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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Dear Doctor Warson,
Dr. Bob and Debby Miller headed me in your direction on Indian horsemanship which is part of my life. Now, I found your “heat” article. Would appreciate your advise on the technique I was raised with: We of Cherokee Nation soak a course woven hemp sack like a gunny sack with water and cover the horses back as he is hauled during hot weather. I do the same when hauling bulls to the sale as bulls nervous system seems to excite when handled. We do the same for our bodies except we jump in the creek or horse trough before working hay in the heat of the day. Sure seems to stay ciooler as the water evaporates. Thank you! Harold Wadley
Thanks for your comment. I have used this trick before, and it works well. The fibers in the sack provide a very large surface area for sweat evaporation. The sweat soaks up into the cloth and then evaporates. You are right,you need a coarsely woven fiber sack. Once the horse as cooled off, you can use the sack to rub the horse down, and see how their coat starts to glow!
Wadley sure wish you would have used this trick in RVN.
Doc
Recent articles have espoused the use of beer in cooling off anhidrotic (nonsweating) horses. This isn’t a bad idea, as it is palatable to the horse, and it dilates the blood vessels in the horse’s skin. This carries more body heat to the surface and allows it to be radiated off. Just be sure you aren’t in a blood or urine testing situation, as it will really light up the testing lab! JSW