South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Electrolytes for endurance horses - are they needed?
Schott HC*
Professor, Equine Internal Medicine
Department of Large Animal Clinical Sciences
D-202 Veterinary Medical Center
Michigan State University, East Lansing, MI 48824-1314
(517)-353-9710 [email protected]
Over the past two decades the variety of sports drinks and electrolyte supplements marketed to
support hydration in both human and equine athletes has expanded dramatically. However, it is
generally acknowledged that little, if any, fluid replacement is needed for exercise bouts lasting 2
h or less. For exercise lasting several hours human endurance athletes have been encouraged to
drink about 500 ml a couple of hours prior to exercise and small amounts (150-300 ml) of a sports
drink containing both electrolytes and carbohydrate every 15-20 min during exercise in an attempt
to limit dehydration from exceeding a 2% BW loss. This frequent fluid replacement is not driven
by thirst but by a conscious effort to drink in the absence of thirst. Of interest, this trend toward
“excessive” fluid replacement (drinking that is not driven by thirst) is not without controversy in
human sports medicine as it has become clear that excessive drinking of water or hypotonic sports
drinks is the cause of exercise-associated hyponatremia (EAH). EAH and EAH-associated
encephalopathy, now recognized as the leading cause of death in human endurance athletes, is
particularly a problem for slower athletes that exercise for a longer period and have a greater
opportunity (more time) for excess fluid replacement. Thus, perhaps it is fortunate that “you can
lead a horse to water, but you can‟t make it drink” because horses cannot be trained to drink in the
absence of thirst.
Exercise scientists opposed to the recommendation for excessive drinking by human endurance
athletes cite the fact that no data exist to demonstrate that dehydration >2% BW loss negatively
affects performance in endurance competitions or significantly increases the risk of development
of medical problems during or after competition. In fact, a study of 767 successful Ironman
triathletes found that athletes that lost the most BW actually finished faster.
Although electrolyte supplementation of horses competing in endurance events has become a
common practice, it warrants emphasis that, similar to their human counterparts, convincing data
to document that fluid and electrolyte depletion adversely affects performance is currently lacking
in endurance horses. Further, despite the favourable clinical responses observed with use of
intravenous fluids for treatment of horses that either are eliminated for metabolic disorders or
develop medical problems after competition, no data currently exist to document that affected
horses are any more dehydrated than successful horses. Despite a lack of supportive data,
supplementation of endurance horses with oral electrolyte slurries before, during, and after
competition is widely practiced and there is ev Y[