Horse Water Intake Requirements

Your horse’s body is 70% water. He can survive for a while with no food but only a few days without water. The function of every cell and every biochemical reaction in the body needs water.

Optimal hydration is essential for good performance. It takes 7 mL of water to make 1 gram of energy-giving glycogen stored in the muscle. Even a slight dehydration of 2 to 3% will cause a 10% drop in exercise capacity. Without adequate water, blood circulation, muscle perfusion and function, and the ability to control heat build-up during exercise suffer. Even mild dehydration greatly increases the risk of heat stroke.

Provide More Than Water

Simply providing water is no guarantee the horse will drink enough to stay well-hydrated. Thirst is controlled by centers in the brain called osmoreceptors, which sense the level of sodium in the blood. Sodium is the major osmotically active electrolyte in the blood and extracellular (outside the cell) tissues. This means that it ”holds” water. Where sodium goes, so does water.

When sodium levels in the blood start to increase because of water loss, the brain first releases a hormone called ADH, antidiuretic hormone. This opens special pores in the kidneys that allow it to absorb pure water, rather than sodium and water like it would normally do. This helps dilute the blood sodium back to a normal level. If this isn’t enough to correct the blood, thirst will be triggered.

In the opposite situation, if blood sodium is dropping, the blood will not hold a normal volume of water. This triggers release of the hormone aldosterone from the adrenal gland. Aldosterone makes the kidney reabsorb more sodium, excreting potassium in its place. It’s probably responsible for salt hunger.

Note: Understanding aldosterone explains why many horses with performance problems related to low potassium often don’t respond to potassium supplementation. Dietary potassium deficiency is rare, but most equine diets are low in sodium. The hormonal systems put a high priority on maintaining normal blood sodium levels. If sodium intake is too low, the kidneys will actively excrete potassium and save sodium, even if blood potassium levels drop below normal.

For horses with chronic problems related to low potassium, give more salt/sodium, not more potassium. This is a common mistake made when supplementing performance horses.

Hormonal checks and balances sound like a good system, and they are — but there’s a catch. When the blood levels of sodium or water are low, these will be pulled into the blood from the fluid in the tissues.

Since the blood levels remain normal, the brain will not ”know” the horse is actually dehydrated. Salt hunger and thirst will not kick in. This is an efficient survival mechanism, and a horse not working regularly can get by, but exercise, hot weather or a gut upset could easily put a horse like this into severe dehydration. The solution to maintaining optimal hydration is to guarantee the horse has both access to water and an adequate intake of sodium in the form of salt.

Adequate sodium and optimal hydration go hand in hand. The single best way to keep your horse drinking well and holding onto the water his body needs to perform smoothly is to guarantee an adequate intake of salt.

Adding electrolytes

In an upcoming issue, we’ll review commercial electrolyte supplements, how and when to use them, and how to select one. For now, it’s important to realize that electrolyte supplements alone can’t keep your horse well-hydrated. A common mistake is to assume that because you feed an electrolyte supplement according to label recommendations your horse’s needs will be met.

Electrolyte supplements are designed to provide sodium, potassium and chloride, the major electrolytes lost in sweat, in proportions similar to sweat.

Human sweat contains electrolytes in amounts similar to those in the blood, but equine sweat is different. It has much higher concentrations of potassium and chloride relative to sodium than those found in blood. It certainly makes sense to replace electrolytes lost in sweat in amounts that match sweat but this ignores an important part of the big picture. Are the horse’s water and electrolyte levels optimal before exercise starts’ In other words, is she starting work with a full tank’

In the top table on page 8, we show shows the sodium, potassium and chloride requirements of an 1,100-lb. horse working up to an hour a day at different work intensities. Horses working longer would have higher requirements. It also shows what is present in an unsupplemented 20 lbs. of hay and a suggested dose of a typical electrolyte supplement. Grains contain low levels of these electrolytes.

As you can see, the electrolyte supplements don’t come even close to meeting needs, but that’s OK. They’re not supposed to. What they are supposed to do is help replace sweat losses after the diet is adequate to meet baseline needs. Most electrolyte products have a suggested daily dose that is based on assuming the horse works an hour or less and does not sweat excessively. In the electrolytes supplement article, we’ll explain how to use these. The take-home message in terms of guaranteeing the horse starts the work day with optimal hydration is obviously to supplement sodium — plain salt.

Horses that are picky about water when away from home and don’t drink well can be a real problem. One cause of this is poor salt hunger and poor thirst.

Salt is 40% sodium. On days they aren’t working, average horses need 10 grams of sodium or just under an ounce (2 tablespoons) of salt. In work, the requirement increases to 4 oz./day for horses working at high speeds in very hot weather or as much as an ounce of salt per hour for hard endurance work in the heat.

The electrolytes article will give tips for staying on top of this, but step 1 is to ensure the horse is getting the estimated daily sodium requirement for his level of work. Simply doing this will solve most problem drinkers.

That said, some water sources are either so different from water the horse is used to (e.g., chlorinated water vs. well water), or have strong tastes for other reasons, that some horses just won’t drink them and prefer to wait until they get home to catch up on their needs. They will catch up over a few days, but if you’re away from home and need the horse to keep performing, this isn’t a satisfactory solution.

One method some people use is to add molasses, sweet feeds, brans or another appealing food to the water. This often works, but it has some drawbacks. When using large amounts of these additives, you need to subtract all those calories from the horse’s other meals. It’s also a dream-come-true for bacteria that will begin to ferment these mixtures quickly, so discard water the horse doesn’t consume right away, especially hot water. Also be prepared to scrub these buckets thoroughly to remove food residues.

Bottom Line

There are good drinking-water additives available, and you’ll need to try them to see which your horse might enjoy most. You need to determine if you need a tempter or a masker or both, when it comes to enticing the horse to drink.

The least expensive solutions are to bring water from home or purchase drinking water in a five-gallon jug and bring it with you. In fact, one of the most difficult situations is a horse that will not drink chlorinated water, which you may run into on some showgrounds with ”city” water. For those situations, bring water with you.

Horse Quencher is a commercial product based on the idea of adding food to water. Just remember the precautions about residue and calories if you use this.

EquiTea, from Equine America, was one of the first products of this type. It worked very well for us in a past field trial and remains our favorite.

Uckele’s EquiSweet liquids were not designed for drinking water but could be used that way. It likely has more of an odor-masking than flavoring effect, so may work well for the horse that won’t even taste water that doesn’t smell like his, even if you can’t smell any difference.

To use flavoring or masking strategies, begin by giving the treated water at home. When you find something the horse likes, bring in water from an outside source to make sure it will work with other waters. Don’t use these every day, but offer the treated water for a day or two in advance of your planned trip.

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