Electrolytes are required for almost all bodily functions including nerve function, digestion and muscle contraction. Electrolytes such as calcium also play a central role in ensuring adequate bone strength. It is very common for horses not to be receiving enough electrolytes, especially sodium. Electrolyte deficiency and imbalance usually takes weeks or months to become a problem and can take weeks or months to correct. Signs of electrolyte deficiency or imbalance can include poor performance, slow recovery after exercise, muscle problems (such as tying-up), reduced sweating, increased risk of fracture and “thumps” (which is most common in endurance horses but can occur in any horse). It is very unusual for horses to be fed too much electrolyte, provided you stick to manufacturers’ recommendations. Signs that you are feeding too much electrolyte could include feed refusal, excessive drinking (more than four buckets per day), a very wet bed and/or loose droppings. But over-supplementation is very rare in my experience!
Why electrolytes are essential for horses
The major electrolytes are sodium, potassium, chloride, calcium and magnesium. Many electrolytes exist as mixtures of more than one electrolyte. For example, sodium chloride is more commonly known as table salt, which is a compound of sodium and chloride, denoted by the chemical formula: NaCl (Na = sodium and Cl = chloride). Electrolytes are necessary for urine production and so are lost on a daily basis in urine, as well as in faeces. If a horse is exercising, then electrolytes are also lost in sweat – around 9g in total of sodium, potassium, chloride, calcium and magnesium in each litre of sweat. Hard feeds and forage do contain electrolytes but will usually not replace what a horse in more than light work uses up each day. Horse diets in particular are usually deficient in sodium. Forages (grass, hay, haylage) are low in sodium. Sodium is also the most important electrolyte when it comes to regulation of thirst. It is ok to provide your horse with a salt lick in its stable or pasture, but chances are it will not use it to correctly address its salt needs. Four separate scientific studies have shown that horses DO NOT regulate their salt (sodium chloride/NaCl) consumption to match their needs from free choice salt when provided in the form of blocks or licks.
Managing electrolyte consumption of your horse
The best strategy for feeding electrolytes is to feed the same amount every day. Allow the horse’s kidneys to work out what it needs, and it can excrete what it doesn’t. As opposed to just feeding on harder work days or when competing. It is a myth that horses cannot store electrolytes in the body, so you cannot and should not try to “load” horses by giving them a large amount of electrolytes on the day of a competition. This will not correct a long-term deficiency and you risk putting the horse off its feed and/or upsetting the hindgut, and the horse will simply excrete the majority in faeces and urine. It is a myth that sugar (glucose, dextrose) is required for optimal electrolyte uptake from the stomach. Sugar is included to make electrolytes palatable but it has no other function. Blood electrolyte levels are a very poor indicator of electrolyte status except in the case of sick or very deficient horses. The body attempts to maintain “normal” blood levels even if the levels in tissues and organs are very low. For example, the blood calcium level may be normal because the horse is breaking down bone to maintain the blood levels, which in the long term can increase the risk of a fracture.
The only sure way to know exactly if you have your electrolytes right is to do a full diet analysis and then ask your vet to collect paired blood and urine samples. You can then tailor your electrolyte management for each individual horse. You will probably need to repeat this over two or three months. This is usually only required for high-performance horses, horses that don’t respond normally to supplementation, or horses with ongoing problems such as tying-up.
An excess of electrolytes
Excessive feeding of electrolytes can increase water intake and may also lead to gastric ulceration, worsening of ulcers if they are already present, and hindgut disturbance (loose droppings to scouring). But, in my experience this is very rare and most horses are likely to be under supplemented. An excess could be supplementing more than 100g per day in cool months when the horse is in light work, or more than 200g per day in the summer when the horse is in hard work. It is much better to feed a slight excess of electrolytes and allow the horse to regulate what it needs by excreting what it doesn’t need. This of course requires sufficient water to be available. If you feed too little electrolyte on a daily basis the horse will try to conserve electrolytes, but it can only do this for so long. Eventually an imbalance will occur and the “normal” levels will not be able to be maintained.
Electrolytes for a horse that isn’t drinking
It is commonly advised not to give electrolytes to a horse that isn’t drinking – but this is a myth! If a horse has worked hard and has lost a lot of electrolytes in sweat, then if they are not drinking, this is not a good sign. If they continue not to drink, this can increase the risk of colic. Giving a concentrated electrolyte paste may stimulate a horse to drink and is safe provided they have access to water. It is often said that electrolytes draw water into the stomach and therefore they should not be given, but this is actually the physiological process that stimulates the horses thirst mechanism.
Horses with gastric ulcers
For a horse with gastric ulcers or a history of gastric ulcers, the use of ordinary electrolytes may cause appetite and thirst suppression, pain and discomfort, and lead to the worsening of existing ulcers and development of new ulcers – think of rubbing salt in a wound! For these horses feeding a fat-coated electrolyte will be particularly beneficial. The fat coating is not dissolved by the stomach acid but only by enzymes called lipases in the alkaline environment of the small intestine – the main site of electrolyte uptake.
Supplementing around a competition
Supplementing only around the time of competition, or changing how you supplement around the time of competition, will probably be considered undesirable for two main reasons:
- Firstly, a negative effect on palatability of the feed. If your horse is not used to the taste of salt in their feed, then supplementing before a competition could put your horse off eating.
- Secondly, you are highly unlikely to have much impact on whole body electrolyte status by starting to feed electrolytes, or feeding extra electrolytes, around the time of or during a competition. There is also the risk that a sudden increase or change in electrolyte supplementation around the time of a competition could cause disturbance to the hindgut.
What a horse needs in terms of electrolytes will be determined by a combination of diet, work, breed, fitness, weather and factors peculiar to your individual horse’s metabolism.
Key points regarding electrolytes and horses
- Electrolyte deficiency and/or imbalance is a common cause of poor performance and may increase the risk of problems such as tying-up.
- Most horses will benefit from 1 × 25ml (around 25g) of ordinary table salt in their feed each day to ensure sufficient sodium intake.
- Some feed companies, including The Pure Feed Company, do add some salt to their feeds.
- Do not rely on salt blocks to meet a horse’s salt or electrolyte needs.
- If your horse is in work, then the addition of a balanced electrolyte on a daily basis is recommended.
by Dr David Marlin, Pure Feed Nutritional Consultant