Managing Heat Stress

Happy Independence Day!  I hope everyone had a safe and fun holiday.  Now that we have celebrated our nations independence, temperatures this week will remind us that we are getting into the hottest part of the summer.  Here in North Carolina, we typically see our hottest temperatures of the year in July and August.  As the mercury rises, it is will become necessary to make adjustments to how we manage our horses to help them deal with the heat.

Fortunately, horses are effective at cooling themselves through sweat, and can acclimate to high temperatures.  However, monitoring and adjusting working and riding schedules is still necessary on hot days.  As you likely are aware, high humidity is very common here in North Carolina.  As the humidity increases, the ability of the horse to cool itself through sweating is decreased since evaporation decreases during humid conditions.  One good way to determine the cooling ability of a horse is to use the following chart, which uses the sum of air temperature and relative humidity:

Air Temperature (°F) + Humidity (%)	Horse Cooling Efficiency
Less Than 130	Most Effective
130-150	Decreased
Greater than 150	Greatly Reduced
Greater than 180	Condition could be fatal if horse is stressed

It is recommended to avoid riding and working horses when the cooling efficiency index is above 150.  This is common in North Carolina during the summer, for example, a 90-degree day with 60 percent humidity would meet these criteria.  If a horse must be ridden on hot days, here a few tips to help avoid heat stress:

·      Adjust you schedule.  Ride early in the morning or late in the evening.

·      Keep work light and allow frequent breaks.

·      Watch for normal sweating

·      Use fans to create airflow and work horses in the shade when possible

·      Provide access to cool clean water at all times, and offer frequent water breaks to your horse.

If overheating occurs there can be serious consequences.  An overheated horse will have a rectal temperature above 103 degrees.  If your horse is over heated, use a sponge or spray of water to help cool the horse, being sure to immediately scrape off excess water, and repeating until the horse has cooled.  Excess water should be scrapped away since water may serve as insulation, actually increasing body temperature.  If rectal temperatures reach 105 degrees, ice can be added to the water to increase cooling.  A rectal temperature above 106 degrees is indicates that heat stroke is likely.  Other signs of heat stroke include notable distress, muscle weakness, incoordination, extreme signs of dehydration such as dry mucous or a skin tent lasting 4-10 seconds, and collapse.  Heat stoke is a serious condition that will require emergency veterinary attention, including intravenous fluids with electrolytes.

To reduce heat stress in the summer, consider some of the following tips:

·      Provide turnout during cooler times of the day, such as night, early morning, and late evening.

·      Provide access to shade.  Remember shade from some structures may block airflow and reduce evaporative cooling.

·      Fans will help improve airflow, be sure plugs and cords are out of horse’s reach.  Misting fans can enhance cooling ability.

·      Ensure access to clean and cool water at all times.  Water sources may need to be cleaned more often during hot weather as bacteria and algae growth is more common during hot weather.

·      Consider adding electrolytes when heavy sweating is observed.  Offer access to clean water as well as some horses may refuse or drink less water containing electrolytes due to the taste. 

·      Clip horses with long coats to enhance cooling.

·      Transport horses during the coolest part of the day.  Never park loaded trailers in in direct sun, and ensure trailer are well ventilated and horses have access to water.

If you have questions about heat stress or cooling an overheated animal, please contact your extension agent.  If your animal is exhibiting signs of heat stroke, contact your veterinarian immediately. 

Article was adapted from “Managing Horses During Hot Weather” written by Krishona Martinson, PhD; Marcia Hathaway, PhD; and Christie Ward, DVM, PhD; University of Minnesota as well as Roy Johnson, MS; Cargill Animal Nutrition.  Original full article is available at http://www.extension.umn.edu/agriculture/horse/care/managing-horses-during-hot-weather/