As much time as we spend fretting over every other aspect of our horses' lives, few of us pay proper heed to the most important equine need of all: water. Sure, we dutifully fill up their buckets and troughs, but rarely do we consider just how critical that simple molecule is to the horse’s well-being. The reason is simple enough: It's exactly because water is so fundamental to his life–and ours–that we spend so little time thinking about it. After all, the price of water doesn't fluctuate like hay, and there isn't a "new and improved" formula released each year. This product was developed and market-tested long ago. As long as it's readily available and clean, what’s there to worry about?

Fortunately, not much. Still it's worth taking a moment to explore the many compelling, and often surprising, features of water. For instance, did you know that equine body types evolved in direct relation to the availability of water? Or that one particular horse in a wild herd dictates when the rest will drink? Or that about 70 percent of your horse is water? Facts like these may not be earth-shattering, but we think you'll agree they are fascinating. And they just may make you pause the next time you drag the hose to the trough and appreciate how much you, and the water you deliver, are providing to your horse.

Physiology

Consumption

Water Needs

Environment

Physiology of Water

• If you drained all the water from a 1,000-pound horse, you would have removed 70 gallons, and he would weigh a mere 440 pounds.
• Water makes up 65 to 70 percent of the average horse's body. A human body is 65 percent water, an apple 85 percent and a jellyfish 95 percent.
• Water accounts for 85 percent of a horse's brain, 75 percent of his muscle mass and 30 percent of his bone.
• Water bathes and cushions the brain and central nervous system, and lubricates all the body's moving parts. It also plays a critical role in regulating the body’s temperature through sweating.
• Water plays a role in both hearing and vision. The inner ear contains fluid that vibrates in response to sound waves, sending nerve impulses to the brain. The eyeball, which is predominantly water, is continually bathed in fluids from the lachrymal gland.
• The hypothalamus, a gland located at the base of the brain, controls the body's use of water by secreting antidiuretic hormone (ADH). When ADH is released, the cells retain water; when it is suppressed, they release it more freely.
• The body has four main repositories for water:

  Intravascular space	The blood vessels hold about five percent of the horse's total body fluids, a level that is subject to rapid fluctuation as the body's needs change.
  Extracellular space	About 15 percent of the body's water surrounds the blood vessels and cells.
  Intracellular space	Up to 50 percent of the body's water is contained inside the cells. This fluid level is critical to the specialized performance of cells and is less adaptable to change than any other bodily water reservoir. Only about 10 percent of the water in intracellular space can be moved without serious consequences to the horse's health, and it can take two to three days to replace water lost from this area.
  The gut	The remaining 30 percent of water is stored in the large intestine and cecum, providing a holding tank of sorts that's unique to horses. About half of the water in the cecum is available to replenish losses elsewhere in the body.

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Water Consumption

• The equine stomach holds three to four gallons of water, which is as much as a very thirsty horse can drink at a single "sitting."
• A horse drinks water as he nursed from his dam: by pursing his lips together, leaving only a small crack between them, and using his tongue as a suction pump to draw water up and into the esophagus. Waves of involuntary muscle contraction, known as peristalsis, move the water down to his stomach.
• It takes a horse 12 swallows to drink a quart of water.
• "Binge" drinking is an uncommon vice, but bored horses have been known to drink too much water. Kidney damage and excessive salt intake can also cause overconsumption of water.
• Draft horses, who evolved in cold-weather regions with abundant water supplies, are not physically suited to conserving water. With their blocky bodies, thick skin and insulating fat, they sweat out a larger percentage of body water to cool themselves than do the smaller, lighter horses who originated in hotter, drier climes. Arabians, for example, with their slender heads and necks, shallow bodies and relatively think skin, can cool themselves faster with less sweating.
• A camel can drink 33 gallons of water at a time and go up to eight days without drinking.
• A 1,000-pound horse consumes approximately 10 gallons of water a day. A 150-pound person needs just 2 ½ quarts.
• Bands of wild horses head toward water only after the alpha mare decides it's time for a drink. Dominant bands get first dibs on a watering hole; others wait their turn.
• In the wild, a horse can survive by filling up on water just once every other day.

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Water Needs

On a hot, humid day, a working horse can lose up to four gallons of water an hour—a rate that can’t be replaced by drinking.

• To avoid dangerous water loss in summer, limit your horse's activity when the temperature is over 80 degrees and the humidity is 70 percent or higher.
• Horses ingest water in two ways: through intake of food and liquid, and through metabolism, the breakdown of carbohydrates and other organic molecules in reactions that yield water as a by-product.
• Horses lose water primarily in four ways: excretion in urine and manure, evaporation by breathing, evaporation through the skin, and sweating.
• As horses age, their bodies contain less water, making them more susceptible to dehydration and impaction colic.
• The increased metabolic demands of extremely cold weather may lead a horse to drink even more than he would in warm weather.
• A horse who consumes lush grass, which is 50 to 90 percent water, will need to drink less than a counterpart who eats hay, which is only five to eight percent water.
• Lactation dramatically increases a mare’s need for water. Most foals do not drink much water before weaning; youngsters who seek out water may not be getting sufficient milk from their dams.
• Exhausted or severely dehydrated horses often lose interest in drinking–a situation that calls for immediate veterinary attention to replace body water and electrolytes.
• A dehydrated horse's urine and feces are dark because his body is retaining what little water it has left. His skin may lose its elasticity, and he may appear "tucked up" in his belly and flanks.

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Water in the Environment

Several waterborne contaminants can lead to serious illness, and even death, in horses:

• Botulism usually is caused by the decomposition of dead rodents in the water source. The infected horse suffers paralysis of the swallowing muscles and, ironically, dies of dehydration.
• Anthrax is spread when infected carcasses come in contact with the water source. Signs include acute colic, fever and swelling of the throat, neck and chest.
• Toxic algae are sometimes found in nutrient-rich drainage pools exposed to bright sunlight. Contact with these generally rare species can lead to swelling of the head and legs, erratic movements and loss of appetite.
• Muddy water is harmless to horses, though they probably prefer clean water.
• Groundwater in heavily polluted industrial areas can contain such contaminants as alkali, lead, arsenic, organophosphates and chlorinated hydrocarbons.
• A variety of equine diseases, including rhinopneumonitis, influenza and strangles, can be transmitted via communal watering troughs.
• As a precaution, use your own buckets when visiting an unfamiliar farm or when your horse travels to shows.
• Horses can be picky about unfamiliar water sources, but they usually won't allow themselves to become dehydrated.
• A bored horse may pass the time by blowing bubbles in his bucket or flipping his nose on the surface of the trough, splashing anyone who happens by. In summer, horses with access to natural bodies of water make the most of it, pawing, rolling and wallowing in shallow spots, enjoying the cool water and the respite from insects. More adventurous horses will actually swim through deeper bodies of water. All horses are natural swimmers when riderless; they simply dog-paddle along, with noses held high, "blowing" rhythmically as they swim.

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The article is from EQUUS Magazine, Issue 248 (June 1998), copyright 1998 by PRIMEDIA Enthusiast Publications, Inc. All rights reserved.

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