Water and Electrolytes

As water is the main constituent of every horse, human or indeed any other animal, it should go without saying that the horse should have free access to water. But how much further should we take this? Clean water? Sterile water? Pure, demineralised water?
Well, obviously the first one, unless you like vets bills! But the second or the third? That's a bit extreme, and the trace amounts of other things in the water won't do the horse any harm and may even do him some good.

You might be surprised to learn that even a slight drop in a horse's hydration levels can cause a significant drop in performance, especially stamina and recovery rates. It also reduces a horse's ability fight off disease. A total lack of water is much more quickly fatal to a horse than a lack of feed.

Water is lost from the body through excretion (urine and faeces), breathing, sweat and evaporation, and during lactation in mares. Water must be consumed to maintain the fluid balance, for the gut to work efficiently, and for gut health. So how much water and when? Well, the short answer is as much as he wants and when he wants it. But it isn't quite that straight forwards...
If your horse is going to be doing fast work (racing or going cross county) then he doesn't need a belly full of water sloshing about, so restricting water intake for half an hour before the start is a good idea as long as the horse has had opportunity to drink his fill up until that point.

If your horse has been doing fast work, or been out hunting all day then allowing him to fill himself with cold water on an empty stomach while he's still breathing hard is a recipe for disaster. Walk him round until his breathing is back to something closer to the normal rate. Get him to take a small quantity of water with electrolytes (we'll come onto this in a bit)made up with a bit of warm water to take off the chill. Once he's settled and had a chance to relax he can be allowed to take on as much water as he needs, and probably will end up taking more because he's not over-loading his system in one go.

Keeping a Horse Hydrated
You might think it's as simple as giving him enough water and that's it. But you're not quite on the mark. That's a large part of it, yes, but there's little things that you can do to help him stay hydrated for longer.
1) feed fibre first... the fibre helps to hold water in the gut, releasing back to the bloodstream slowly, helping the horse to stay better hydrated. The more used to having the fibre the horse gets the better able his system is to hold the water within the gut.
2) electrolytes, or access to a salt lick, encourages the horse to drink more - its a natural reflex and once horses get over the novelty of a salt lick they will self-regulate the amount they take.
3) more fibre.... No. seriously!

So what affects how much water your horse needs?
the weather and temperature - a horse will lose more water on a warm windy day than on a cold still day by up to 35%
his work load and the type of work he's doing - a short, gentle hack will obviously be less likely to cause him to drip with sweat than a full blown cross country round unless he's very unfit, although the time might be about the same, the work load and stress on the horse's system is totally different. But equally, an endurance ride even over the greatest distances compared to a day hunting will produce similar amounts of water loss. The timings might be quite different but the work loads and the types of strain on the system are quite similar.
his conformation and muscle mass - a fit arab or thoroughbred has much less muscle mass than an equally fit Irish Draft or Welsh Cob. The heavier types find it much harder to disperse the heat produced during work, largely due to the amount of muscle compared to the surface area. This in turn leads to much greater sweating and water losses.
his health - a horse in poor condition, run down or sick will have a much larger requirement for water as his body tries to cope with the extra demands on his system.
his temperament - excitable horses tend to sweat up more, and have higher respiratory rates than more laid back characters, leading to higher water losses.

Electrolytes

Electrolytes are essential mineral ions required by the body to maintain water balance and also to fuel certain cellular processes including muscle function. The term is often then applied to salt and sugar compounds that are fed to horses to help with rehydration and recovery after heavy water losses and strenuous exercise. In this part we are referring to the latter.

Proprietary Electrolytes and how to use them
firstly - do you need to be using them? using them when you don't need to is money down the drain (or rather, into the muck heap) as they will just get excreted. if the horse has access to a salt lick, and not been working then the chances are he doesn't need electrolytes today.
secondly - you've decided he does need them, so how much should you give him and when? again, it comes down to the work he's doing. For hunting I feed two measures of electrolyte the night before in wet feed, and one in the morning before hunting, and then on return the horses will get two or three measures in two buckets of water on return. But for eventing at Novice level I only use half a measure in water after cross country.
thirdly - how should you give them tot he horse? Generally it it better for the horse to drink them dissolved in water, but not every horse will take them that way. If not then add them to a wet feed. Doing this helps to ensure that the horse starts to take on water, so reducing the chance of causing dehydration.
fourthly - make sure the horse has plenty of clean, fresh water available so that the horse can then take on water as he requires.

Proprietary Electrolytes and what to look for.
Generally speaking, any electrolyte supplement ought to consist of at least 50 percent chloride, 20 percent sodium, 15 percent of potassium, and only about one percent of other trace minerals, such as calcium and magnesium, and some form of sugar.
Firstly look at the basic ingredients of the tub or bottle (I would always recommend a liquid or powder form over a syringe as it's much easier to dehydrate the horse with a syringe as you cannot stimulate the water uptake as easily). The ingredients should be Common Salt (Sodium Chloride), Lo-Salt (Potassium Chloride), glucose or dextrose, Calcium Chloride or Calcium Acetate or Calcium Carbonate (the latter is the least soluble), Magnesium (one of several compounds is possible) and then one or more of the following:
Vitamin E
Citric Acid
flavouring
Vitamin B complexes

The vitamin E, vitamin B complexes and citric acids are all anti-oxidants that help to protect the horse's gut from the salts - too much salt without the anti-oxidants has been linked to gastric ulcers.
Vitamin B, and the sugar (fructose, glucose or dextrose) helps to stimulate the horse's gut to start working again, and as these are both water soluble and need to be dissolved for the gut bacteria to use them, it highlights the need for the horse to start taking on water with the electrolytes.
The flavouring just helps to encourage the horse to take the electrolytes dissolved in water or wet feed - it doesn't really matter what the flavour is, though much research suggests that horses prefer cherry or apple flavour to mint.

I hope this is of help, and if you have any questions feel free to ask!