What are Electrolytes?
Electrolytes are one of the most abundant compounds in the body after water. The major electrolytes include sodium, potassium, chloride, calcium and magnesium. All compound feeds and forages contain some electrolytes but a grass/hay and/or commercial feed diet will generally only supply adequate amounts of the different electrolytes for horses at pasture or in light work and the one electrolyte that will always be deficient is sodium (salt).
Electrolytes are not evenly distributed throughout the body. For example, potassium is high in red blood cells and nerve cells but low in the plasma. Calcium is low in plasma, but high in bone and muscle cells. When it comes to hydration, sodium is the most important electrolyte. Not all the electrolytes consumed by a horse will be absorbed. However, for major electrolytes like sodium, potassium and chloride the absorption is very high (probably 90% or more).
Why are Electrolytes important for a horse?
Horses at rest lose electrolytes on a daily basis in faeces, urine and breath. During training and competition the event horse will also lose electrolytes through sweating. The harder the horse works, the hotter the horse gets. The longer a horse works and the warmer the weather, the more sweat and therefore the more electrolytes a horse will lose. One litre of horse sweat contains around 3.5g of sodium, 6g of chloride, 1.2g of potassium and 0.1g of calcium. A horse can easily lose 5 litres of sweat each hour on a normal day at a moderate pace which equates to the loss of around 50g of electrolytes. This amount would not be replaced by the horses’ normal daily hay and hard feed alone.
Eventers in regular work need supplemental electrolytes to perform optimally and to avoid problems such as poor performance or digestive disturbance, or clinical problems such as synchronous diaphragmatic flutter (also known as “thumps”; a condition where the chest twitches in time with the heartbeat due to stimulation of the diaphragm) or some forms of tying-up. A diet low in electrolytes is also a common and often undiagnosed cause of horses not performing to expectation.
One common myth about electrolytes is that horses cannot store them. The truth is that they cannot store excess electrolytes. If you suddenly add in a large amount of extra electrolytes into your horses feed, he will drink more as the kidney excretes the excess. However, you can make the horses’ body used to storing higher levels of electrolytes by feeding higher levels over a longer period of time. Another myth is that horses know what electrolytes they need and will take this in from a salt block in the stable or paddock. An increasing number of scientific studies have shown that horses do not regulate their intake from salt blocks. For example, for horses needing perhaps 50g of salt each day, some will take none from a salt lick and other may take in up to 4 times more than they need. Finally, sugar is not needed for electrolytes to be absorbed effectively from the gastro-intestinal tract.
If you are feeding too little, then your horse may perform poorly, especially in warm weather or be prone to high muscle enzymes, tying-up or thumps or have slow heart rate recovery after exercise.
If a horse drinks water alone, this cannot be held in the body and the kidney will try and remove as much of the extra water as possible. If water is taken in with electrolytes, either in feed, given by syringe or dissolved in the water, the water can then be held in the body and the horse will rehydrate. Although horses will drink water with electrolytes in, I would advise strongly to give electrolytes in feed as it is difficult to meet requirements by giving electrolytes in water.
Can I just add normal salt to my horse's feed?
Many people do add ordinary table salt to the horse’s feed but the first question is how much do you add? This will depend on many factors including diet and time of year as well as level of work. There is also the problem that unless the salt is mixed in with the feed and possibly the feed is wetted, the salt can fall to the bottom of the feed bucket and does not get eaten. It is also well known that adding extra salt to the diet can cause problems such as food refusal. Furthermore there is evidence that ordinary salt can cause or worsen gastric ulcers in horses. For eventers in light work, some salt in the daily feed may be adequate. For eventers in more than light work, salt alone is unlikely to replace training and competition losses and a complete balanced electrolyte needs to be provided.
When should I feed Electrolytes?
The simple answer to that is every day! It is common for many event horses to only be fed supplemental electrolytes immediately before and during competition. If you feed enough electrolytes during training you will not need to increase the amount in the feed when it comes to a competition. If you don’t feed in training and feed only in competition you are asking for trouble. It can take weeks or months not days to fully restore the body’s normal electrolyte levels following a month or so of training.
The event horse in work should normally receive most of its electrolytes in its daily feed, from a combination of electrolytes from fibre sources, hard feeds and electrolyte supplements. Supplements should be split between feeds. In circumstances where horses are not eating or where extra electrolyte is required to be administered for example before, during or after training, transport or competition, then electrolyte paste from a syringe is the best option. There is a myth that electrolyte pastes will dehydrate a horse by drawing electrolytes into the stomach and small and large intestines. An electrolyte paste WILL draw water into the GI tract, but this is what will increase the concentration of electrolytes in the blood and this increase is the trigger that will make the horse drink.
When choosing an electrolyte supplement, look for the sodium or sodium chloride (salt) content. The higher the sodium chloride content, generally the better the product. This is usually expressed either as g per dose or %. For an electrolyte powder, the sugar (sometimes shown as dextrose or glucose), this should be low (less than 5% or 5g per 100g or 50g per kg), otherwise you will be feeding a lot of sugar and not enough electrolyte. For electrolyte syringes, a good syringe should be delivering at least 20-30g of electrolyte per dose.
It may be hard to tell if you are under-supplementing your eventer with electrolytes until you have a problem. What about over-supplementation? If you follow the manufacturer’s instructions it is unlikely that you will end up over-supplementing. In my experience it is very rare for event horses to be fed too much electrolyte. It is almost always a case of them being fed too little. But, if you were feeding too much the classic signs to look for would be excess drinking and very wet bedding. Expected water intake for a 500kg horse in moderate work in cool-warm weather is in the region of 25-30 litres per 24h (15 litres is usually around 1 bucket). If the intake is much higher than this (for example 40 or 50 litres) AND the floor is wet, then electrolytes may be overfed. If the intake is high but the floor is NOT wet, then this means the horse is simply replacing what it has lost.
Almost all horses need a small amount of salt on a daily basis
Horses in more than light work require supplemental electrolytes
Electrolytes should be fed according to level of work and weather by following manufacturer’s instructions
Electrolytes should be provided daily for horses in training and not just around times of competing
Do not increase the amount of electrolytes fed as competition approaches. This may cause problems with feed refusal, gastro-intestinal disturbance and simply increase drinking
For effectiveness, look for products high in sodium or salt and which are “balanced” (contain the right amounts of each different electrolyte)
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