Fluid and electrolyte balance in endurance horses.

In horses, fluid losses of 10L to 15L per hour can occur during endurance exercise under hot environmental conditions. The horse's sweat is hypertonic with respect to plasma, and large amounts of sodium, chloride and potassium are lost during prolonged exercise. Horses that reach exhaustive syndrome often show pronounced increases in plasma protein concentration. This could be an indication of failure of the compensatory fluid shift from the intracellular compartment caused by severe dehydration. Thorough physical examination by the ride veterinarian allows early recognition of dehydration and electrolyte imbalances.