Horses rely on sweating to regulate body temperature. Equine sweat is more concentrated with salt (sodium and chloride) than other body fluids. As a result, horses can lose a lot of these electrolytes quickly when they sweat. Insufficient electrolytes contribute to dehydration, which can impair performance and inhibit proper cooling mechanisms. Therefore, maintaining electrolyte balance is essential.
What are electrolytes? Electrolytes help the body regulate water levels to maintain a balance between dilution and dehydration. The major electrolytes are sodium, chloride, potassium, calcium, and magnesium.
- Sodium and chloride. Important for maintaining blood volume. These electrolytes are lost in the greatest amount in sweat. Water follows sodium, so if sodium leaves the body in sweat, so does water. On the other hand, salt consumption encourages drinking.
- Potassium. Healthy horses require potassium for muscle contraction and relaxation. Horses with a specific genetic defect, called hyperkalemic periodic paralysis, may require a diet with limited potassium.
- Calcium. Essential for normal muscle function.
- Magnesium. Vital component of body fluids.
Because water follows sodium, sodium is key for maintaining hydration and fluid volume within the body. Here’s where it can get tricky: giving concentrated electrolytes to a dehydrated horse can actually worsen dehydration. Hypertonic solutions (solutions with a higher concentration of electrolytes than what is within the body) consumed orally will cause water to be drawn into the stomach and intestine until a balance of electrolyte concentration is achieved between the gut and the fluid outside the digestive tract. Therefore, the fluid remains in the stomach and intestine rather than in circulation. On the contrary, hypotonic solutions (those with a lower concentration of electrolytes than what is within the body fluid, such as water) can actually dilute body fluids, diluting the concentration of sodium and switching off the signal to drink.
A middle ground can be achieved, though. Isotonic solutions consist of electrolyte concentrations that are ideal for the body. Providing an isotonic solution is the most effective option for helping a horse replenish electrolytes and water in the body. Restore SR and Restore Paste, products available through KER, are designed to match the content of a horse’s sweat, helping to re-establish proper electrolyte balance and hydration. In Australia, look for Restore.
Horses lose approximately 10 grams of electrolytes per liter of sweat. Under ambient circumstances (not excessively hot, humid or cold), a horse weighing 1,100 lb (500 kg) may lose 5-7 liters of sweat (and 50-70 grams of electrolytes) per hour with steady trotting and cantering, but this can increase to 10-12 liters per hour of sweat loss in high heat and humidity. If enough electrolytes are lost, performance will begin to suffer. Exercise tolerance will decline, and conditions such as tying-up or thumps are more likely to occur. Electrolytes play a crucial role in muscle function, and both tying-up and thumps are conditions affecting muscles.
So, how do you properly supplement electrolytes? While there is a great deal of individual variation among horses, there are some general guidelines. For starters, all horses should have free-choice access to loose salt or a salt block. Good-quality forage should provide adequate potassium. Commercial grain concentrates generally do not provide enough sodium and chloride to meet the needs of a working horse, though there is typically enough potassium, calcium, and magnesium. Together, these feedstuffs should provide sufficient electrolytes for the average horse.
For horses training and sweating a lot, or if one is preparing for a long trailer ride or competition on a hot or humid day, an electrolyte with sodium and chloride as main ingredients should be introduced into the diet slowly. Electrolytes for heavily sweating horses can be administered 1-2 hours before work begins, and after 60-90 minutes of work. Keep in mind that ample, free-choice water should be available for horses to consume, as electrolytes stimulate thirst.
Contact a Kentucky Equine Research nutrition advisor for guidance on how to supplement electrolytes to best meet your horse’s needs.