What a spell of hot and dry weather we have had and as I write this, we are still having.

It is usually around now that we start to get queries about general lethargy and under performance in horses. In the majority of cases, this is purely down to a lack of vitamins and trace elements and/or electrolytes in the diet, which is easily solved if you follow the advice below.

There are other issues to look out for as a consequence of this glorious weather, which are also worth bearing in mind as the seasons move on.


Horses sweat to keep cool and can lose copious amounts of fluid as sweat. Even when working at only a low to moderate level of intensity, horses can lose in the order of five litres of sweat per hour!

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.

Hay and feed do contain electrolytes, but not in the quantity required by your horse on a daily basis and most definitely not enough to replace the losses incurred by sweating.

Coarse mixes, cubes and balancers also do not contain enough salt to fulfil your horse’s requirements. This is because there is only so much salt that can be put in to a horse feed and if put in at high levels it starts to become aggressive to the vitamins present in the feed.

Essentially, this means that your horse should always be supplemented with salt.

Salt provision

Most people supply their horse with a salt lick, which is great and to be encouraged, but not all horses will use them.

It would take a horse hours and hours of constant licking to match anywhere near their sodium requirement via this route. It is much more preferable for them to also be given salt in their feed every day so that you know that they have definitely consumed their daily maintenance requirement.

Table salt is sodium chloride and giving your horse one tablespoon of table salt per 250kg of bodyweight each day will ensure their daily requirements for sodium are met. It should be borne in mind that 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.

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)

Sodium 15-20g 33g 50g 85g

Chloride 27-33g 55g 83g 139g

Potassium 40-50g 46g 52g 64g

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

Electrolyte supplementation

It is, therefore, 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. Find an electrolyte that contains high levels of sodium, chloride and potassium preferably a minimum of 12g of chloride, 6g of sodium and 4g of potassium in a measure and that it doesn’t contain cheap fillers or very high levels of sugars (avoid those that have glucose as the top ingredient in the raw material listing).

Most proprietary electrolytes don’t contain anywhere near enough sodium so continue to use table salt/lite salt mix (2-3 Tablespoons per day) and top up with the electrolytes.

Minimise wastage

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.

Be aware

At some point the weather will break and grass that has been deprived of rain for weeks on end will suddenly be watered.

This, in conjunction with heat, will bring about a flush of grass. Please be aware of this and practice good management of any horses and ponies that are prone to laminitis and/or are running a little too fat.

The vets and farriers have already seen a higher than usual incidence of laminitis this year. Don’t let it catch you out.