10 gallons of water a day. However, this amount doubles when temperatures rise, even without exercise. 

AQHA recommends providing extra water to penned and stalled horses and checking tanks at least three times per day.

“Research has shown horses working hard, such as endurance horses, can sweat nearly four gallons per hour under conditions of high heat and humidity,” explains AQHA. “Under normal conditions, a balanced ration and free access to mineralized salt are sufficient to replace electrolytes lost during sweating.”

However, equine sweat contains a large amount of sodium and potassium, and horses sweating excessively might not be able to replenish these electrolytes by merely consuming a salt supplement,” the association continues. “Therefore, provide a good electrolyte supplement to the feed of any horse working hard in hot weather.”

Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to

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