March / April, 2002
Horses and Hot Weather
Minimizing the stress associated with working under high temperatures can be a key to helping a horse function at its very best during the summer season. Understanding how heat moves from a horse to its environment and vice versa-conduction, convection, radiation and perhaps evaporation-will help you.
The bodily functions of a horse depend upon its capacity to maintain a long-term normal internal body temperature within a degree or two. One of the products of digestion is heat. Therefore, a critical function for a horse is being able to constantly expel heat to the environment. As long as the surrounding environmental temperatures are below its core body temperature a horse can lose heat by conduction by being in direct contact with cooler surrounding air, ground or floor. But, conduction alone does not play a major role in heat loss.
More important is convection-the horse loses heat when cooler air moves over its body. A difference in temperature is the driving force that influences how rapidly the heat loss occurs. With convection, it is the difference in temperature between the hair coat or skin that may be exposed to the air and the air temperature. As the air temperature approaches the skin or hair temperature, the rate of heat loss by convection slows down.
Fortunately the rate of heat loss by convection is also influenced by how rapidly the air moves past the animal. A horse on pasture can choose to be in a location where the wind is blowing-assuming a wind of course. The horse could choose to run, but that generates more heat and is not helpful in getting rid of heat!
A horse can lose heat to surfaces that are cooler than its hair coat surface by radiation also.
When horses are in a barn, rapidly moving air past the animal makes all the difference. During warm weather, alley doors and windows are opened to increase the volume of airflow. But is more air actually moving over the horse? We may stand in the alley where there is a breeze. But horse stalls that have a major portion constructed of solid material along the alley reduce the amount of air that comes from the alley to the stall. Solid dividers between stalls limit how much air gets from one stall to another and stops air from actually going over the horse. Many times windows in horse stalls are located high on the outside wall to keep horses from damaging them. However even though the windows may be open the air blows in and out of the barn without coming into direct contact with the horse and does help heat loss by convection.
Next time well talk about the ace in the hole for horse-perspiration and evaporation.
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