It’s summertime – the time of year we look forward to! However, this summer we have been hit with so many extremes, from record-breaking heat to smoke from out-of-control wildfires in Canada to flash flooding, that it’s easy to come down with the summertime blues.

On days when we feel the heat, it’s important to think of your horse in order to prevent heat stress or even heat stroke, an equine emergency that occurs when outside temperatures and humidity are high. Other factors that can contribute to heat stress include prolonged exposure to sunlight without a source of shade, poor ventilation in the barn, excessive work (such as riding during very hot and humid weather), transportation in a trailer or van without adequate water and ventilation, long haircoats (such as in some older horses and those with Cushing’s disease) and being overweight.

It’s important to cool down your horse after each ride, no matter the air temperatures, for your horse’s general well-being – the heart, lungs and muscles. A horse will normally rid itself of excess heat by exhaling warm air and sweating, which causes the horse’s skin to become wet and allows for evaporation, which cools it down. Usually about 10 or 15 minutes of walking at the end of a ride will enable the horse to cool down slowly. After untacking, curry the horse and raise the haircoat to encourage heat loss, then offer fresh cold water. To cool an overheated horse you can also sponge it with water until its body feels cool or spray cool water with a hose.

Generally, an average adult horse at rest that weighs from 1,000 to 1,100 lbs. will drink six to 10 gallons of water each day. However, during the heat of summer, a horse will need to drink much more. Even at rest an adult horse should consume about 15 gallons of water, but a horse being worked or exercised in the heat may require twice that amount.

According to Iowa State University Extension’s Department of Equine Science, horses may lose one to two gallons of sweat per hour when trotting and cantering under mild temperatures. As temperatures and humidity increases, a horse can lose 2.5 gallons of sweat per hour. In addition to losing water, sweat includes proteins and minerals, such as sodium, chloride and potassium, known collectively as electrolytes. Electrolytes are responsible for maintaining the balance of fluids and circulatory function, facilitating muscle contractions, triggering nerve functions and helping to maintain the acid/base balance in a horse’s body. A deficiency in electrolytes can result in the horse eating less food and even drinking less water. Horses that do not consume enough water may become dehydrated and can suffer from overheating, tying up, fatigue, muscle weakness and even impaction colic.

There is a cure for the summertime blues

During the heat of summer it’s especially important to cool down your horse after exercise. Ten to 15 minutes of walking after a ride enables the horse to cool down slowly. You can also use a sponge or spray the horse with cool water to help prevent heat stress. Photo by Judy Van Put

Watch for signs of dehydration if you suspect your horse hasn’t been drinking enough water, or has been exercising in hot, humid weather. Check your horse’s skin to watch for elasticity by pinching the skin at the point of the shoulder and then release – the skin should return to its flattened state immediately. If the skin remains tented or compressed for more than two seconds, the horse is dehydrated. Other signs include dry, sunken-looking eyes; tacky or reddish mucous membranes inside the nose and mouth (these should be pink); lethargy; and lack of urination. If you notice any signs of dehydration, provide fresh, cold water and try to encourage them to drink every 10 minutes. Be sure that water buckets and outdoor watering troughs and tanks are cleaned regularly to remove algae and debris.

Anhidrosis is a condition where the horse is not producing enough sweat, which can cause their body temperature to rise above normal – to above 105º F or higher. Signs of anhidrosis include lack of sweat/a dry coat after exercise in warm weather, increased respiratory rate, decreased ability to work and an increase in rectal temperature. To prevent anhidrosis, don’t ride or exercise your horse in very hot and humid weather. Check with your veterinarian to see if medication or supplemental electrolytes are required.

According to Jennifer Rice, DVM, in her article “Heat Stress in Horses,” horses produce heat under two normal functions – digestion and exercise. However, the danger of heat stress occurs when the horse is not able to cool down normally or produce adequate sweat. Signs of heat stress include profuse sweating or sweating less than expected (anhidrosis); dehydration (as described above); stumbling and muscle weakness; skin that is hot to the touch; body temperature of more than 102º; rapid breathing; and rapid heart rate or pulse that does not slow with rest.

Heat stress can lead to life-threatening heat stroke if not treated. Symptoms of heat stroke include increased body temperature of more than 106º, continuing rapid respiratory rate, collapse and convulsion.

To prevent your horse from becoming overheated, make sure there is a good amount of shade to stand in, with proper footing below (clear of mud and muck.) Increase airflow through the use of fans in the barn, and if it’s necessary to transport horses, do so in the cooler times of the day, opening trailer or van windows and providing adequate ventilation. Be sure that horses have access to fresh cold water at all times. Ride in the mornings or evenings when the air is coolest. Keep an extra watch on older horses, who may not be able to regulate their body temperature adequately and clip horses that have long hair or shaggy coats.

Monitor the air temperature and humidity as a guideline for when to ride or exercise your horse during the heat of summer. The heat risk is minimal when the combination of the outside temperature (degrees Fahrenheit) and relative humidity is less than 130. When the combination is from 130 – 150, there is low risk as long as the horse replenishes fluid loss from sweating. However, you should avoid riding your horse when the combined air temperature and relative humidity is greater than 150, which is a moderate risk of heat stress. If the two factors together are greater than 180, do not exercise your horse at all, as this is a severe risk for heat stress.

If you suspect your horse is suffering from dehydration, anhidrosis, heat stress or heat stroke, contact your vet immediately. Checking your horse’s body temperature, heart rate and respiratory rate will provide helpful information for the veterinarian. Depending on the severity of the condition, horses generally recover from heat stress, after allowing a few days of rest and slowly getting back to their normal exercise schedule.

by Judy Van Put