EXERCISE AND DEHYDRATION IN THE HORSE

Abstract

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.