The intensity and duration of exercise has a major impact on fluid levels, electrolytes and acid-base balance in the horse. The changes range from rapid fluid and electrolyte shifts which accompany high-intensity exercise (VO2 max ≥ 100%) (i.e., racehorse) to substantial fluid and electrolyte depletion during Speed and Endurance Tests as seen at Three-day events. Depletion is also seen during prolonged endurance exercise, in which the horse performs a low-intensity form of exercise (30-60% VO2max). These fluctuations of fluid and electrolyte homeostasis have been implicated in the development of fatigue and can lead to medical problems when exercise is continued to a state of exhaustion. In racehorses, a rapidly increasing body temperature, an accumulation of acid, and associated electrolyte changes, specifically hyperkalemia, may be more important in contributing to fatigue than body fluid shifts. During prolonged, low-intensity exercise, fluid loss through sweating is a likely factor in limiting performance as it contributes to fatigue and heat-related medical problems, such adverse effects being greater when the horse exercises under hot and humid conditions. Treatments that aim to improve speed performance in race horses include dietary cation-anion balance (DCAB), furosemide and sodium bicarbonate loading. Offering an initial drink of salt water (0.9% NaCl) at 20oC after a few minutes of exercise (or at rest stops during the exercise bout or competition) is a strategy for rehydrating the horse which may be useful in hot and humid weather.
Faculty of Veterinary Science, Chulalongkorn University
"EXERCISE AND DEHYDRATION IN THE HORSE,"
The Thai Journal of Veterinary Medicine: Vol. 33:
4, Article 5.
Available at: https://digital.car.chula.ac.th/tjvm/vol33/iss4/5