HEAT STRESS: TOO HOT TO TROT? (excerpt from article)
by Dr. Jenifer Nadeau, Equine Extension Specialist – University of
Connecticut
Summer
heat and humidity can be very hard on horses, particularly working
ones. This is an excerpt from an article written by Dr. Jenifer
Nadeau, Equine Extension Specialist from the University of
Connecticut. Many cities around the world that have commercial
horse-drawn carriage rides have regulations that often do not factor in
humidity. This article discusses combining the temperature with
humidity as a guideline for working horses. The full article is
scheduled to eventually appear on the web site of the University of
Connecticut.
“Normally,
the horse cools itself by sweating. Heat is lost and the body cools as
sweat evaporates from the skin's surface. Less moisture evaporates in
times of high humidity, however, and this causes the cooling mechanism
to become less efficient. Prolonged exposure to high temperatures
results in dilation of surface blood vessels. When dilation occurs
without an increase in blood volume, circulatory collapse may also
occur. The cooling mechanism of the horse is most effective when the
sum of the ambient (outside) temperature and relative humidity is less
than 130. Efficiency of cooling decreases between 130 and 150. When the
sum of the ambient temperature and relative humidity is greater than
150, the horse's ability to cool itself is greatly reduced. When the
sum is greater than 180, horse owners need to be cautious, since these
conditions could be fatal if the horse is stressed. Some horses are
anhydrotic, meaning they have little or no ability to produce sweat.
These horses are prime candidates for heat stress.”
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