Electrolytes (body salts) play a vital role in a horse’s body, helping to maintain the correct balance of fluid in the body and enabling muscle contraction, nerve function and digestion. These substances, which include sodium, potassium, chloride, calcium and magnesium, are found dissolved in the blood and various tissues. Once combined with another electrically charged atom, an ion, an electrolyte produces a salt such as sodium chloride, which drives the body’s essential processes.
Sodium plays an important role in the regulation of thirst. This is the electrolyte that horses tend to be deficient in, as grass and hay are low in sodium.
An electrolyte deficiency can manifest itself in various ways. One of the common yet frequently overlooked signs is poor performance: a small deficit in electrolyte levels can result in subtle signs of dehydration, affecting muscle and nerve function, leaving the horse athletically below par. Other, less subtle signs include dark urine, sunken eyes, listlessness and poor recovery from exercise.
In more extreme cases, exertional rhabdomyolysis (also known as azoturia, or tying up) may be linked. A condition called synchronous diaphragmatic flutter, or “thumps”, can also occur, producing hiccup-like contractions of the diaphragm.
Electrolyte deficiency, or imbalance, has been known to take days, weeks or sometimes months to correct. During deficiency, the horse’s body will attempt to maintain normal levels in the blood by removing electrolytes from other sources, such as bone.
Therefore, taking a single blood sample to check electrolyte levels is misleading, unless the horse is very sick. Paired samples of both blood and urine, taken two weeks apart, can help to monitor electrolyte levels in the high-performance horse, or those with an issue caused by an electrolyte imbalance.
A sticky situation
A horse loses electrolytes even while grazing in the field, via urine, faeces and breath, but they are largely replaced in what he ingests when on a balanced diet. Salt and other electrolytes are supplemented within some feeds, so it is always best to check.
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If your horse does little more than the occasional hack, he is unlikely to need electrolyte supplementation — but horses in moderate to hard work will.
As a horse sweats, electrolytes are lost along with the evaporating fluid — a horse can lose an average of 10g per litre of sweat, with at least 3g of this being sodium. When working moderately hard in warm weather, a horse produces around five litres of sweat per hour — that equates to losing 50g of electrolytes, of which 15-20g is sodium — so may require supplementation with electrolytes. To do this, add them to his feed. If you add electrolytes to water, any change in taste can discourage a horse from drinking. It is also difficult to monitor intake if electrolytes are dissolved in water.
There is a wide range of commercially made electrolyte supplements for horses, but check the ingredients carefully. Aim for a supplement with less than 5% sugar and a high sodium content, with minimal added extras. While sugar is not necessary for optimal absorption of electrolytes, and is not ideal for many horses, it can improve palatability for the fussy eater.
The amount of sodium (Na) and potassium (K) in the supplement should roughly equal the total chloride (Cl), to mimic what is lost in sweat. If you compete, check that any product used contains no banned substances.
It is important that electrolytes are given daily. Adding them to the horse’s feed the night before an event is too late. Not only is a horse more likely to refuse to eat before a competition if he is unfamiliar with the taste of added electrolytes, but feeding them as a one-off or higher dose can create health issues.
Just as a deficiency can result in digestion problems, a sudden loading of electrolytes can cause disturbances of the hindgut. Therefore, it’s sensible to consult your vet before adding electrolyte supplementation to your horse’s diet.
Water works
Ensure that a clean, fresh supply of drinking water is available at all times, especially if you are adding electrolyte supplements to your horse’s feed.
An average horse in moderate work, in warm temperatures, should be drinking around 30 litres of water every 24 hours. If he is drinking a lot more than this, and producing more urine than normal, the electrolyte intake may be too high — a horse can store a certain level in his body, but not an excess. Over-supplementation is very rare, however, and deficiency more common.
Electrolytes are required, in combination with water, to hold water in the cells. When water is lost from the body, sodium levels increase — activating the thirst regulator. If the horse then drinks, but only replenishes the lost water, the levels of sodium will be diluted — although he will no longer have the desire to drink, he will now be electrolyte deficient.
Eating and drinking
A horse may refuse to drink during a competition, or while staying away, so encourage him by taking water from home that has a known taste — or add a small amount of apple juice to the bucket or offer the water left over from soaked sugar beet. By experimenting at home, you’ll find ways to tempt him.
If your horse prefers to drink from his field’s water trough once turned out, offer water from a bucket straight after exercise to familiarise him with the idea of drinking wherever he stands. If he stops eating during a competition, try using an electrolyte paste. Ensure that the paste delivers at least 20g of electrolytes in a single dose.
A small amount of table salt (sodium chloride) added to the feed may be sufficient for a horse in very light work (see guide, right). It is more difficult to judge intake if salt is provided ad lib, in the form of a salt lick or block.
If you use table salt, one tablespoon is about 25g. Offering 1-2 tablespoons daily will help replace sodium and chloride lost during moderate exercise during cooler months. For horses in harder work, particularly in warmer temperatures when sweating is profuse, a balanced electrolyte supplement is a better option, but do check with your own vet.
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