Hot Work – Don’t Forget the Electrolytes

26 Jul 2017

Summer time and excess heat can be particularly hard on our equine friends.  This summer we have had some very hot days and many of you will have been competing in this weather. Some of the more native types have even been wilting and sweating in the field doing nothing. I have had more queries about lethargy this year than usual and a lot of it is down to electrolyte supply. Horses, like humans, use sweating and evaporative heat losses as the main means of cooling down.




When a horse sweats it doesn’t just lose water, it also loses a large amount of salts, or electrolytes. The three main electrolytes lost during sweating are sodium, potassium and chloride with some magnesium and calcium also being lost. Electrolytes carry an electrical charge, which enables them to transfer water through cell membranes (in or out). Thus their main function is to get the nutrients in to cells and the waste out.  They are responsible for the correct functioning of muscles and nerves.   It is also crucial that they are present in the correct balance for these chemical reactions to proceed.

Large electrolyte losses will result in complications such as muscle cramping, tying up, thumps and alkalosis. Sodium is also required as a trigger to the horse to drink. If a horse is low in electrolytes then the trigger to drink won’t be there which could obviously become a dangerous cycle.


The problem of electrolyte losses incurred during sweating is compounded by the fact that when a horse sweats the electrolyte levels in the sweat are more concentrated than the electrolyte levels in its circulating fluids.  This means that not only are water and electrolyte reserves depleted during sweating but body fluids also become out of balance.  This loss of electrolytes and water needs to be replaced and in the quantities of which it was lost.  Obviously a horse at rest or in light work is not going to sweat as much as a horse in hard work but it will still require some electrolyte supplementation especially in hot weather. This can be supplied by providing the horse with a free-access salt block and by adding a tablespoon of table salt (sodium chloride) to its feed. The majority of horse feeds don’t contain enough salt for your horse so it must be provided as an extra.  For horses that are in light-medium work and especially if they have been sweating a lot, a third of the salt can be replaced with Lite salt (contains potassium chloride).  Ordinary table salt is perfectly adequate for idle horses or those in light work, as forage and feed would contain appropriate levels of potassium.


Hot Work


For horses in hard work and in particular in hot weather, electrolyte losses are significant. Excessive losses result in muscle weakness and fatigue.  Electrolyte supplementation must be able to replenish what has been lost to prevent these problems. Research carried out at the Kentucky Research Institute shows the anticipated losses of electrolytes at different levels of work (see table).



At Rest

5 Litres

(Low Intensity)

10 Litres

(Medium Intensity)

20 Litres

(High Intensity)

















(From; Pagan, Kentucky Equine Research Institute. Feeding Management of Horses under Stressful Conditions)


At the 1996 Olympic games in Atlanta horses lost an average of 18.4kg of bodyweight just during the speed and endurance phase of the 3 day event. This equates to a sweat loss of 15 litres.


Electrolyte Supplementation


It therefore is obvious that large amounts of electrolyte minerals and water must be supplied daily to horses doing long distance work, eventing at higher levels, sweating heavily, and in hot humid conditions. This should be provided by using a good quality electrolyte supplement. Look for high levels of sodium, chloride and potassium and that it doesn’t contain cheap fillers or very high levels of sugars (some sugar is fine to encourage intake). Most proprietary electrolytes don’t contain anywhere near enough sodium so continue to use table salt and top up with the “fancy” electrolytes.  Unfortunately horses do not store electrolytes from one day to the next, so “loading” electrolytes for days before competition is of little value and will just increase urine losses. It is advisable to give an electrolyte supplement a couple of days before an anticipated strenuous competition, during it and for a couple of days after.  In the majority of cases the electrolyte supplement should be provided in the feed to prevent negative effects on water intake if it is added to water buckets.


Water Intake


You can lead a horse to water…but you can’t make it drink. I am sure that this old adage will ring true with many people. There are some tricks used by top event and endurance riders which will hopefully assist you in keeping your horses hydration levels up at shows this summer. The favourite one is to take along really sloppy sugar beet or just the juice. Most horses will be tempted by this one. Another idea is to flavour your horses water at home with apple cordial, or peppermint (whichever works) a few days before the competition and then use the flavouring when you are at the competition. Feeding soaked hay or haylage will help, also mixing feed with water is a good way to improve water intake. A high fibre/forage based diet helps with water reserves as the fibre in the horses gut holds a lot of water and research has shown that 20 litres of water can be drawn from the gut to help replenish body fluid levels.  Crucially, remember to always allow your horse access to clean, fresh water.

In summary it is very important to consider your horse’s water intake and electrolyte needs during the hotter weather. Salt supply on a daily basis will fulfil the needs of the majority of horses during training and normal activity. A good quality electrolyte supplement should be added to the horses feed for a day or two if it has sweated heavily during training or at a one day show.  For competitions which extend over a number of days at a high intensity (e.g. 2 or 3 day events, long distance endurance races), electrolytes should be provided a couple of days before the event, during the competition and for a couple of days after.

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