E148
Dehydration in Animals

Introduction: The word dehydration means that there is a lack of fluid or water in the body. Most cases of dehydration are the result of excessive fluid loss (sweating, diarrhea, etc.) or from not drinking sufficient amounts of water. The average horse drinks about 1 gallon of water for every 100 pounds of body weight. This means that the adult horse will drink around 10 gallons of water a day. Any variation to this amount can result in dehydration. Water requirements can vary greatly depending on the type of work the horse is doing, the temperature, humidity, and the diet being fed. For example, horses that are expected to do strenuous work in hot temperatures will require higher amounts of water than a horse that is simply out on pasture. Dehydration can be a serious problem for both young animals and adults. Many times it is a life threatening problem that must be corrected quickly. Realize that dehydration decreases the animal’s ability to distribute medications and nutrients throughout the body.

Horses are more at risk of becoming dehydrated than are humans. This is because a horse's body gets the signal that it is thirsty more slowly than humans. The sweat of horses tends to contain large amounts of salt, making the salt or sodium concentration in the blood stream low. This means that a horse must lose a lot of water before the level of sodium in the blood stream becomes high enough or a significant drop in blood volume occurs for the horse’s thirst center to be activated. As a result, even though a horse is obviously dehydrated, it may not drink when it is lead to water.

Clinical Signs: Sunken eyes, skin remains tented, weakness, pale, dry gums, and a capillary refill time longer than 2 seconds are some of the more common signs of dehydration. Not every animal will experience all of these symptoms. See pages B105 and B115 for additional details on dehydration and skin tent.

Additional Diagnostics: One of the best ways of evaluating the extent of dehydration in an animal and determining if hydration efforts have been successful is by drawing blood and running a complete blood count (CBC). See page D127 for additional details on this procedure.

Assessing Hydration Status: Use the following guidelines to determine the hydration status of an animal:

Treatment: Once the level of dehydration in the horse has been determined, a calculation can be done to identify how much fluid is required.

Hints: 1 gallon = 3.7 liters, 1000 mLs = 1 L, and 1 kg = 2.2 lbs.

This fluid can be given orally (PO) or intravenously (IV). Only sterile fluid should be administered IV. It is essential that any dehydrated animal, particularly newborns with diarrhea, have oral or IV fluid supplementation.

Oral Fluid Administration: Oral fluids alone should only be used in animals that are 1-5% dehydrated. If the animal is more dehydrated than this, oral fluids may not meet the animal’s needs. The most common problems with oral fluid administration are that the method and frequency of administration is not ideal and the quantity administered is often insufficient. To overcome these problems, the following suggestions are a must:

1. Calculate the animal’s fluid requirements using the previous example.
2. If electrolytes are going to be fed, reconstitute them exactly according to the manufacturer’s instructions.
3. The best way for a newborn to obtain oral fluids is by suckling a nipple bottle or drinking from a shallow pan. If the newborn is too weak to suckle, fluids can be administered with a nasogastric tube. This method, however, can be very dangerous to the foal if not done properly.
4. Do not be reluctant to administer milk or milk replacers in addition to electrolytes to newborns. Electrolytes do not contain adequate nutrition for the foal; therefore, milk is necessary. It is true that some milk replacers can increase the amount of diarrhea that is produced, yet this is a necessary trade off for the extra nutrition the animal requires. All electrolytes and milk replacers should be fed at least 30 minutes apart and never mix the two fluids. Milk digestion is slowed when combined with oral electrolytes.
5. Dehydrated adult animals may require oral administration of fluid through a naso-gastric stomach tube.
6. The frequency of fluid administration can be variable and depends on the severity of the fluid loss and management issues. In general, animals that are only slightly dehydrated may require only two oral doses, while animals that are around 5% dehydrated may require oral fluid every 2 hours.

1. Most horses should have access to some sort of salt or mineral block. Because it is difficult to know for sure how much mineral block is being consumed, this may not be enough for some horses.
2. Electrolytes, particularly salt, can be added to the grain portion of the diet. When choosing a store bought product, find one that contains approximately three parts NaCl to one part KCl. It is also helpful to have one that contains calcium and magnesium as well. If these are not available, it is possible to use ordinary table salt combined with "lite salt" in a ratio of three parts table salt to one part "lite salt." Horses that are not being exercised need about 2 ounces of this mixture per day, while horses that are working, need about 3-5 ounces of it per day. When it is being used on the grain ration, it is helpful to use some molasses to help it adhere to the grain particles. For horses that are in competition, it is beneficial to give 2 ounces of this mixture 1-2 hours before competition and then give a small amount every hour or so throughout a long event.
3. Horses that are dehydrated should have the appropriate amounts of electrolytes in their water. It is also important that these horses are allowed small amounts of cool water immediately after the event to help prevent heat stroke (see page E303 for additional information).
4. Horses that are over 5% dehydrated will often need to have their electrolytes administered in intravenous fluids and/or through a nasogastric tube.

Intravenous (IV) Fluid Administration: IV fluid administration requires that a sterile catheter be placed in the animal by a trained professional. Once the catheter is in place, the following should be considered:

1. Only administer sterile fluids (Lactated Ringers, 0.9% saline solution, etc.).
2. Calculate the animal’s fluid needs by utilizing the table and example at the front of this discussion.
3. Many animals with diarrhea are acidotic (meaning that they have a low blood pH). Because of this, bicarbonate may need to be added to the fluid.
4. Supplemental glucose is often necessary. Adding 30 mLs of 50% dextrose solution to 1 liter of IV fluids makes a 1.5% dextrose solution; adding 100 mLs of 50% dextrose to 1 liter makes approximately a 5% dextrose solution.
5. After the initial calculated fluid dose is administered, additional fluids can be given at a rate of 50 mLs for every 2.2 lbs. of body weight, every day. This means that a 1,100 lb. (500 kg) horse that is 5% dehydrated should initially receive a total of 25 liters of fluid. Once the 25 liters are given, a dose of approximately 1 liter of fluid should be given every hour until the animal is fully rehydrated and back to normal.
6. In addition to the 50 mLs/2.2 lbs/day, additional fluid may be required to keep up with continued losses because of diarrhea, etc.

The key to preventing dehydration is to provide a horse with ample opportunities to consume water. This is particularly important when the horse is taken to a new environment or to a competition. To help with this, consider the following suggestions:

1. Studies show that horses do not like to drink water that is icy cold. The best way to overcome this problem in colder climates is to purchase a water heater that keeps the water at a cool to almost warm temperature.
2. Many horses are also very particular about the type of water they will consume. It is not uncommon for a horse to refuse to drink water at a new facility or competition site. To combat this problem it is sometimes necessary to bring water from home or have the horse get used to drinking "flavored" water. The flavored water should be offered at home and then the exact same flavoring should be added to the new water. Water flavored with apple juice seems to be one that works for many horses.
3. Another method used to help prevent the unnecessary loss of fluid is to soak any hay fed to the horse. This helps limit the amount of moisture pulled from the horse’s system when it tries to digest the hay. It is also helpful to offer soaked hay prior to long rides or events. It is also important to offer the horse water in quiet areas without distractions.

* Reference: www.tufts.edu/vet/sports/dehydration.html