Heat Stress in Horses

Summer hot weather is here, and often with it hot and often humid weather which can cause horses to become overheated.

Horses produce large amounts of heat through digestion of their food and activity during exercise. If the air is cooler than the horse’s body temperature, then blood is directed to the skin where the horse rids itself of the excessive heat quite easily. However, the issue is when the air temperature is warmer than the horse’s body temperature, then sweating becomes the primary means by which the horse cools itself.  The horse is the only mammal, other than man, that cools itself primarily by sweating which wets the body so cooling, due to evaporation, can occur.

Serious problems develop and the horse’s cooling system breaks down during hot, humid weather when sweat does not evaporate and adequate cooling cannot take place. The result is heat stress or heat exhaustion.

What Heat Exhaustion Look Like

Symptoms of heat exhaustion include profuse sweating, muscle weakness, stumbling, rapid breathing and an increased body temperature of 102 degrees to 106 degrees Fahrenheit. The horse continues to sweat profusely, and despite the fact that his skin often feels cool to the touch, his body temperature is elevated and may remain elevated even after the horse has rested.

A much more serious condition is heat stroke, where the affected horse’s skin is hot and dry, breathing is extremely rapid and the horse’s body temperature may reach 106-110 degrees Fahrenheit. If untreated, horses experiencing heat stroke may collapse, go into convulsions and die.

If a horse becomes overheated, you should not attempt to differentiate between the two syndromes but should immediately stop riding the horse, place him in the shade and call the vet as the situation may quickly become an emergency. If there is no breeze, if possible provide air movement with a fan. Starting with the feet and legs, gradually wet the horse’s entire body, including the head, with cool water.  Small amounts of drinking water can be given at 15-minute intervals until the veterinarian arrives.

Preventing It

Heat stress can be prevented with proper management and conditioning. Calculating the heat index may alert the horse owner to unfavorable weather conditions where the horse should not be worked. To calculate the heat index, add 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. When the heat index exceeds 180, do not exercise horses because their body’s heat dissipation systems will not be adequate to prevent heat stress.

Horses not drinking enough water and not getting sufficient salt or electrolyte supplements are especially prone to overheating. Also remember that horses transported from cooler climates that have not had time to adjust to hot weather are especially vulnerable and should be provided adequate time to adjust to the warmer weather conditions. For those that give their horses feed high in protein, this generates extra body heat during the digestion process and make horses more susceptible to overheating.

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