Question: The long-range forecast shows a stretch of sunny days with temperatures in the mid-80s and high humidity. I’ve been schooling my horse in the early mornings or evenings, but he still works up a sweat. Dehydration is a concern. Is it enough for him to have plenty of fresh, palatable water and access to salt? What about giving him electrolytes to maintain hydration especially for the days when we’re schooling a little harder or having a lesson?

Answer: Electrolytes are common and essential salts that play a vital role in fluid regulation and nearly every other bodily function. They are lost in sweat primarily—at times showing up as a gritty, white residue on the coat when it’s dry—as well as in urine and manure. In many cases, a horse’s daily diet provides an adequate amount, but those who sweat profusely for a prolonged period will require a supplement to replenish what’s lost. Here’s how to determine what’s right for your horse and his particular situation.

All Systems Go

When dissolved in water or body fluids, electrolytes break up into ions (particles with electric charges). They carry signals across cell membranes and along nerve and muscle cells to support neurologic function, digestion and muscle contraction, including the heart. Electrolytes also move fluids into cells and waste matter out. They balance blood pH (acidity levels) and are integral to how nutrients are absorbed and how the body maintains its total fluid balance. Five electrolytes are essential for horse health: 

• sodium (chemical symbol: Na)
• chloride (Cl)
• potassium (K)
• magnesium (Mg)
• calcium (Ca).

Salt (NaCl), created when sodium and chloride combine, is required in the greatest amount, followed by potassium then magnesium and calcium. 

Intake, Loss and Replenishment

Electrolytes must be provided in the diet. Good-quality forage and a commercially formulated feed with balanced vitamins and minerals generally supply all a horse needs for a variety of circumstances, even when he’s working up a sweat. Such instances could include being turned out to pasture all day in the summer sun, covering a few challenging miles on the trail, doing some light work in the arena prior to a show or exercising intensely at speed for several minutes.

An electrolyte supplement will be warranted, though, when a horse’s level of exertion and the temperature and humidity cause him to sweat profusely for an extended time. That may seem to be a less-than-precise way to determine when he’s in need. But scientific research has been unable to offer specific recommendations because of the number of variables involved—ambient temperature, type of work, challenge of the terrain, how much an individual horse normally sweats. (One estimate puts the amount at four gallons an hour during hard work.)

The best gauge is to know your horse and the demands of his work. Then be mindful of the weather and monitor how much he sweats. If he’s in training and competing at a high level, the weather is scorching and he’s drenched, he’ll require an electrolyte supplement to restore what he’s lost. You can also rely on your veterinarian for guidance whenever you’re uncertain of how best to proceed.

There are other instances when an electrolyte supplement could be beneficial. They include:

• on the road to stimulate the thirst response of a horse who may be stressed and reluctant to drink while being trailered—especially for long distances over many hours—and experiencing unfamiliar surroundings
• preperformance to maintain the body’s fluid balance under the stress of competition
• post-performance to speed recovery from effort
• for diarrhea to increase water retention and decrease fluid loss
• when the weather changes—whether from cold to hot or vice versa—and a horse is disinclined to drink.

Forms and Formulations

Electrolytes for horses are available in several forms:

• pellets and powders to mix with feed 
• pastes and gels to administer orally with a syringe 
• preparations to dissolve in water.

The type of product you choose will depend on your circumstances and preferences—and what your horse will consume. For instance, pellets and powders may work well at home while a gel is handier when you’re away at a competition. Check a product’s label for a list of ingredients and details on administration. Ideally, an electrolyte supplement contains ingredients that mimic what’s found in horse sweat. Look for high salt content: sodium chloride as the main ingredient followed by potassium. Sugar is added to some products to improve palatability. It should be only a minor amount—no more than 10 percent of the mixture. (Tip: You can increase the palatability of a powder yourself by mixing it with molasses or applesauce before administering with a syringe.)

Whatever form you choose, keep in mind that electrolytes make a horse thirsty. He’ll need clean, fresh water available 24/7. That includes providing a bucket of plain water alongside one that contains electrolytes. (Check often to see that your horse is drinking the electrolyte water. He may not like an unfamiliar taste.) Also provide access to salt so he’s able to meet his own needs. He’ll be able to eat far more when it’s loose rather than in block form. 

Two Tests for Dehydration

1. Skin pinch: Pinch a fold of skin over your horse’s shoulder. It should snap back immediately. The longer it takes (2 to 4 seconds), the more likely he’s dehydrated.
2. Capillary refill: Apply pressure over an incisor on your horse’s upper gum. Remove your finger and notice how long the spot takes to recolor. Longer than two seconds is a sign of dehydration.

Other signs include fatigue, poor performance, decreased drinking and eating, reduced sweating, muscle weakness and tremors.

Practical Horseman thanks Jeannie Waldron, DVM, for her technical assistance in the preparation of this article. A graduate of the College of Veterinary Medicine at Tuskegee Institute in Alabama, she practices at Waldron Veterinary Services in Rectortown, Virginia. Dr. Waldron has national and international experience in the sport of endurance riding gained over a long career. She was inducted American Endurance Ride Conference Hall of Fame in 2004.

This article originally appeared in the Summer 2023 issue of Practical Horseman.