What is Hives (Urticaria)?
Urticaria, known more commonly as hives, is a common skin reaction in horses. Although hives are not generally life-threatening, they can develop into more serious problems. These small raised wheals are extremely itchy, and if your horse scratches to excess, they may become even more inflamed or even rupture, which can lead to dangerous skin infections. Swelling that occurs in the throat and nasal passages is rare, but when it happens it can make breathing difficult, if not impossible.
Hives in horses are small rounded lumps and bumps on the skin; they are usually not painful or life threatening unless they cause the throat to swell.
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Symptoms of Hives (Urticaria) in Horses
Urticaria, better known as hives, is a unexceptional skin condition for the horse. The primary symptom is rounded bumps on the skin that can occur anywhere on the body, and quite often in large numbers. Some additional symptoms that can accompany urticaria include:
- Loss of appetite
- Poor performance
- Restlessness and excitability
- Swollen lips or muzzle
Hives are often caused by an allergic reaction. Other skin disorders caused by an allergic reaction can include:
- Angioedema - Bumps similar in size to hives but found subcutaneously, in the fatty layer beneath the skin; angioedema may occur with or without hives, and the itching and burning sensations can be intense
- Atopy - Atopy is an allergic reaction characterized by inflamed and itchy skin; horses with atopy may also develop papules, tiny raised bumps, which are usually under a centimeter in diameter
Causes of Hives (Urticaria) in Horses
Allergic reactions are the most common cause of hives, and the allergic reaction may be a response to allergens such as biting or stinging insects, ingested plants or insects, or to a substance that came into contact with the horse's skin. Other conditions that can cause hives to form include:
Diagnosis of Hives (Urticaria) in Horses
Hives have a distinctive raised appearance and are frequently diagnosed visually. In many cases, the hives disappear on their own before the animal is even able to be evaluated by a veterinarian. When they are serious enough for examination, the primary diagnostic focus is not on the hives themselves, but rather on what caused the hives to develop in the first place. Hives are caused by allergic reaction more often than by anything else, so determining the correct allergen is the primary focus.
Skin scrapings will often be taken from any areas that are affected by the hives or by other types of rash, for use in the microscopic examination of the skin cells to look for issues like signs of disease, mites, or yeast infections. This type of evaluation is called a cutaneous cytology. In some cases, small amounts of the suspected allergen or allergens are injected under the skin to determine which substance the animal is allergic to.
Treatment of Hives (Urticaria) in Horses
Quite often urticaria disappears spontaneously, and may never be explained. but in cases where it persists, your veterinarian may prescribe a steroid injection or steroids added into the feed. As hives are a common symptom with drug allergies, all medications should be stopped if your horse is experiencing hives that don’t dissipate in just a few hours. Antihistamines formulated for horses such as hydroxyzine pamoate and cetirizine can be quite effective, as can doxepin, a tricyclic antidepressant with the properties of an antihistamine. Horses generally respond quite well to antihistamines, and very few equines develop either excitability or drowsiness from taking them.
Another option for relieving allergy symptoms in horses is called hyposensitization. Hyposensitization is a technique in which the animal is injected with a formula specifically designed for the horse's specific allergies. Although this treatment may show significant improvement in as few as two months, a minimum of a full twelve months is generally required for maximum success. If the hives appear to be related to biting insects, insect repellent formulated for horses, or a fly sheet and mask should be used.
Recovery of Hives (Urticaria) in Horses
The prognosis of urticaria is dependent on the severity of the case and whether or not it reoccurs. Many cases of urticaria do not reoccur, and quite often the allergen or other cause may never be definitively diagnosed. When the hives are persistent the prognosis for clearing up the lumps and bumps may be more guarded, although equine antihistamines are often helpful in relieving symptoms. Allergies in the horse can be difficult to pin down and some veterinarians and horse owners find it easier to simply change the horse’s environment as much as possible. This can include changing the horses usual feed, pasture, and stall.