Dehydration in Horses – A Year Round Concern

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.

Salt for Horses in High Temps

High temperatures and high humidity in much of the U.S. have created higher stress conditions for people and for horses.  I have been judging some horse shows recently in outdoor arenas with temperatures well in the 90’s with heat index values 100+ and I can see the impact on the horses as the show progresses.

Horses do require about 1-2 ounces of salt per day to provide help meet their requirement for sodium and chloride under normal temperature conditions.  This requirement can increase to 4-6 ounces of salt per day in hot climates or under exercise where losses in sweat increase greatly.  Inadequate salt in the diet can result in abnormal eating behavior such as licking or chewing objects which have salt on them (fork handles etc.) or licking/eating dirt.  Water intake may also decrease, increasing the risk of impaction colic. In more extreme cases, horses will stop eating and may experience muscle incoordination.

A good option to maintain year around salt intake is to offer loose salt available free choice, either in stalls or in a covered mineral feeder.  Salt intake from loose salt has been observed to be higher than from salt blocks due to the ease of consumption.  It is a challenge for a horse to lick enough salt off a salt block to consume the higher levels required during high heat and humidity. 

If horses are salt starved, it may be a good idea to limit the amount of salt put out for them initially until they have adjusted their intake.  It is absolutely essential that fresh water at an appropriate temperature be available at all times as well.  Horses tend to consume less water if the water temperature is too high, even if they should be drinking more water in the warm, humid conditions.

Commercial feeds normally contain 0.5-1.0% salt, so horses on this type of feed will typically consume less free choice salt than horses not receiving salt in their feed.  They may still benefit from having loose salt available free choice.  A salt block is better than not having any salt available free choice, but may not be as effective in maintaining salt intake when high intakes are required in hot, humid weather.

Providing salt free choice is a good management tool that can help your horse eat and drink well all year long!

Warm Temps & Water Consumption

The transition in temperature and humidity from cool season to warm season may require an adjustment in watering horses. Reduced water consumption may impair performance and may increase the risk of impaction colic. Also, horses that are not conditioned properly may sweat more profusely than a well-conditioned horse, and thus dehydrate faster. This is particularly important early in the season when temperatures may change suddenly and horses may not yet be in peak condition.

The first key element is to make certain that horses have ready access to clean, palatable, cool water at all times or at very frequent intervals. Horses will normally consume about 1 gallon of water per 100 lbs body weight, so an 1100 lb horse will require a minimum of 11 gallons of water per day. This quantity can increase substantially during periods of exercise, high heat/humidity or for lactating mares.

Some tips to keep in mind to keep water consumption up:

  • Horses do not like to consume warm water in warm temperatures. Automatic waterers or large tanks, located in the shade and cleaned regularly, may be good options. If water is supplied in buckets, they need to be cleaned regularly and re-filled regularly.
  • If you are traveling to a show or other competition, it is essential to monitor water consumption, particularly if temperature conditions change.
  • It is routine in many barns to flavor the water with something like wintergreen or peppermint at home so that you can flavor the water in new facilities to match the home water.  Read here for tips on training your horse to drink water away from home.
  • Do NOT use soft drinks or any material containing caffeine as these can trigger positive drug tests.
  • Taking horses to facilities with chlorinated water can sometimes reduce water consumption without proper precautions.

The second key element is to make certain that salt is offered free choice. Things to keep in mind for salt consumption in horses include:

  • Horses require 1-2 ounces of salt per day, and this can increase to 6 ounces per day with exercise in hot weather conditions.
  • Loose salt is consumed more readily than salt blocks in many cases.
  • When evaluating the total diet for salt consumption, commercial feeds normally contain 0.5-1.0% salt. It is not typically any higher than this, due to problems with palatability.
  • If a horse has been salt deficient or is bored, they may over-consume salt while in a stall.
  • Additional electrolytes, commercial or personal recipe, may be used per directions before, during and following completion, but care must be taken to ensure that the horses are drinking adequate water. Administering electrolytes to a horse that is not drinking properly, or allowing a horse to over consume salt without adequate water, can lead to electrolyte imbalances. If electrolytes are added to the water, plain water should be offered also.

Horses need to be offered water throughout the day at a competition, and should be re-hydrated following exertion. They cannot cool out and recover properly without being re-hydrated. Keeping horses properly hydrated and maintaining electrolyte balance is extremely important in order to make a safe transition from cool temperatures to summer time and competition.

Feeding Electrolytes to Horses

As a follow-up to our recent post on providing adequate water for horses, the following information should be helpful in understanding the use of supplemental electrolytes for horses.  There are a wide range of practices and opinions within this topic, so here are some basic guidelines to keep in mind:

  1. Provide loose salt free choice at all times to all horses.  If loose salt is provided, horses will usually consume the right amount to meet their electrolyte requirements without having to use an additional supplement. 
  2. Horses administered any form of electrolytes need to be consuming adequate water.
  3. Electrolytes should never be force fed to a dehydrated horse, and any horses supplemented with electrolytes should be monitored for dehydration (skin pinch test, mucous membrane color and hydration, capillary refill).
  4. Electrolytes can be used to encourage drinking (e.g. during transport or if horse doesn’t like to drink away from home).  Usually thirst/drinking is stimulated within 3-4 hours after dosing. 
  5. In cases where horses are working extremely hard and losing electrolytes through substantial sweating, a supplemental electrolyte in addition to the salt may be beneficial. 
    1. If heavy sweating due to competition is anticipated, administer electrolytes 1-2 days prior to competition, during the competition and 1-2 days after a competition. 
    2. Doses are usually within the 1 – 4 oz range, depending on sweat loss and the heat and humidity levels. 
    3. A general rule of thumb is usually 30 – 90 g per hour of strenuous work, or follow manufacturer’s instructions if using a commercial product. 
  6. An oral dose (paste/syringe) is recommended over top dress or adding to water, as these methods can create palatability issues and can result in feed/water refusal.
  7. Many commercial products have more sugar that electrolytes in them, so buying a commercial product where sugar is not listed as one of the main ingredients is very important.  Potassium, sodium, chloride, and calcium are the most important electrolytes.