By Dr Vicki Glasgow

Of all the basic dietary requirements water is the single most important nutrient. A horse can survive 25 days without feed but only 5 days without water. It is essential for all bodily functions; digestion, waste elimination and body temperature regulation to name but a few. The horse’s body is made up of 70% water so it is not difficult to understand why it is so crucial.

Requirements

Water requirements of the horse are very difficult to predict as the amount required for each individual is influenced by so many outside factors. The type of forage that a horse is provided with can have a large influence on its daily intake. The moisture content of growing (grazed) grass will be in the region of 80%, so a horse living mainly on grass, during the growing season, will require very little extra water. Dry forages such as hay will greatly increase water consumption as will dry feeds (chaffs, nuts and coarse-mixes). Estimates have been made of 10-20 gallons per day for an adult horse at rest or in light work. Obviously, the weather and the amount and type of work a horse does have a very real impact on the amount of water required.

Summer Heat

Total water required increases dramatically when horses sweat due to high temperatures and humidity. We have all had incidences of our horses sweating while they are doing very little in the field on a hot day (even in the UK!) Horses and humans are very similar in this respect in that their primary mechanism for cooling down is sweating. Evaporation of sweat from the skin has a cooling effect and is a very efficient method of cooling. The horse is only able to sweat proficiently if s/he has a level of hydration to allow it. Add work to this equation and water intake suddenly becomes a major issue. When working the horse has to use up energy stores in the body and this process produces heat. The combination of a high work load (producing heat) and high temperature will result in large fluid losses and pose problems for effective cooling. This is why we need to help the horse in these situations by sponging them down with cool water to increase evaporation. Water intake in these situations is absolutely essential to prevent dehydration.

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 who have tried to get their horse to drink at a show, on a scorchingly hot day, with no success. 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 will help,

also mixing feed with water is a good way to improve water intake. Some horses even have a preference for a certain bucket, or colour of bucket, for their water. 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. Top level endurance riders use large amounts of electrolytes to ensure that water intake is optimised; this should only be done by experienced people and for horses that are doing very heavy work. The subject of electrolyte use during long distance endurance races would take up a whole article on its own.

Electrolytes

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.

The problem of electrolyte losses incurred during sweating is compounded by the fact that when a horse sweats the electrolyte levels are more concentrated than the electrolyte levels in its circulating fluids (conversely, in humans, sweat is less concentrated). 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. This can be supplied by providing the horse with a free-access salt block (sodium chloride) or you may wish to add a tablespoon of salt spread over the number of feeds it receives per day. One third of the salt can be replaced with Lite salt (potassium chloride) if the horse is working at a light-medium level but 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, and ironically decrease the thirst response to dehydration. 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).

(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 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). Use the above table to check that the product will replenish electolytes when used at the recommended level. You will be amazed that there are many that do not. 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. Long distance endurance competitors will use paste before, during and after a race but this method should only be used by those with experience or under supervision and for horses in this situation. If the horse doesn’t drink water in conjunction with the paste the problem of dehydration is only compounded as water is pulled in to the gut to dilute the electrolytes there-in.

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.