This was on a list of things my horse's former owners were giving him on a regular basis, but in my experience, electrolytes were given to a horse in hot weather and/or after a heavy workout that resulted in a good sweat. They are, by nature, designed to replace those things lost in such situations.
Basically I want to know why I'm giving my horse a supplement, not just because someone else was doing it a certain way. If there's no benefit to him now, then I can better spend my money on a good all-around vitamin supplement.
If it makes any difference, this horse is coming off a neglect situation. He was pretty skinny this spring/summer, and while still underweight when I bought him a month ago, he is now thriving and nearly at 100% of his normal weight.