Severe Dehydration

Editor's Note: This excerpt is from Understanding Equine First Aid by Michael Ball, DVM. The book is available from

Dehydration can be a significant problem for the performance horse as well as for horses suffering from other disease processes. If you suspect dehydration, you can check easily your horse's hydration status if you have used one or more of the following methods to establish a base line before the event. Although the tests are somewhat subjective, they can be valuable.

The most common test performed is the so-called "skin-tent test." It is based on the premise that as the skin becomes dehydrated it loses its elasticity. In a dehydrated horse, if the skin is pulled up, or tented, it will snap back to the pre-pinch position more slowly than it normally does. It should be performed in an area that has some degree of consistent tension such as the point of the shoulder. Generally, the skin should snap back to normal in a few seconds. One note: older horses tend to lose the natural elasticity to the skin and it can take longer for their skin to return to place. If you know what is normal for your horse, and perform the test consistently, it can be a useful test of hydration status.

In addition to the skin-tent test, it is desirable to note the degree of moistness of the mucous membranes of the mouth. Dry or tacky mucous membranes are also an indication of dehydration. Pressing on the horse's pink gums and estimating the time it takes for the color at the pressure point to change from white back to pink is also a measure of dehydration. It, too, must be done as a comparison. Also, if the horse's eyes appear to be sunken into their sockets and have lost the luster of the outer surface of the cornea, significant dehydration is probable. Depression and an elevated heart rate are additional, although non-specific, signs of dehydration.

Endurance and event horses can lose a substantial amount of body water (as well as electrolytes) as they sweat. It has been shown that a three-day event horse can lose up to 20 liters (5 gallons) of water during the cross-country phase of an event. It is important to make an effort to prevent dehydration from occurring.

Performance horses can become even mildly to moderately dehydrated before exercising. If the horse does not drink well on the trailer or does not like the new water at the competition site, then its water intake might be considerably reduced--and dehydration started prior to the first drop it sweats.

If you have a horse that is finicky about its water, you might need to try a number of creative (although inconvenient) water-enticing strategies. Every poor drinker is different. Some I've dealt with required bottled supermarket water, while others needed the water from home (brought along in 30 gallon plastic drums). Some horses preferred water with salt added while others accepted the unfamiliar water with oil of peppermint or with a variety of Kool-Aid (unsweetend) flavors added to it. On the subject of salt, it has been shown that the feeding of an electrolyte supplement will not increase the horse's average daily water intake, but many horses will more readily drink water that has had an electrolyte powder added to it in preference to plain water. Care should be taken not to make the water too salty and a salt/mineral block should be available to your horses at all times.

Regardless of the cause, a severely dehydrated horse should receive prompt veterinary attention. It most likely will require intravenous fluids or the forced administration of water via a stomach tube. Many dehydrated horses also have blood-electrolyte abnormalities that require correction.

A final word on dehydration. If you live in a part of the country where keeping water a liquid during certain times of the year is a problem, extra concern is necessary. For example, if a horse (or any other any animal) has been inadvertently deprived of water for several days (or an unknown period of time) due to frozen streams, stock tanks, or water pipes, the animal should not be allowed to drink large quantities of water all at once. It is well documented, especially in pigs, that the rapid and large consumption of water following a period of water deprivation can cause serious brain disease. Water should be offered in small quantities (1 liter at a time for a horse) every few hours until the animal has had its fill and then it can be allowed unlimited access to water.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at or by calling 800/582-5604.

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