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Discipline: LD/Endurance, CMO, Trail Rider, Cartoonist, Writer, Co-Director/ Green Bean Endurance

January 22, 2010

The Cooling Mechanism

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My mental wanderings (between being gone to work for 13 hours yesterday) took me to an article written by Gayle Ecker, Heat Stress and the Endurance Horse the following are my take aways from this very well written article.

Sweat is what cools the horse, yes? Well- yes and no. Sweat is part of the mechanism of cooling, but it is actually EVAPORATION that cools the horse. This is why in hot and humid conditions we have so much difficulty cooling the horse because evaporation ceases. Interestingly, I did not realize that this applies also in temperatures as cool as 70 degrees F. If the humidity is high, regardless of temperature the horse will have difficulty cooling naturally (by evaporation).

Fluid out vs. Fluid in. Your horse will NOT be able to replace all of its fluid losses. Even the tanking up, slurping down, drinking well horse is going to have some fluid deficit. Based on equine physiology studies they concluded that 100% of horses will not be able to take in enough water to replace those fluid losses. So we are striving primarily to minimize fluid loss.

Water deficit is as much or more of an issue than electrolyte losses. When a horse becomes dehydrated the horse's blood volume decreases incrementally with the fluid loss. This reduces blood flow to the skin which in turn compromises naturally cooling through heat dissapation. Blood flow is reduced to the muscle resulting in decreased energy and less capacity for the removal of metabolic wastes (lactic acid), heat continues to build in the muscle as the fluid losses create loss of function on a cellular level. This sets up a situation that could result in tie-up. Next stop-the digestive tract. As fluids are drawn away from the digestive tract the horse becomes predisposed to colic.

So if water is the most critical component to our horse's well-being, and we are putting our horses into situations that will certainly create fluid deficit, what can we do?

*Electrolyte the horse prior to the competition to stimulate the drinking mechanism.

*Train in heat and humidity. Gradually expose the horse to the stressors that it will encounter on a ride.

*Slow down your pace on hot & humid days.

*Cool your horse at every opportunity between the vet checks. Sponging neck, chest, shoulders, and legs. Water applications should be scraped off, otherwise the water will act as an insulator rather than a cooling agent. Water on, water off.

*When gut sounds are bad (due to water losses) extend your hold time to allow blood flow to be restored to the gut, and the horse to begin tanking up on water, and eating normally.

*Be creative in getting water into your horse by adding grain rations, or other tasty things to the horses water. Feeding soupy yummy mashes, well soaked and soupy beet pulp, and soaked hay. Experiment at home and find out what your horse really goes for.

Gayle's article is well written, not overly technical, and a reminder that the most critical component to insuring a healthy horse at the finish is good old WATER.


  1. Good article. And the author is totally right - once you have heatstroke, your metabolism is never the same. I got heatstroke 16 years ago and I still overheat SO fast :(

  2. Me too...and I tend to cave in the heat, even when taking precautions. ~E.G.

  3. Clearly, the solution is to uproot your whole family and move west! ;) The dry heat is so much easier on me than the horrible steam-bath of a Memphis summer. And I think Indiana is almost as hot and humid, right?

  4. We are the Mecca of HOT & HUMID, you can pop a drenching sweat in July just by breathing. If you look at the ride calendar for July & August you will notice a gap...only an idiot would want to test the sweltering heat and humidity in Indiana during those two months. And if that isn't enough the deer flies and horse flies will eat you alive. West would be good :)