Page 106 - Speedhorse August 2018

AVOID HEAT STRESS AND STROKE IN HORSES
by Heather Smith Thomas
Heat stress, heat exhaustion and heat stroke are
terms that refer to dangerous conditions that may occur when horses are working hard in hot weather. Extremely hot and humid weather can pose a risk for horses, but is most likely to be life threatening when
a horse is exerting or being hauled in an enclosed trailer with inadequate ventilation.
Dr. Mike Foss of Alpine Veterinary Hospital in Oregon, says horses sweat primarily to cool themselves.
SIGNS OF HEAT STRESS
When a horse is too hot and unable to cool down, he may be lethargic and depressed. “After a workout, the horse may be breathing fast and not recovering as you’d expect. Delayed recovery might be the first thing you notice, along with him not wanting to eat,” says Foss.
Many of the signs of heat stress will be subtle and you may not notice them or realize their significance. “One thing you can do is take rectal temperature. Most veterinarians don’t consider a high temperature serious until it’s over about 105 degrees,” he says. If it’s that high, you’d want to check it again soon to see if it starts dropping. If the temperature doesn’t come down, the horse has not yet cooled off and may have a problem.
Severe heat stress/heat stroke is fairly uncommon in an arid climate, unless there is a heat wave that lasts several days. “When we do have that kind of heat, some people are caught off guard, thinking it won’t happen,” he says.
DEALING WITH HOT WEATHER
Shade for pastured horses and well-ventilated stalls that use fans with misters can be very help- ful. “These fans are readily available today. They are used at fairs and shows to keep livestock cool,” says Foss.
In severely hot weather, you might begin to see heat stress in horses that are not actively exerting. Horses that may be at risk include horses at pasture with no shade, horses being transported in a closed van or trailer in hot weather, and overweight horses. If you put up a roof for shade in a pasture, make it high enough to provide good air flow underneath or it may create an oven effect, especially if it’s a tin roof.
Kent Allen DVM, sport horse veterinarian in Middleburg, Virginia,
says misting fans may
be used in extreme
. . . when horses are working hard, we need to make sure they don’t run out of fluid and electrolytes and become dehydrated.
Dr. Mike Foss of Alpine Veterinary Hospital
in Hood River, Oregon, says horses sweat primar- ily to cool themselves. So, when horses are work- ing hard, we need to make sure they don’t run out of fluid and electrolytes and become dehydrated. Dehydration in hot weather can lead to heat stress.
Foss periodically talks to students at veterinary schools, discussing heat stress. He uses a diagram that shows the various ways heat can affect horses. “This includes radiation from the sun, reflection
of heat from the ground, generation of body heat from within, air temperature, and so on. There are many ways that horses can get too hot. In the arid west, we are fortunate because most of the time our horses can sweat to cool themselves,” says Foss. The dry air readily aids evaporation of sweat, tak- ing heat with it.
“About 80 to 90% of the excess body heat can
be dissipated via sweating, and a much smaller percentage can be dissipated via air exchange in the lungs. Horses breathe faster when they are hot to help facilitate that exchange. If they lose their ability to sweat, either through dehydration or increased humidity, they must utilize other ways to get rid of excess body heat and those ways are not as effi- cient,” he says.
“In hard-working horses, we worried when their respiration rate became higher than their heart rate. But today we realize the fast respiration in a horse
is simply the body’s attempt to cool off. We have learned that if we give the horse a chance to cool down, the horse will usually be fine. However, this does show that the horse is heat stressed, and we need to reduce the work load,” says Foss. “If a horse does not respond to cooling and rest, you may need to check for a more serious problem.”
Heather Smith Thomas
climate conditions to keep the horse cool enough. “Our first use of misting fans was in Atlanta, at
the 1996 Olympics, when we had to find the best way to cool the horses. If you are just spraying a hose in front of a fan, all you are doing is getting everything wet because
Sport horse veterinarian Kent Allen DVM, of Virginia Equine Imaging, says misting fans help keep horses cool.
104 SPEEDHORSE, August 2018
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