Help your horse stay cool on the trailer and know what to do if he overheats

For many horse owners, warmer weather means more off-property trips to shows, clinics, trail rides, and other activities—some minutes away and others requiring several hours, or even days, of travel. As the temperatures rise, so does your horse’s risk of heat stress during trailering.

Heat stress can cause a horse to become unsteady on the trailer and, if left untreated, can lead to heat exhaustion or collapse. Learning to recognize the signs of heat stress in your horse before they become severe and understanding how to cool him if he experiences heat stress can help reduce the risk of severe complications.

Heat Stress in Horses

Heat stress is the horse’s response to dehydration—characterized by sustained skin “tenting” after a pinch test, pale and tacky mucous membranes, sunken eyes, dry feces, lack of appetite, and lethargy—along with extreme heat and electrolyte loss. Keep in mind, horses can become dehydrated due to loss of fluids through sweat in both dry and humid climates.

Horses with mild heat stress typically have a body temperature above 103 F and increased capillary refill time—the color of the gums takes more than two seconds to return after pressing them with your finger. Those suffering from severe heat stress can have a temperature of 106 F or more, elevated heart rate, thready pulse, and a lack of thirst despite being dehydrated.

If you believe your horse is experiencing heat stress, contact your veterinarian and formulate a plan to cool the animal as quickly as possible. Move him out of direct sunlight into an area with good airflow, continuously hose him, and offer a few sips of water multiple times (avoid him guzzling the entire bucket) to help him rehydrate.

Dangers of Hot Weather Trailering

“When horses suffer from heat stress they may become dehydrated, develop low blood pressure, can colic, or suffer from kidney compromise or failure,” says Ragan Adams, MA, DVM, veterinary extension specialist in the Department of Clinical Sciences at Colorado State University College of Veterinary Medicine and Biomedical Sciences, in Fort Collins. This is what might cause the horse to become unsteady on the trailer.

Check horses often enough that you recognize dehydration before they become unsteady and/or fall in the trailer, says Adams. Each horse that goes down in the trailer must be evaluated on an individual basis—some might get up easily with encouragement while others are unable to stand.

Another important issue to consider is horses with anhidrosis—the inability to sweat. Bob Coleman, PhD, associate professor at the University of Kentucky, in Lexington, recommends carefully monitoring affected animals during travel; watering them frequently; maximizing trailer ventilation (consider a more open-sided trailer); hauling during the coolest times and planning routes carefully to avoid traffic; and avoiding parking in the direct sun.

Before trailering any horse in the heat, discuss the risk with your veterinarian. Is the horse young and healthy or old with chronic disease? Adams says that before even loading your horse, ask your veterinarian to evaluate the ventilation in your trailer, and then plan on how you will respond if the horse shows signs of heat stress.

Mitigating Your Horse’s Risk

If possible, avoid trailering your horse on extremely hot and humid days. When the heat index (found by adding the air temperature and the humidity level) is at or below 130, healthy, well-hydrated horses can effectively cool themselves and should be able to safely travel, says Adams. However, when the heat index reaches 130-170, horses can only partially cool themselves. Older horses, those with chronic disease, and dehydrated horses are at a greater risk of developing heat stroke.

If the heat index is over 170, avoid trailering during the hottest parts of the day, or if the heat index reaches 170 during your trip, stop in the shade, unload if you’re in a safe place, such as in an enclosed area away from traffic, and cool and water your horse.

“Remember that in the trailer you have a horse that is giving off heat, so the temperature in the trailer will rise,” says Coleman, “compounded by the warm ambient temperature and radiant heating from the sun.” He compares this to a vehicle after it has been in the sun for a period of time—it is usually hotter than the outside temperature.

Whenever feasible, haul your horse during cooler times, says Coleman. “Starting early in the day or traveling at night may help (the horse) deal with higher temperatures,” he notes. Keep all windows and vents in the trailer open to ensure it is well-ventilated to remove built-up heat. “Plan your trip not only to avoid daytime heating but also traffic flow,” says Coleman. “You don’t want to be stuck in traffic in the heat of the day.”

Keep a wireless thermometer in the trailer that can be read in the truck and be aware of the outside temperature. Keep stops short and park in shady, well-ventilated areas. “Check the horse(s) at least every four hours,” says Adams. “Stop in the shade, offer water, unload if safe, walk the horses around, and spray them with cool water.”

Handling Heat Stress on Trailers

If your horse experiences heat stress on the trailer, again, find a safe, shaded, airy place to park and unload, says Adams. “Evaluate the horse thoroughly preferably out of the trailer,” she notes. “Look at the eyes for damage, dust, scratches, or dryness, evaluate capillary refill time, respiration rate, heart rate, gut sounds, manure status, body temperature, muscle shaking, and gait (for stumbling, lameness, or ataxia).”

As the horse cools down, offer him an electrolyte mixture (electrolytes in water can be absorbed faster) and reassess his vitals. However, if he is not used to drinking water with electrolytes, offer him plain water and administer an electrolyte paste, or provide electrolytes at the end of the trip. Once the horse is nearly fully cooled, offer him small bites of hay or grass, she adds.

Coleman says to be sure horses are not standing on pavement or gravel because these are hotter surfaces than grass. In this case, as well, offer your horse small drinks of cool water and, if possible, spray or sponge his body with cold water until he is cool.

Take-Home Message

If you must trailer your horse during potentially dangerous hot weather, consider your route, the time of day you will be traveling, and places to stop in an emergency, says Coleman. Travel in the early morning, late evening, or overnight hours if possible. “Check how well-ventilated the trailer is and make sure the airflow is as needed,” says Coleman. Be sure your tow vehicle and trailer are up-to-date on maintenance and safe for both you and your horse. Be mindful of how your horse is handling the temperature in the trailer during the trip, offer him water during stops, and monitor him closely for signs of heat stress.