Electrolytes are minerals found in the horse’s body that carry an electrical charge. Electrolytes are important for a range of functions, including nerve signalling, muscle contraction and fluid balance.
Key electrolyte minerals include sodium, chloride, potassium, magnesium, and calcium.  Ensuring your horse has balanced electrolyte levels can support optimal performance, recovery after exercise, and promote hydration.
Your horse needs to obtain electrolytes from their diet to replenish the electrolytes lost in sweat, urine, and other bodily functions.
Horses at maintenance or in cool climates typically get adequate levels of electrolytes from their forage, except sodium. For these horses, adding plain salt is typically sufficient to balance electrolyte requirements.
Horses in heavy exercise or horses in hot climates can sweat profusely and lose large amounts of electrolytes. If these electrolytes are not replaced through supplementation, these horses can experience exercise intolerance, muscle weakness, and dehydration.
This article will review the function of electrolytes in the horse’s body, the effects on dehydration and performance and how to best supplement electrolytes in the equine diet.
Electrolytes for Your Horse
Electrolytes are minerals that carry an electric charge when dissolved in a liquid. Electrolytes are found in blood, within cells and in the fluid surrounding cells (interstitial fluid).
These minerals are vital for most bodily functions, including nerve transmission, the movement of muscles, and regulating blood pH and fluid balance.
Horses lose electrolytes through drooling, respiration, urinating, defecating, and sweating. These minerals must be replaced by dietary sources to maintain overall health and prevent dehydration.
Electrolyte loss via sweating during prolonged exercise may not be adequately replaced through feeds.  In these cases, supplementing your horse with an electrolyte formulated for equine athletes is recommended.
The most important electrolytes in mammals, including horses, are:
- Sodium (Na+): The most abundant electrolyte in the blood serum, sodium maintains hydration and fluid volume within the body. In horses, sodium is necessary for regulating thirst. 
- Chloride (Cl-): The second most prevalent electrolyte in the blood serum, chloride regulates fluid and pH balance in the body. 
- Potassium (K+): Plays a key role in maintaining cell function and is required for muscle contraction and relaxation 
- Magnesium (Mg2+): Necessary for muscle relaxation and nerve function 
- Calcium (Ca2+): Essential for muscle contraction and nerve function 
Electrolyte Loss in Horses
The most significant loss of electrolytes occurs during sweating. However, illness can also lead to electrolyte loss that needs to be addressed through supplementation or infusion.
Sweating is the primary mechanism by which horses regulate their body temperature. A significant amount of water and electrolytes are removed from their body via sweating during exercise and in hot weather.
Horses can produce up to 15 L of sweat per hour during moderate exercise. Sweat volume and composition will vary according to the intensity of exercise, ambient temperature, humidity, diet, and adaptive response to the environment. 
Based on one study, an hour of sweating at a rate of 15L per hour produces the following electrolyte losses: 
- 105 grams of chloride
- 60 grams of sodium
- 30 grams of potassium
- 4.5 grams of calcium
- 1.5 grams of magnesium
When sweating is excessive, heat exhaustion and dehydration can result in fatigue and poor performance. In severe cases, dehydration can be fatal.
Illness such as diarrhea or other conditions that cause excessive or prolonged fluid loss can disrupt electrolyte balance.
A study of horses with induced diarrhea determined that sodium loss primarily occurs in the feces, whereas urine is the main route for potassium loss. 
Horses with prolonged diarrhea or other gut health issues such as leaky gut should be examined by a veterinarian to determine whether electrolyte supplementation or infusion are necessary.
Electrolytes and Dehydration
Equine sweat is composed of water and electrolytes. Your horse’s sweat is hypertonic, meaning it contains a higher concentration of electrolytes than their blood. 
Losing electrolytes in sweat draws out water. Therefore, with prolonged sweating, horses are vulnerable to dehydration. 
In hot weather, mild dehydration can occur after only a short bout of moderate-intensity exercise and continue for up to 30 minutes into recovery. 
Excessive loss of electrolytes and water decreases the concentration of electrolytes in the blood and other bodily fluids. Counterintuitively, this can decrease their thirst.
Sodium is an important part of triggering a thirst response in the brain. However, if sodium concentration is too low, thirst may not be adequately stimulated to increase water intake and the risk for dehydration increases.
Mild dehydration can result in a range of physiological problems in affected horses, including decreased skin elasticity and sticky mucous membranes.
As little as 1% dehydration from excessive sweating can negatively impact your horse’s performance. Horses are considered clinically dehydrated when they lose 5% of total body fluid (approximately 20-25 L for the average horse). 
Signs of Dehydration in Horses
The signs of dehydration can be subtle but can escalate rapidly if fluid and electrolyte balance is not restored.
Common signs that your horse is dehydrated include:
- Loss of skin elasticity
- Dark-coloured gums
- Stumbling or tripping
- Slower recovery time after exercise (a prolonged elevated heart rate and rapid breathing)
- Slower capillary refill time
- Change in posture or demeanour
- Concentrated (dark-coloured urine) and infrequent urination
In hot weather, dehydration makes your horse more susceptible to heat stress which can result in colic, kidney failure, and death.
Can Electrolytes Improve Performance?
Preloading horses with electrolytes one hour before strenuous exercise has been shown to improve performance, including: 
- Improved hydration levels
- Preventing fluid loss around cells
- Increasing exercise duration
- Increasing fluid and electrolyte loss in sweat when not exercising at peak exertion
Improved hydration levels and enhanced sweating help to lower the core body temperature of horses during exercise.
Horses that receive electrolytes in advance of exercise may be able to exercise for longer than those provided with water alone. 
If your horse is dehydrated and not able to sweat to cool themselves down, they will stop voluntary exercise when their core body temperature exceeds 42oC / 107oF. 
After prolonged sweating, it takes longer for horses to recover a normal hydration status when fed feed and water alone compared to horses provided with electrolyte replenishment.
One study found that horses provided with their normal meals and access to water had an incomplete hydration status 24 h after exercise. 
To fully rehydrate during exercise recovery, your horse should drink the equivalent of 150% of the volume of body weight lost through sweating.
Does My Horse Need an Electrolyte Supplement?
Whether your horse needs an electrolyte supplement depends on factors including health status, activity level, and environment.
Feeding a balanced forage-based diet will supply high levels of minerals including potassium, magnesium, calcium, and phosphorus.
However, forage does not usually provide adequate levels of sodium and up to 70% of horses are deficient in sodium. All horses should be provided with salt in their diet and given access to free-choice loose salt to meet their daily sodium needs.
Research in athletic horses has shown that while many horses are good at self-regulating their salt intake, some horses will not consume enough salt to meet their requirements on their own. 
Providing one to two tablespoons of salt in the feed as well as free-choice loose salt will meet the needs of most horses.
In addition to the electrolytes found in your horse’s feed, a commercial electrolyte supplement can be beneficial when your horse is:
- Sweating heavily
- Working in hot or humid conditions
- Under high-stress conditions, such as long trailer rides
- Working harder and/or longer than they are accustomed to
- Experiencing abnormal fluid loss due to illness
How to Use Electrolytes
There is a wide range of commercially formulated electrolyte supplements available. Check product labels and follow the manufacturer’s directions for proper dosing and administration for the product you are using.
Ideally, electrolytes should be mixed into your horse’s water to promote hydration. Your horse should have an option between two buckets of water: one with the electrolytes and the other with clean fresh water.
Once ingested, most electrolytes are absorbed in the first segment of the small intestine (duodenum). This means oral electrolytes can quickly replenish body levels. 
Electrolytes can also be provided as a top dress on feed if your horse is not at risk for dehydration.
Some electrolyte products are available in a paste format that can be administered via syringing directly into the mouth. However, electrolyte paste products can increase the risk of gastric ulcers.
Furthermore, the high dose of concentrated electrolytes reaching the gut can worsen dehydration in the short term. If using a syringe to administer electrolytes, be sure to make water freely available to drink.
Training your horse to drink electrolytes in water may take time and patience, but it can help to promote water intake in new environments.
Some electrolytes add flavour to the water. This means you can make any water taste the same as their home water if using a flavoured electrolyte product.
Timing & Dosage
The best timing of electrolyte supplementation depends on the stressor that is taking place.
The benefits of electrolyte administration prior to exercise (preloading) are most apparent in sports such as thoroughbred and harness racing, endurance trials, and three-day eventing.
Preloading with 8 litres (2.1 gallons) of water containing balanced electrolytes results in these minerals being present in muscle cells one hour later. 
Administering electrolytes in even 3 L of water one hour before lengthy travel, competition, or any strenuous exercise can support hydration and performance when sweating is prolonged. 
If your horse is sweating while being exercised for under one hour, you can provide electrolytes in their water afterwards or top-dress their ration.
Too Much Electrolytes
Electrolytes are typically underfed as opposed to being over-supplemented. When following the manufacturer’s directions, feeding too much electrolytes is unlikely.
However, excessive drinking and urination can be signs of over-supplementing electrolytes. Excess electrolytes will be cleared from the body through urine.
Safe Electrolyte Replenishment in Horses
Dehydrated horses must be rehydrated with an appropriate balance of water and electrolytes. Isotonic solutions are ideal as they contain water and electrolytes in the same concentrations as sweat or plasma. 
Hypertonic solutions contain a higher concentration of electrolytes than bodily fluids and promote fluid to be drawn out of circulation and moved into the intestine. Administering hypertonic solutions containing concentrated electrolytes (without sufficient water) to a dehydrated horse can worsen dehydration.
Giving only a hypotonic solution (such as water without electrolytes) to a dehydrated horse can also worsen dehydration as it contains a lower concentration of electrolytes than what is normally present within the body fluid.
These solutions dilute the body’s fluids, decreasing the concentration of sodium in the blood and inhibiting the thirst response.
Furthermore, when the kidneys detect lower electrolytes concentration, they increasing urine production, potentially leading to dehydration. 
Feeding Electrolytes to your Horse
To replenish your horse’s sodium levels, plain table salt from the grocery store or feed-grade salt from the feed store is best. Trace mineralized salts can throw off balance in the rest of the diet.
Performance horses consume anywhere between 0 to 62 mg of sodium per kg of bodyweight per day, ie up to 31 grams of sodium for a 500 kg / 1100 lb horse. This equates to ~ 80 grams of salt (NaCl) per day. 
Salt consumption increases when free choice salt is accessible.  In addition, horses drink more water when given access to free-choice, loose salt than a salt block.
Best Electrolyte Supplements for Horses
For horses that are sweating heavily or require electrolyte supplementation due to illness, choose a supplement that is:
- Balanced for horses: Use an electrolyte supplement that is formulated for the needs of horses. Avoid using products designed for humans as horses produce sweat that contains a greater concentration of electrolytes than humans.
- Easily dissolved in water: Electrolyte supplements should easily dissolve in water. If the product is not readily dissolvable, it may not be consumed at adequate levels and may take longer to absorb in the gut.
- Formulated with dextrose or fructose: Electrolyte supplements containing carbohydrate sources such as dextrose or fructose improve the speed at which water and electrolytes are absorbed in the digestive tract. Fructose may serve a similar role in promoting the absorption of potassium (K+). 
Dextrose, a source of glucose, can also replenish energy stores (glycogen) in the body, helping to support exercise recovery.
Mad Barn’s Performance XL: Electrolytes has been scientifically formulated to replace exactly what the horse loses through sweat during heat stress or strenuous exercise. It contains a precise blend of electrolytes, dextrose and vitamins to support high performance and workout recovery.
Performance XL also contains vitamin E and vitamin C, which are important antioxidants that support muscle recovery in exercising horses.
Is Your Horse's Diet Missing Anything?
Identify gaps in your horse's nutrition program to optimize their well-being.
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