Helping Your Horse Survive the Heat: A Guide to Electrolytes

Photo by Alain Moreau on Unsplash

By Clair Thunes, Ph.D.

As I sit in my air conditioned office writing this article, it is 106 degrees outside. Summer has arrived in Northern California! Some areas of the country such as Florida and Arizona have been experiencing the effects of summer for some time, and the more northern states will be there soon enough. When the heat gets turned up questions about electrolytes are not far behind. Here are the answers to some common heat-related questions.


Sweating is a key cooling mechanism for your horse just as it is for you. About 70 to 80 percent of energy consumed by your horse is lost as heat. And, because exercise requires energy, it results in heat production. If unable to remove heat, the horse would be at risk of overheating within as little as 10 mins. Unlike dogs which are not good at lowering body temperature (this is why it is so important not to leave them in hot cars!), horses are able to reduce 55 -70% of exercise generated heat through evaporative sweating and another 25% through exhalation. Without the ability to sweat, your horse is unable to prevent overheating. This is why the non-sweating condition anhydrosis is a big concern. If other horses are sweating and your horse is not, you should discuss the situation with your veterinarian.


Interestingly it is not. Horse sweat contains much higher concentrations of electrolytes than human sweat which is part of what can get them into trouble. As they sweat, they lose large amounts of chloride, sodium, and potassium, and lesser amounts of calcium and magnesium. High circulating sodium concentration is one of the things that will trigger a horse to drink. However, if your horse has lost a lot of sodium in sweat, then circulating sodium concentration drops and the desire to drink disappears. As a result, even though a horse has lost a lot of fluid sweating, he may have no desire to replace that fluid. Hence, you can lead a horse to water but you can’t make him drink.


Electrolytes dissolve in solution and once dissolved are able to conduct electricity. Due to their conductivity, they play important roles in regulation of nerve and muscle function. Electrolyte levels directly impact muscle function. Electrolytes have many other functions within the body including maintenance of fluid levels within and around cells, controlling blood volume, absorption of nutrients across the digestive tract lining, digestive tract secretions, and organ function.


There are some simple tests you should be familiar with that can help you determine if your horse may be dehydrated. There is the skin pinch test where you pinch some skin on the horse’s neck, let it go and it should immediately spring back flat. If it remains “tented” this is a sign of dehydration. Note that this is not the most reliable do-it-yourself test because as horses age their skin gets thinner and may spring back quickly even when dehydrated. Another method is to check capillary refill time. For this you raise the horse’s lip exposing the gum tissue and gently press your finger into the gum. The gum will appear white on removal of your finger. Then, time how long it takes for the gum tissue to re-perfuse and return to its original salmon pink color: ideally 1 to 2 seconds. Other indicators of dehydration include eyes looking dry or dull and sunken in, flanks appearing drawn up, manure being hard, mucus membranes feeling dry or tacky to the touch, lack of urination and or dark urine, lack of desire to drink, overheating, increased heart rate and respiration. You should check with your veterinarian if any of these symptoms are present.


There are two parts to providing ample electrolytes. First is to insure that you are meeting your horse’s baseline maintenance needs. Second is to replace electrolytes lost in sweat. While your horse’s forage and other feeds may fulfill his needs, unless you have had your forage tested this is not guaranteed. You may provide a salt block and believe that this is covering your horse’s baseline needs. However, unless he is going through a 4 pound block every other month that is not the case. While salt should be available at all times, the addition of 1 tablespoon of salt per 500 pounds of body weight to your horse’s ration each day is a wise choice. This will cover maintenance requirements.

On days when your horse works hard or the weather is so hot that he is sweating while just standing around, you should add an electrolyte in addition to the salt. The purpose of the electrolyte is to replace sweat losses. In hot weather and for hard working horses this may mean that you are giving an electrolyte every day. For others it may be less frequent. Many people make the mistake of only giving electrolytes during competitions. However, if you have been training hard in the weeks before without replacing sweat losses, your horse will not be able to replace those losses in time for maximum performance.


This is really key. For a product to have any impact on replacing sweat losses it must contain adequate levels of the necessary electrolytes. As these are not particularly palatable, there is a tendency for companies to include sugar to improve palatability. If the list of ingredients puts sugar or dextrose as the first ingredient, keep looking! You want to find a product that mirrors the composition of sweat and provides more chloride than sodium or potassium. Calcium and magnesium may or may not be included.

Photo by Bob Letens on Unsplash


I like to put them in feed but you can also put them in water. If you put them in water always insure that you provide water without electrolytes as well. Paste products are available and these are a great way of ensuring that your horse gets the electrolytes necessary.


If you have given your horse electrolytes and he has not consumed any water, do not give additional electrolytes without consulting your veterinarian. If your horse is already dehydrated and you continue to give electrolytes, it may worsen dehydration as fluid will be pulled out of cells to dilute the electrolyte levels in the blood. With a good daily electrolyte management program, this problem is less likely to occur.


Glycogen in muscle tissue, the storage form of glucose, requires water so hydration is critical for energy store replenishment. Dehydrated horses will not be able to replenish lost energy store, negatively impacting performance. This is especially true in competition environments where horses may be working hard every day. Remember you may not be able to tell that your horse is mildly dehydrated, but it will be impacting body functions whether you can see it or not.

Trailering especially for long distances can cause a surprising amount of sweat loss. One expert reports that a 10 hour ride in a trailer can lead to 18 liters of sweat loss. This could put your horse at a disadvantage before you even start a competition.

Humidity really ups the ante because it reduces the body’s ability to dissipate heat through evaporation and so horses are at greater risk of overheating. It takes about 3 weeks for horses to adapt to significant climate changes so be very careful if competing in unfamiliar climates especially if you are facing humidity.

In conclusion, a good electrolyte protocol used in combination with careful management and common sense will allow your horse to keep competing in the heat to the best of his ability.

Clair Thunes, Ph.D. is an independent equine nutritionist and owner of consulting company Summit Equine Nutrition LLC based in Sacramento, CA. She works with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses. She can be reached via her website

This article originally appeared in the July 2016 print edition of The Plaid Horse.

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