Newsdate: April 10, 2025 11:30 am
Location: GILROY, California

As the spring season moves on into summer,  warmer temperatures make it necessary for horse owners and care givers to pay special attention to how horses are affected by these increasing temperatures along with higher humidity.

Body of horse coated with sweat after a work-out in harness.

Profuse sweating, rapid breathing, and rapid heart rate are indications that a horse is heat stressed and needs to be moved to a shady area, allowed to cool down, and given water to combat dehydration.
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A combination of too much exercise and hot, humid weather are the common causes of heat stroke. When the sum of the ambient temperature in degrees Fahrenheit and the relative humidity is around 150, caution should be used in exercising the horse so heat build-up doesn't become critical.

Horses that are affected by anhydrosis (absence of sweating) are extremely susceptible to heat stroke, and special care should be taken with them since the most important mechanism for heat dissipation in horses is evaporation through sweat. In addition, horses that are unfit or overweight are more susceptible to heat stroke and exhaustion than more fit and lean horses.

When a horse's body becomes over heated either because of high temperatures or because of intense exercise under less than optimal conditions, it affects the horse's respiratory, vascular, nervous, and muscular systems and unless the horse is cooled down and lost fluids replaced, those systems will cease to function and the horse's body will shut down leading to severe damage or death.

Heat production can increase as much as 50% during intense exercise. The horse sweats to move more blood to the capillaries under the skin and breathing rate increases to release built-up heat. The horse's system may be unable to keep up with the mounting heat to the point that he becomes dehydrated.

Profuse sweating, rapid breathing, and rapid heart rate are indications that the horse is stressed and needs to be moved to a shady area, allowed to cool down, and given water to combat dehydration.

If the horse cannot be cooled down, the nervous and muscular systems will cease to function normally. When these systems stop functioning, heat stroke is inevitable unless measures are taken to cool the horse down and replace fluids lost because of sweating.

If heat stroke is suspected, the veterinarian should be called immediately and steps taken to cool both the horse and the environment.

Knowing the horse's normal resting and at-work heart rates, normal rectal temperature, and normal respiration rate can serve as a guide to prevent over-exercising a horse when the weather is hot and humid.

Normal vital signs for adult horses, according to the American Association of Equine Practitioners, are as follows: temperature: 99-100.8 F; heart rate: 28-44 beats per minute; respiration: 8-20 breaths per minute; rectal temperature: 101 F.

A simple pinch test can help determine if the horse is dehydrated. When a small section of skin on the horse's neck or shoulder is pinched and released, the skin should snap back into place. If there is a delay, the horse could be dehydrated.

Immediately move the horse to a cooler, shady area, and call the veterinarian. While waiting for the vet, cool water may be sprayed on the horse's legs and body, or towels soaked in cool water may be wrapped around the horse's legs and other areas that exhibit large veins.

In a critical situation, ice packs may be placed on legs. Fans to circulate the air may be used, and horses should be allowed to drink small amounts of water at frequent intervals. Walking the horse slowly will allow air movement to continue to help evaporate heat.