The 1996 Atlanta Olympics made many of us more conscious of the impact of heat on our horses. Heat stress is not just a factor in highly-tuned equine athletes; it may pose even more of a hazard if your horse isn't as well conditioned as he should be. Whether you're a daily rider or a weekend equestrian, the summer heat and humidity require extra precautions so your horse doesn't overheat during or after workouts.
Metabolism in horses is highly inefficient, with much more of muscle work, up to 80 percent, converted to heat and wasted. This sends a horse's body temperature way up, not only during his workout but for as long as 10 minutes after he's done. As his temperature rises, he begins to sweat, which allows the heat to transfer from the muscles to the surface of his body and dissipate as the sweat evaporates.
This process, which allows him to cool, becomes more difficult in high heat and humidity, especially when there's no breeze. When there is a great deal of moisture in the air, your horse's mechanism for heat loss, the evaporation of sweat, doesn't work as well. It is even more important to take some precautions during this type of weather to keep your horse cool during and after riding.
Although most of the research done in this area has focused on horses participating in three-day eventing because of the demands of the sport, the risk to more heavily-muscled animals such as those used in dressage and Western work can be just as great. It is significantly more difficult for those horses to cool themselves because of their dense builds.
Learn to Recognize Signs of Overheating
Horses follow a predictable pattern of symptoms when they overheat. When the horse is under saddle, the signs are harder to see, but a horse that is sweating, acting tired, stumbling, missing jumps, refusing work, having trouble breathing under saddle or trying to take extra breaths may be overheating.
The physical signs with the horse pulled up are easier to see. First, the animal responds to overheating by fast shallow breathing (hyperventilation) to dissipate heat through the lungs. This fast breathing will persist beyond the 10 to 15 minutes expected as a cool out time on a hot day. The horse becomes preoccupied, anxious, seeks water and will readily drink a gallon or two in most cases. At this stage, horses should be sweating from head to toe. If they are not, they may have a condition called "anhydrosis," which is a relative or absolute inability to sweat. These horses hyperventilate without sweating and require immediate cooling with ice water.
The body temperature of an overheated horse can exceed the normal 104 to 105 degree Fahrenheit that we expect after a hard workout, even going up to 107 F for longer than expected. High temperature like this can seriously impair tissue and even brain function. The first thing you want to do is stop work, take your horse to shade, loosen the girth and pull the bridle. Pour or sponge cold water or ice water onto the head, neck and chest. This will quickly reverse the signs. If there is wind, the horse will cool faster. If not, a fan helps, as shown in the Atlanta Olympics. Otherwise, use lots of water.
If the overheating gets worse, the horse may appear depressed, distant, even delirious. The respiratory pattern takes on a characteristic change, from fast and shallow to slow and deep labored breaths. This is an ominous sign and should be considered an emergency. At this point, the horse is failing to keep up with the heat overload and there can be harmful consequences.
If this stage is permitted to go on, the horse will become severely dehydrated, lethargic, weak and will show signs of electrolyte disturbances such as hypocalcemia (twitching, tremors, stiffness, falling down) or hypokalemia (arrhythmias, fast heart rate) or hypoglycemia (strange behavior, star-gazing or seizures). Seek immediate veterinary attention. Intravenous fluids, electrolytes, calcium and glucose may be administered.
Fortunately, most horse people will never witness these severe symptoms. It is far better to prevent the problem.