Electrolytes are electrically charged minerals that keep many of the body's automatic processes balanced and running.
Just as in humans, sweat triggers the natural and efficient internal cooling system in horses, a critical component for enduring hot conditions and periods of exercise. Of course, too much of a good thing has consequences.
Horses lose key electrolytes and proteins through sweat at a much higher rate than humans, and if not adequately replenished, can significantly hamper performance and potentially cause dehydration.
Ask the Vet: Is the Salt Block Enough?
By Monty McInturff, DVM - Tennessee Equine Hospital
Salt contains electrolytes which helps cool the horse and improves the cardiovascular system. It also helps oxygenate the horse. The salt block really does matter. White salt actually may not quite be enough.
When it's really really hot I encourage you to put an electrolyte supplement into the feed so that we know our horse is taking it in. Some horses are really great salt eaters and really great water drinkers, and some aren’t; so for [horses in heavy work] you should actually take an electrolyte pack and put a scoop into the feed. Be careful, some horses don’t take enough salt in. If you don’t take enough salt in, you tend to fatigue more quickly. Muscles need potassium, chloride, and sodium to help the cells recover while they’re working. It is very, very important.