Every horse-person has seen and felt the white grit that remains on a horse’s coat long after he’s dried from sweating. But do you know what that is?
The grit is residual electrolytes that have left the body with the sweat and dried on the coat. It’s easy to see that the more the horse sweats, the greater the lost electrolytes. In fact, horse sweat is more concentrated in electrolytes than blood, which is the opposite of humans, so there is potential for extreme losses of electrolytes in exercising horses.
The major electrolytes in sweat are sodium, chloride, and potassium. Minor amounts of calcium and magnesium are also present, as are miniscule quantities of other trace minerals. Electrolytes are responsible for maintenance of acid-base balance and osmotic regulation of body fluids. Without electrolytes, the body is not capable of maintaining the right amount of fluid in and around cells. Although body fluid regulation is complex and involves enzymes, hormones, and proteins as well as electrolytes, the basic concept revolves around cell hydration. If cells lose too much water, they die. It is therefore important for the body to have an adequate supply of electrolytes, which means there could be times when supplemental electrolytes should be added to the diet of the horse.
A normal diet of forage will provide some electrolytes to the horse. By feeding a commercial feed (usually containing salt) and giving access to a salt block (or loose salt), all of a horse’s electrolyte requirements will be met under normal circumstances. In fact, the ingesta found in the large intestine acts as a reservoir of electrolytes for the horse to draw upon when needed. However, once the horse starts sweating a lot, whether it is with exercise or exposure to high heat, the reservoir may not be adequate in supplying sufficient electrolytes and, in this case, the horse will benefit from supplemental electrolytes. The quantity of electrolyte needed depends on how much the horse is sweating and for how long. Horses undergoing prolonged exercise like endurance or event horses may particularly benefit from electrolyte supplementation.
Electrolyte loss can result in dehydration. Testing for dehydration is simple: pinch a fold of skin over the shoulder and observe how slowly it returns into place. If the skin does not snap back quickly, measures should be taken to rehydrate the horse. Signs of more severe dehydration are unsteady gait, uncoordinated muscle contractions, trembling, and muscle weakness. The horse may lose interest in drinking even when dehydrated, because when both water and electrolytes are lost, the thirst response (the physiological trigger that tells a horse when to drink) malfunctions. Electrolytes are only part of the picture of fluid balance. Water is necessary and should not be overlooked when offering salt or electrolyte supplements; ideally, water should be available free choice so that the horse can drink when thirst hits.
When the horse is losing significant amounts of sweat, supplemental electrolytes can be given. A well-formulated electrolyte supplement should be mostly sodium chloride (salt). Other ingredients will be potassium chloride, calcium, magnesium, and other trace minerals. Typically, a little sugar is added to improve the palatability and was previously believed to improve the absorption of sodium, but that has since been found to be not completely true in the horse. If there is added sugar, it should not constitute more than 10% of the mixture, so as not to take away from the amount of electrolyte in the product. Most electrolytes can be mixed into a horse’s feed, mixed as a concentrated solution in a syringe, or added to water. When giving electrolytes in the feed or concentrated electrolytes in a syringe, it is extremely important to have free-choice access to water available so that the horse has something to drink when the electrolytes make it thirsty. Caution should be taken if adding electrolytes to the horse’s water; it is important to provide an additional bucket of plain water in case the horse refuses the electrolyte-laden water but needs to drink. Most horses have to learn to drink electrolytes in the water, and it is not usually something the horse will take to immediately.
Choose electrolyte supplements formulated by reputable companies. Kentucky Equine Research (KER) has developed several electrolyte supplements, including Restore SR and Restore Paste (Restore and Restore Paste in Australia), and Race Recovery (specifically for high-performance horses given furosemide; available in the U.S.). Other KER-formulated electrolytes designed for endurance horses are available in Australia.
Proper use of electrolyte supplementation can help maintain correct fluid balance in the horse when dietary electrolyte replenishment is too slow; so it is worth figuring out the best method of delivery of electrolytes for each horse before there is a critical moment of need.