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Also Known As

Lack of water, Thirst


Long rides and vigorous exercise on hot, humid days often create demands for hydration that a horse's body cannot meet. Sweating is the body's way of getting rid of excess heat, and, when the body becomes dehydrated from too much activity, coupled with sweating, it loses necessary reserves of fluids and electrolytes, which can lead to heat exhaustion or stroke and possibly death. .

Most adult horses weighing around 1,000 pounds require a minimum of 10 to 12 gallons of water each day for their basic physiological needs. Water is an important nutrient that is needed for almost every bodily function. It helps maintain digestion, moisture level in urine and feces, normal blood volume, and aids in the regular functioning of sweat glands.

Dehydration and loss of electrolytes can result in neuromuscular and systemic imbalances that threaten both the health and life of the horse.


  • Fails pinch test (When skin is pinched near base of the horse's neck for 2 seconds, then released, it should return to normal immediately.)
  • Sluggish activity and loss of glossy coat
  • Muscle spasms and signs of pain
  • Lack of saliva resulting in decreased feed intake
  • Impaction colic or constipation
  • Cardiac arrhythmias
  • Fatigue
  • Depression


Evaporation is the main way a horse gets rid of heat built up through activity. The horse's physiological efficiency may then become compromised when excess activity, particularly during warm weather, leads to excess evaporation and resulting dehydration. Sweating at an acceptable level can occur only when a horse is fully hydrated and has plenty of fluids in the body to maintain bodily functions, as well as regulate temperature through evaporation off the skin surface.

Prolonged maximum exertion, such as endurance riding, especially on hot, humid days without proper attention to the need for plenty of good, clean water, and salts (commonly referred to as electrolytes), will cause the horse's body to become stressed, leading to a variety of physiological problems, including poor heart and respiratory responses, kidney impairment, muscle spasms, heart arrhythmias, gastrointestinal stasis, fatigue, and reduced muscle function.

A trotting horse loses about 3.3 gallons of sweat per hour under moderate conditions. The salts -- including sodium, potassium, chloride, magnesium and calcium -- are also lost along with the loss of fluid. These salts/electrolytes are responsible for the transfer of water through cell membranes that keep the system of the horse working properly.

In some areas, the cold winter months bring additional problems with dehydration because cold weather may greatly reduce the horse's thirst, especially if the humidity is high. Some horses will eat snow, but horse owners should not consider snow as a water source.

Because water is also lost through the saliva it takes to soften food, through urine and feces, as well as through the moisture in the horse's breath, the animal needs to have access to adequate amounts of water on even the coldest days. .


The first and most important step in preventing dehydration is paying attention to each horse's consumption of water. Some horses can get by with five or six gallons of water a day, but since a three to four percent loss of body water will cause mild dehydration, most horses require a minimum of ten to twelve gallons of water per day.

In addition to water, the horse's body requires electrolytes for biochemical reactions within the body to get nutrients in and waste products out. Electrolytes are responsible for nerves functioning properly and muscles contracting properly. If a horse sweats out these electrolytes in too large amounts, balance is not maintained, and the horse's ability to endure is greatly compromised.

Many times, horses could do much better if handlers and owners paid attention to making sure electrolytes and fluids are balanced and at appropriate levels for the weather and the activity.

Never riding or exercising a horse to the point of exhaustion is another way of preventing dehydration. Forcing a horse to be active in hot, humid weather almost insures dehydration and electrolyte imbalance.

Wise timing of exercise by taking advantage of cool periods during the day and making sure the horse has time to drink and has access to salt during the activity will keep the horse safe from the consequences of prolonged periods of dehydration.

Check for signs of dehydration regularly and don't wait until a horse looks dehydrated to administer electrolytes. Learn to perform skin pinch and mucous membrane testing and how to listen for gastric sounds to help determine when a horse is becoming dehydrated.


Access to plenty of clean water with the opportunity to drink any time the horse is thirsty, plus monitoring how much the horse is drinking, will help keep the horse properly hydrated. In cold weather, warming the water to a temperature around 90 degrees helps encourage horses to drink sufficient amounts.

Increasing salt intake will also stimulate a horse to drink more. A 1,000 pound horse should be consuming about two ounces of salt per day, and salt should be available at all times.

Feeding a well-formulated commercial ration intended for the level of activity of the horse will help prevent electrolyte imbalance and help enhance hydration.

If a horse becomes severely dehydrated, the introduction of warm water to the stomach by tube or intravenous rehydration may be necessary. Adding extra water to mash, and letting it sit for 10 minutes to permit expansion of the grain will also help with water intake. .

The good news is that, given the opportunity to drink and the availability of sufficient fresh water, most horses will not suffer from dehydration.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.