Horses exercising for extended durations at submaximal efforts often lose significant quantities of fluid and electrolytes in their hypertonic sweat. During endurance exercise, these equine athletes need regular supplementation of salts and ample water intake.
A study examined the effects of providing large volumes of fluid and electrolytes prior to exercise [Waller, A.P. and Lindinger, M.I. Pre-loading large volume oral electrolytes: Tracing Fluid and ion fluxes in horses during rest, exercise, and recovery. Journal of Physiology July 2021; https://doi.org/10.1113/ JP281648].
University of Guelph researchers administered a balanced hypotonic electrolyte supplementation containing radiotracer sodium and potassium ions in eight liters of water given through a nasogastric tube. They found that rapid absorption achieved plasma levels peaking at 45 minutes. After one hour, the ions were distributed to the extracellular space (ECF) and intracellular fluid (ICF). Nearly all sodium was sequestered in the extracellular blood compartment and the potassium was taken up into the intracellular skeletal muscle compartment by two hours of recovery.
Four healthy horses were included in the study, all previously conditioned to progressive exercise improvements over a four-month period. Each experiment was conducted in all the horses with two weeks separating each trial. The potassium evaluation took place about six months following the sodium trials.
Each experimental trial began with administration of electrolyte supplementation about four hours a er a morning feed, followed by exercise one hour later. A radiotracer was injected via an intravenous catheter one hour prior to start of exercise. Ingredients of the administered powdered electrolyte (Perform’N Win by Buckeye Nutrition) included sodium chloride, potassium chloride, magnesium sulfate, dextrose, sucrose, calcium citrate, fumaric acid and citric acid.
A sweat wrap was placed around the barrel of each horse 30 minutes prior to start of exercise to facilitate collection of sweat. Ten minutes before exercise, a muscle biopsy was obtained from the gluteus medius muscle. Horses performed exercise under controlled indoor conditions of 68-73.4 degrees Fahrenheit and 50-65% humidity. After walking for five minutes, the treadmill speed was increased to 5.5 mph, then to an intensity designed to maintain a working heart rate that approximates 30-34% of peak VO2 for sodium and 50% of peak VO2 for potassium. The average speed of 6.7–9 mph on a 1.5-degree incline pushed the horses to a point of voluntary fatigue in which they were unable to keep up with belt speed. A hi-speed fan continually blew air at the horse during roughly 105 minutes of exercise.
Blood and sweat were analyzed from pre-exercise rest, during exercise and during recovery. Body weight taken prior to and after exercise helped to calculate body water losses at rest, at end of exercise and after two hours of recovery. The horses were not allowed to drink until the end of sampling post-exercise.
The authors concluded:
- Pre-loading with two gallons of electrolyte supplementation in water an hour prior to the start of exercise facilitated an increase in exercise duration and sweating despite continuing sweat losses of fluids and electrolytes.
- Compared to plain water, an electrolyte supplement better maintained plasma volume and ECF volume during submaximal exercise.
Electrolyte supplementation also increased sweat losses of sodium, potassium and chloride.
Electrolyte supplementation in two gallons of water one hour prior to exercise allows uptake of water and ions by muscles and soft tissues to attenuate body fluid losses and to maintain sweating rates. This has the potential to improve cellular function and thermoregulation during exercise.