Hives in Horses: Symptoms and Treatment

Q: I noticed the other day that my Appaloosa gelding had hair standing up and welts on his skin. A friend suggested that he might have hives. What can you tell me about hives on horses? What kind of treatment should he have?




Note the localized hives on the side and hip of this event horse. This was thought to have been caused by a chemical irritation (fly spray).

The welts or wheals that you have noticed on your horse are indeed indicative of the skin condition known as hives. The condition's proper name is urticaria, and it is characterized by these bumps, which are really localized edemas or swellings in multiple sites. The swellings result when the capillaries beneath the skin leak a clear fluid from the blood into the tissue spaces below the skin's surface.

This condition in horses is similar to hives in humans. Most cases are allergic in origin, and there are many different causes of the allergic reaction. Hives can be caused by reactions to drugs, especially to antibiotics and nonsteroidal anti-inflammatory drugs. Other causes include allergies to food, reactions to topical drugs or ointments placed on the skin, and seasonal reactions to pollen and molds in the environment. Occasionally hives are secondary to digestive disturbances.

The welts that you have noticed occur most often on the neck and shoulder, but occasionally they can be found all over the body, including the legs. Most cases of hives are mild, but it is possible to develop a more acute case and the swellings can converge, forming a larger area. If the situation should progress to this point, it can present a difficulty, especially if the swelling impairs the horse's ability to breathe.

Another symptom of hives is itching. You may or may not have noticed your horse rubbing various areas of his body on the fence or the barn or any other surface that will provide him some relief. The intensity of the itching will vary, from mild annoyance to severe scratching at any risk. If the itching should reach the latter stage, the attempts to relieve the itching could result in injury.

Although urticaria (hives) is common in horses, there is no diagnostic test for it. However, the diagnosis is the easy part. Being able to say that the skin condition is indeed hives is easy. What is not easy is determining the source of the problem. In order to keep hives from recurring, it will be beneficial for you to know the cause. The best way is to eliminate the possible causes from your horse's environment. We know generally the kinds of things that cause hives; therefore, look at your horse's environment and his medical history (Has he been given any medication or treated with any ointments lately? Have you changed your brand of fly spray? Have you changed the type of feed or hay that your horse has been eating? Have you changed the type of bedding?). After that you can begin to narrow down the possible source. Also, there are external factors such as heat, cold, exercise, and stress that might intensify the allergic reaction.

The best treatment for hives is, of course, to eliminate the source of the problem. Since that approach rarely is accomplished quickly, it often is necessary to treat the animal to relieve the signs. This is especially true if the reaction is progressing, and if further swelling is threatening to interfere with normal functions. In these acute situations, the best treatment is most likely one of the fast-acting corticosteroids, such as predisolone sodium succinate. This, and similar cortisone derivatives, are given intravenously and should only be administered under your veterinarian's direction.

Occasionally the reaction to the disorder is life-threatening (for example, when there is a swelling in the throat resulting in impaired breathing), and epinephrine (adrenaline) may be needed to reverse the swelling quickly. Reactions of this nature might follow the administration of medications in an improper manner, such as procaine penicillin administered intravenously by accident.

Fortunately, most cases of hives are not critical. Slower-acting corticosteroids might be effective as well as some of the non-steroidal anti-inflammatory drugs. There are mixed reviews on antihistamines for this condition, with the majority of veterinarians choosing other treatments.

Your horse might not exhibit any signs of extreme discomfort or pain from hives, but rest assured he really does not feel good, so it might not be advisable to pursue any plans to show your horse. If you intend on showing your horse in a halter class or any other kind of class that is based on general appearance, you might want to reconsider. He is not at his cosmetic best at this time. If you want to him to perform, he can probably oblige; however, if you want him to perform to his ultimate best, he probably will not be able to comply. When we ask our horses to perform, we want them at the peak of their ability, both physically and mentally. When a horse is suffering from even a mild case of hives, it remains doubtful if he feels up to giving you and his best performance.

The problem of hives can recur with regularity. It is up to you to determine the source of your horse's problem. There is allergy testing that can be done on horses just as it is done on humans if the condition persists.

About the Author

A.C. Asbury, DVM

A. C. (Woody) Asbury received his DVM from Michigan State University in 1956, then spent 21 years in California in breeding farm practice and at UC Davis. He joined the faculty at the University of Florida in 1977 and was involved in teaching, research, and administration until 1996. An Emeritus Professor at Florida, he lives in Kentucky, where he and his wife are developing a small farm.

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