Electrolytes for Horses: How Much, When, and Why Salt Beats Sugar
Horse sweat is not like human sweat, which changes what replacing it requires. It also explains why a lot of what is sold as electrolytes is mostly something else.
Most advice about electrolytes for horses is borrowed from advice about electrolytes for people. It should not be, because the two species sweat quite differently, and the difference is the entire point.
Horse sweat is more concentrated than human sweat
Human sweat is dilute relative to blood. Sweat heavily as a person and you lose a great deal of water and comparatively little salt, which is why the standard advice for people is mostly about drinking.
Horse sweat is not dilute. It carries a higher concentration of electrolytes than the horse's own blood plasma does. A sweating horse is losing significant quantities of sodium, chloride and potassium, along with smaller amounts of calcium and magnesium, at a rate that a person doing similar work would not.
That single fact reorders the advice. For a horse in real work in real heat, replacing the water alone leaves the job half done.
The thirst problem
There is a second order effect worth understanding, because it catches people out.
Thirst is driven substantially by sodium concentration. When a horse loses a large amount of salt in sweat and then drinks plain water, the water dilutes what is left. The body can read that as a resolved situation and reduce the drive to drink, while the horse is still down on both fluid and salt.
This is why a hard working horse in hot weather can look like it is not especially thirsty while still being behind. Replacing salt is part of what keeps the drinking mechanism working properly.
Water without salt can switch off the thirst that would have replaced the water.
Why so many products are mostly sugar
Pick up an electrolyte supplement and read the ingredients in order. A great many of them lead with dextrose, glucose or another sugar.
There are reasons a small amount is included. Sugar aids absorption to a degree and it makes the product palatable, which matters with horses. But a product that is predominantly sugar with electrolytes added is being sold at a considerable premium over what is actually doing the work.
The ingredient list is in descending order of quantity. That one habit tells you most of what you need to know about any given tub.
What most horses actually need
For a horse in light work, in normal weather, with free access to clean water: plain salt, and not much thought beyond that. A salt lick, or salt added to feed, covers the ordinary case. Sodium chloride is the electrolyte lost in the largest quantity, and it is the cheapest thing in the entire category.
For a horse sweating heavily, in sustained heat, or working hard for long periods, a proper electrolyte supplement earns its place, because potassium and the others are being lost in quantities that plain salt does not address.
Two practical rules matter more than the product choice. Never give electrolytes to a dehydrated horse without water freely available, because concentrating salts in a horse that cannot dilute them is the wrong direction. And introduce anything new gradually, since palatability varies and a horse that refuses its feed has gained nothing.
The honest summary
Electrolyte supplementation is genuinely useful for horses doing genuinely hard work in genuinely hot conditions. For most horses, most of the time, the answer is salt and clean water, and the sophistication belongs in making sure they actually get both.