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Fighting the Heat
By Dr. Dan Liebsch, Great Lakes Equine Wellness Center, Inc.
The hot summer months can be a dangerous time for horses. This is the time
of year when severe heat stress can occur in equine athletes. Although
horses can generally adapt to high temperatures, horses that are asked to exercise
during high temperatures are at a greater risk of experiencing heat stress. Horses
that are young, old, sick, or have a decreased ability to sweat are also at an
increased risk for developing heat stress.
Horses cool themselves primarily by sweating. The evaporation of the sweat
from the horse’s body cools the skin. Another mechanism for cooling involves
the dilation of small blood vessels in the horse’s skin to cool the blood. During
intense exercise, the heat produced by the horse’s muscles increases by as much
as 50%. If a horse is being exercised during very hot or humid conditions,
extra care must be taken to prevent heat stress. In addition, some horses
may have a life-threatening condition called anhydrosis, which means that they
are unable to sweat adequately.
 Signs that a horse may be experiencing heat stress include the
following: significantly elevated rectal temperature, labored
breathing, increased heart rate and respiratory rate, distressed
appearance, and sometimes signs of colic. For a horse
that is at rest, the normal range for rectal temperature is 99.9 – 101.5 F, heart
rate is 24 – 48 beats per minute, and respiratory rate is 10 – 18 breaths per
minute.
Heat stress can be life threatening if it becomes severe. Horses with very
severe heat stress can spike temperatures as high as 107 – 108 F. If you
suspect that your horse is suffering from heat stress, call your veterinarian. While
you are waiting for your veterinarian, stop exercising the horse and move him
to a cool shaded area that has a fan or breeze. Offer regular water and
water with electrolytes added. Repeatedly hose the horse’s legs and body
with cool water, being sure to scrape the water from the horse’s body afterwards.
If available, alcohol bathes (isopropyl) can also be helpful to lower elevated
body temperatures.
There are several things that can be done to avoid heat stress. Your horse
should always have access to clean fresh water to avoid dehydration. Try
to avoid exercising your horse during the hottest time of the day. Ride
early in the morning or late in the evening when it is cooler. When
riding your horse for a prolonged period of time, be sure to give him breaks
periodically with small amounts of water being offered. Monitor your horse
carefully, and stop exercising him if you believe he may be over-heating. Hose
your horse off with cool water after exercise to help cool him down. Providing
plenty of shade and ensuring good ventilation wherever your horse his housed
is also very important. If you believe that your horse does not sweat adequately
(anhydrosis), it is very important to call your veterinarian. Horses with
anhydrosis are at a much greater risk of experiencing heat stress. These
simple steps will help prevent your horse from experiencing problems associated
with heat stress.
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