A major concern with endurance horses is dehydration and electrolyte balance. During the ride, a veterinarian will examine all horses to determine if the horses are healthy enough to continue the event. Drs. Juli Flaminio and Bonnie Rush indicate in Veterinary Clinics of North America that clinical signs compatible with metabolic disturbances include dry, pale, or congested mucous membranes. Also, increased capillary refill time is common, and this can be checked by pressing on your horse's gums and removing your finger, then timing how long it takes for the pink color to return. Anything over 2 ½ seconds is abnormal. Loss of skin elasticity also occurs with dehydration; this can be checked by picking up the skin on the shoulder and releasing it, and the skin should immediately return to normal. If the skin remains tented for a period of time, dehydration is likely. A lack of urination and especially sweating indicates possible dehydration and many of these horses have decreased intestinal sounds, increased respiratory rate and an increased temperature usually related to a lack of sweating.
Also, many horses will have poor performance, depression, abnormal heart rhythm and faster heart rate than normal. The combination of dehydration, shock from low fluid volume, electrolyte imbalance and energy depletion leads to the exhausted horse syndrome. Without treatment, other symptoms that can occur include colic, laminitis, seizures, collapse and even death. Treatment of compromised horses involves intravenous or oral fluid therapy as well as electrolytes. Administration of water only without electrolytes can actually cause other problems and is not recommended.