We sometimes think of dehydration as only a hot weather concern. Horses (and people) can experience dehydration any time they are losing more water from their body than they are taking in to maintain fluid balance. This can be a problem in warm humid conditions, but can also be a problem in warm dry conditions or cold dry conditions. This is a definite concern in cold weather when access to water may be restricted due to frozen water supplies.

Dr. Lon Lewis presented this very handy table on dehydration several years ago in his book Equine Clinical Nutrition: Feeding and Care.

% Dehydration	Possible Symptoms
Less than 5%	No detectable abnormalities are generally present.
6%	Skin becomes slightly inelastic with a pinch test time of longer than 1 second
8%	Capillary refill times goes from normal of 1.5-2 seconds to about 3 seconds Mouth and mucous membranes may be dry Generally the feces will be dry and urine output may decrease
10%	Severe skin elasticity Capillary refill time will be over 3 seconds Extremities will be cold and there may be weakness
12% and greater	Inability to stand Shock Muscle twitching Weak pulse Death can occur at or above this level

For an 1100 pound horse horse, 5% dehydration would mean the horse has lost about 55 pounds of water or about 6.875 gallons (1 gallon = 8 pounds of water).  At 12% dehydration, the 1100 pound horse has lost 132 pounds of fluid or about 16.5 gallons.

You may also see loss of performance and visual signs without doing these tests. I see this in the arena when I am judging, particularly during the hot humid conditions. I confess I have experienced some of the same symptoms when judging a long horse show while wearing a coat and tie! It takes me about 24 hours to rehydrate!

If you are not familiar with the pinch test or capillary refill time, it is a good idea to discuss these tests with your veterinarian as these are important quick tests to check the status of your horse as a part of general first aid along with being able to check pulse and heart rate. In general terms, the skin pinch test is best done over the shoulder or over the back. Capillary refill time can be checked by pressing on the gum to compress the blood vessels, then timing the return to normal color.

Dehydration may be due to many different factors and can contribute to impaction colic as well as heat stress or heat stroke. Dehydration may occur in cool or cold weather as well as hot weather. Horse owners should visit with their veterinarians to make certain they know how to recognize the various symptoms of dehydration.

Having fresh clean water available at all times and providing access to salt free choice (loose salt may be preferred during cold weather) all year long are required to help reduce the risk of dehydration.

Lewis, Lon D. DVM, PhD., Equine Clinical Nutrition: Feeding and Care, Williams & Wilkins, 1995, Table 17-1, page 392.