By Eleanor Kellon, VMD, staff veterinary specialist for Uckele Health & Nutrition

Many riders look forward to the summer season as the ideal time to ride or work their horse. Most understand the dangers of working horses under high heat and humidity conditions. However, horses can be compromised under less than sweltering conditions if you do not know how to protect them properly.

Dehydration through sweat loss is the major danger. Sweat loss totaling as little as a 3% of body weight can cause almost a 10% reduction in the horse’s exercise tolerance. For a 500 kg (1,100 pound) horse, that’s only 15 liters of sweat. Research has shown that a horse sweating heavily can lose as many as 16 liters of sweat in just one hour. Even horses working in milder weather conditions or horses turned out in hot weather and sweating can lose around four liters of sweat per hour.

Providing an adequate supply of palatable water is a huge factor in avoiding dehydration. However, water is only part of the answer. For the horse’s body to hold onto the required amount of water, electrolyte levels must be correct.

Sodium, potassium, and chloride are the major equine electrolytes. Bicarbonate is also important but the horse’s body can produce that from carbon dioxide and water as needed, and bicarbonate is not lost in sweat.

Calcium and magnesium are also lost in sweat but in much smaller amounts than sodium, potassium, and chloride. Sweat contains only a few hundred milligrams of these minerals, compared to thousands or tens of thousands milligrams of sodium, potassium and chloride.

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