Photo 1: A rider cools her horse during a hot, humid ride in the Southeast. Horses doing moderate to more strenuous exercise
in these conditions can lose 30 pounds or more of body weight.
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At an equine endurance competition at Big South Fork National Forest in Tennessee this summer, the combined heat and humidity
pushed the heat index to a dangerous 150 degrees. Intense heat and humidity have been the norm for much of the country this
year, but equine athletic events continue to be held. During these dog days of summer, equine veterinarians must be aware
of and prepared to treat the potential problems facing equine athletes performing under these harsh conditions (Photo 1).
Often clients will consult their veterinarians regarding conditioning, nutrition, supplementation and managing horses exercising
in extreme heat. These recommendations have traditionally included electrolyte supplementation. Joe Pagan, PhD, of Kentucky
Equine Research calls electrolytes "essential nutrients for the performance horse," and adds that along with being essential
for maximal performance, electrolyte supplementation "helps horses rebound from hard work sooner, return to feed quicker and
begin the necessary rebuilding phase that occurs after exertion."
The essential elements of the electrolyte debate used to be which electrolyte mix to recommend, how much to use and when to
administer it. Recent developments from the world of endurance racing, however, have added another perhaps more important
question to this electrolyte discussion and might well affect how equine veterinarians advise their clients in the future.
Are electrolytes even necessary during a race?
The exceptional success of the French and Belgium endurance teams in recent international events has brought electrolyte use
into question, since both of these teams administer minimal to no electrolytes during a competition. "Electrolyting is only
the tip of the iceberg," says Leonard Liesens of the Belgium team. Riders from these countries are stressing harder pre-ride
conditioning and more complete feeding before competition as means of avoiding electrolyte supplementation during races.
Research shows that during the average 160-km (100-mile) ride in moderately hot weather, a horse will lose about 30 to 40
liters of fluid, which includes 300 to 400 g of sodium chloride, 45 to 50 g of potassium and a small amount of magnesium.
European veterinarians question whether this volume of loss can or should be replaced with the use of oral supplementation.
They reason that highly concentrated electrolyte salt pastes given by mouth contribute to both oral and gastric ulceration
and that this irritation can slow down the digestive process, which is a greater detriment to an exercising horse than any
potential electrolyte imbalance.
"Additionally, one of the more serious repercussions with overuse of electrolytes is that athletes will third-space fluids,"
says Heidi Smith, DVM, an equine practitioner working at an international level at endurance events. "In other words, they
begin to pull fluid back into the gut to bring the concentration of electrolytes there back to normal when they cannot transport
the electrolytes across the gut wall fast enough or when the concentration is already high in the bloodstream and cells because
of dehydration."
The end result may be that supplementation with concentrated electrolyte paste actually worsens dehydration in exercising
horses and contributes to metabolic problems rather than helping to avoid them.
The other side of the debate
Photo 2: Mobile scales such as these allow competitors to weigh their horses before, during and after competition to track
the volume of sweat lost and the relative success of their replacement program.
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The European approach is in conflict with opinions in the United States. Here, many veterinarians reason that electrolyte
supplementation will leave a horse less depleted at the end of a ride or event. They, therefore, recommend up to 10 doses
of electrolytes per race, which provides 120 to 280 g of electrolytes. This volume is suggested to be the equivalent of the
amount of electrolytes lost in 33 liters of sweat (Photo 2).
Photo 3: Horses at the 30-mile veterinary check of a 50-mile endurance ride replenish electrolytes and water with a diet of
primarily hay and beet pulp. It is crucial that horses replace both water and electrolytes during exercise in hot conditions
since either one without the other can still result in serious metabolic conditions.
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A key element, though, is that both electrolytes and fluids must be replaced for this system to work (Photo 3). The horse's
digestive tract motility must remain active, and sufficient fluids must be present to allow for absorption of the administered
electrolyte load. If a horse becomes dehydrated or if its digestive tract motility decreases, it is in a much more serious
metabolic situation if it has been heavily supplemented with electrolytes. Yet without enough electrolytes, the horse's digestive
tract function will decrease.
Research from the Ontario Veterinary College at the University of Guelph has shown that endurance horses and event horses
with less pronounced fluid and electrolyte alterations during a competition were more successful than those with greater losses.
This conclusion makes intuitive sense, and European veterinarians and riders would surely agree with these findings. But the
debate still rages on as to the best method of reducing fluid and electrolyte losses. And the best answer may turn out to
be the simplest.
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