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Summer Stress: Helping Horses Handle the Heat

Depending on where you live, the same season can generate vastly different responses and management issues. Summer is a perfect example. Owners in northern states heave a sigh of relief that winter is finally gone and their horses can spend more time outside. Meanwhile, owners in states with notoriously long, hot summers are gearing up to help horses battle the heat and humidity.

Story originally posted by: Cynthia McFarland

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Evaporation is Key

“A lot of people use fans, but that really only works if the horse is already sweating.

You’re doing a better job of cooling him than with no fan at all, but if you have a hot, dry horse under a fan, you’re really just moving hot air over a hot horse,” Murphy explains. “You’d be better off using a mister and fan in the stall, or hosing the horse off and then putting him under the fan while he’s still wet. You need moisture in the air. Evaporation is the key to reduce body temperature. Using rubbing alcohol or body washes with the water will help because these evaporate faster than water alone; the horse gets cooler faster because the heat gets carried off.”

Fans blowing over a wet concrete aisleway will help drop the temperature in a barn, Murphy notes. Another temperature-lowering method is to put a soaker sprinkler on a metal barn roof. “If the water running off the roof is hot, then this is doing the job. To avoid wasting water, you can always collect it and use in it the garden or other areas.”

Heat = Stress

“It’s important to get horses out of the heat stress for at least a few hours every day,” noted Dr. Ralph Beadle, DVM, PhD, Professor Emeritus of Louisiana State University School of Veterinary Medicine. Beadle taught in LSU’s Veterinary Clinical Sciences Department of Equine Medicine for 25 years before retiring in August of 1999.

“Obviously if the environmental temperature will go down, that’s the best thing,” said Beadle. “If that won’t happen, there are other steps to take. A fan by itself in a shaded barn is good, but some barns get very hot. Misting fans provide a great benefit and will actually drop the barn temperature.

“If there’s a pond, horses will go stand in it and transmit the heat out of their body into the water. They’re smart about it.” Beadle adds that hot horses can be effectively cooled by hosing them with cold water. “There was the thought that you could throw them into shock, but there have been studies showing that using cold water works best (for cooling horses off). For the best effect, run cold water over the sides and bottom of the horse’s neck,” said Beadle. “This is where the arteries and veins are taking blood to the head and back to the heart again. When you cool the blood going to the heart, it sends cooler blood to the rest of the body.”

The danger in hot, humid climates is that horses who don’t get a break from the heat can become heat stressed (compromised sweating) and can even stop sweating completely (anhidrosis). “If you continuously stimulate the sweat gland receptors, eventually they quit responding,” said Beadle. “We see the problem here in Louisiana when the temperature doesn’t go below 70 at night, plus we have the high humidity to go with it. A non-sweater shuts down altogether, while heat-stressed horses still sweat some, but not as much as we’d like to see. If temperatures drop down into the low 60s at night for several consecutive days to weeks, then we’ll see them start sweating again.”

Dealing with Anhidrosis

When the weather is particularly hot and muggy, horses are often drenched with sweat even when they’re doing nothing more strenuous than grazing. They may not look it, but they are actually much cooler than the horse standing in the shade, panting, because he isn’t sweating.

Anhidrosis – the inability to sweat – has been recognized in horses since the mid-1920s. No definite reason has been discovered as to why some horses develop the problem, which can affect all ages and breeds. Anhidrosis is most commonly seen in horses living in Florida, Louisiana and south Texas.

Horses are designed to eliminate excess body heat and cool themselves by the evaporation of sweat. When a horse stops sweating, he tries to cool himself through a panting form of breathing. This forces cool air to move across his respiratory tract and when water evaporates from this surface, it helps somewhat, but is NOT an efficient method of cooling. Even at rest, the non-sweater’s body temperature may rise to between 102 and 103 degrees Fahrenheit. Add exercise to this dangerous equation and the animal’s temperature can reach 105 to 108 degrees. Brain damage is possible when the body temperature exceeds 106 degrees.

Signs of anhidrosis include panting, rapid breathing with noticeable flaring of the nostrils, decreased energy and sparse, dry hair coat, sometimes with scaliness or thinned hair on the face, neck and shoulders. Some horses will be sweating normally, even excessively for a few days, then shut down altogether, especially if they have just been moved to a hot, humid climate. A veterinarian can perform a “sweat test” to see how severely a horse is affected and to determine if the horse is actually a non-sweater or heat-stressed.

A combination of stressors can make a horse stop sweating. “We sweat tested a group of horses at a race track and examined one that was sweating fine on Friday,” recalled Beadle. “He raced over the weekend and chipped an ankle. By Monday this horse was not sweating; the combination of heat, stress and pain threw him into it. We don’t know if horses are genetically predisposed (to become non-sweaters), but we do know that environment plays a big part in it.”

The obvious, though often least practical, solution is to ship the non-sweater to a cooler, less-humid climate. When this is not possible, the key is careful, observant management, particularly before the animal stops sweating completely.

Providing fans in stalls and sprinklers in paddocks where horses can stand under a mist of water is advisable. Some benefits have been achieved through supplementing the horse’s salt by adding “lite” sale (potassium chloride) and commercial electrolyte formulas to the ration. Adding beer to the grain ration also helps in some cases.

Beadle notes that some people feel non-sweaters have an electrolyte deficiency. He suggests giving the horse two sources of water. This can be as simple as hanging two buckets – one with plain water, one of water with electrolytes added. “You want to give them both because some horses won’t drink water with electrolytes, and then they’ll get dehydrated by not drinking,” said Beadle.

Hanging two buckets in the stall will easily show you if the horse is drinking the electrolyte water. In certain cases when horses are severely deficient, your veterinarian may recommend administering electrolytes via nasogastric tube.

Research at the University of Florida has shown the value of One AC, a feed supplement consisting of L-Tyrosine, cobalt, niacin and Vitamin C, developed by Raymond LeRoy, a biochemist from Phoenix, Arizona. LeRoy theorizes that anhidrosis is caused by a depletion of dopamine in the brain. “The available dopamine is used first by the brain, second by the cardiovascular system and third, by the sweating system,” he said. “If the horse is not producing enough dopamine to satisfy all three, then sweating is compromised in favor of the brain and cardiovascular system.”

Best results have been obtained when horses were started on the supplement before they totally stopped sweating. LeRoy emphasized that horses must be taken out of training for approximately three weeks when initially started on the supplement. If reintroduced too soon, hard cardiovascular work will deplete the amount of dopamine necessary for stimulating the sweat glands.

Since there is no cure for anhidrosis, the best tools are observant horsemanship and sound management practices. Don’t work horses in the heat of the day. Avoid stressing horses in hot weather and back off hard work if the horse is showing signs of heat stress or diminished sweating. Provide practical options for horses to cool off.