Symptoms give Warning of Heat Stress
Daytime temperatures for Oklahoma are soaring upward
into the 90s and approaching 100 degrees Fahrenheit; that means
horse owners will need to monitor their horses closely. Heat is
produced as a normal by-product in the daily metabolic processes
of horses, said Dave Freeman, Oklahoma State University Extension
During exercise, there is a significant increase in the amount of
heat produced by working muscles. Heat production estimates can
increase as much as 50 percent during periods of intense exercise
as compared with heat production when the horse is at rest. In
response, a horse increases its sweating rate, moves more blood
to the capillaries under the skin and increases its rate of
breathing in an effort to release this build-up of heat. "Heat
stress from exercise can result when the environmental
temperature is high," Freeman said.
Commonly observed signs of heat stress are profuse sweating,
rapid breathing rate and rapid heart rate.
Furthermore, some horses are anhydrotic, meaning they have little
or no ability to produce sweat. Since heat loss is mainly
dependent on convection (wind) and evaporation (sweating),
anhydrotic horses are prime candidates for heat stress. Freeman
said heat stroke can progress rapidly from heat stress if work
intensity, environmental temperature, humidity or anhydrosis
overloads the horse's ability to cool itself.
Symptoms include skin that is dry and hot, pulse and respiratory
rates much higher than normal and unusually high rectal
temperatures. "Heat stroke is life threatening," said Freeman.
"The owner should call an equine veterinarian immediately."
Freeman said the horse should be moved to a shady area with fans
or wind to provide ventilation. Cool water should be sprayed on
the legs of the animal's body to help the evaporation process.
"In critical situations, ice packs should be placed on legs and
other areas that exhibit large veins surfaces on the horse,"
Veterinarians normally will give large amounts of fluid to the
animal, and possibly give cold water enemas or drenches if the
core temperature is extremely high. "Normally, a horse's rectal
temperature is around 101 degrees Fahrenheit," Freeman said. "The
critical temperature, one that is characteristic of a
life-threatening situation if maintained for any length of time,
is around 104 degrees Fahrenheit."
The best recommendation is for equine owners to know how to
identify heat stress in a horse before it progresses to heat
stroke. Relieving the horse from exercise and cooling the
animal's body by fans and shade will help stop the onset of heat
stroke. "Also, care must be taken that the horse doesn't become
dehydrated during long bouts of exercise," Freeman said. "Large
amounts of fluid can be lost through sweat."
Freeman said the long-accepted practice of restricting drinking
water to exercising horses has little scientific backing.
"Generally, horses should be allowed to drink as frequently as
they desire, even during periods of exercise, unless they are
showing definite signs of heat stress," he said.
A hot horse may colic if given large amounts of water; since
horses should not drink large amounts when they are hot, riders
should offer small amounts of water to the horse in frequent
intervals before, during and after exercise. A simple test that
can be used to determine marginal water loss in a horse is the
pinch test. When a section of skin on the neck or shoulder is
pinched, the skin recoil will be immediate in normally hydrated
horses. Dehydration will delay skin recoil. Another practical
test is the "effective temperature" test, used to help determine
the environmental conditions most likely to result in heat
related illness in an exercising horse. This test combines
ambient temperature with relative humidity.
"When the sum of the ambient temperature in degrees Fahrenheit
and the relative humidity is around 150, the rider should use
caution in exercising the horse so heat build-up doesn't become
critical," Freeman said. Most riding activities involving long or
intense exercise should be postponed when figures approach 180.
Finally, it is important not to overlook cool-down periods
following exercise bouts, even when environmental temperatures
are well within normal parameters, Freeman said.
"Large amounts of heat build up in a horse during work," he said.
"This heat must be released from the horse's body through
respiration and sweat. "Heat loss through sweat requires
convection and evaporation. Freeman said the commonly used
practice of walking a hot horse guards against placing it in an
area void of air flow.
"Air flow is vitally important for convection of heat off the
horse's body," Freeman said.
The length of cool-down procedures will depend on the amount of
work, the environmental conditions and the individual horse.
Freeman said horse owners who use these simple procedures and
who know the signs of heat stress in horses can help prevent heat
stroke in their animals.
Article provided by Oklahoma State University