I recently had the experience of shipping 2 horses in summertime from Hawaii to North Carolina. One could criticize this during hot weather, but half the trip was by ship, and calmer waters occur in summertime. The 2 week trip had enough layovers, but they still lost weight,  and have struggled to adapt to a hot,humid climate from a cooler, drier one. This prompted me to look into research on horse adaptation to heat and exercise, at least the practical parts of it.

Following the 1992 Barcelona Olympics, investigators from the University of Guelph decided to study heat resistance through training, acclimation, and nutrition. They found that 17 minutes of moderate exercise in a hot, humid climate were enough to raise a non acclimated horse’s temperature to 106 degrees Fahrenheit, a danger threshold. Further study and testing revealed that horses need 4 hours a day in heat, with activity preferably in the second hour, over a 3 week period to fully adjust. So much for those cool early morning workouts so favored in thoroughbred racing circles, especially since the races are run in the afternoon heat. A fully adjusted horse should be able to stand 4 hours’ heat exposure without  visible sweating unless exercised.

A horse’s water loss through sweating can be almost unbelievable. Just standing in hot weather can produce a 10 to 15 liter water loss each hour. Galloping and recovery can increase this to 30 liters an hour. Even trailering can result in 20 to 25 liters of water loss every hour. The latter is because the of the muscle contractions necessary to maintain balance in a moving trailer, and the heat they generate. The electrolytes lost in a horse’s sweat; sodium, potassium, and chloride are concentrated 4 time more than humans’. Good electrolyte solutions are commercially available. Given their cost, this author has had better luck with chilled Gatorade. Yes, chilled, since it has been shown that  chilled liquids can be drunk by an overheated horse without fear of colic. Cool water baths can also lower the temperature, but the water must be scraped off and then reapplied. This is because water will remove Latherin, the soapy surfactant in horses’ sweat which helps evaporation and cooling. The horse’s body heat will warm water sprayed on very quickly, so it should be removed mechanically.

We live for the joys of summer and riding our horses. We must be careful  not to  overheat them, and react appropriately if there is a problem.  A bucket, cool water, some electrolyte solutions, and a thermometer are the weapons you need to defeat the heat.

Keep riding    JSW

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