Allergies in Horses

The immune system acts to protect the body from potentially dangerous foreign substances. In the case of allergies, the body has associated a harmless stimuli, or allergen, as a danger and initiates a strong immune response. This response and associated symptoms are known as allergies.

Allergies are uncommon in horses. Although the hives that develop from allergies can be extremely itchy and affect horses’ daily activities, they are not life-threatening. Horses require prompt veterinary attention to begin a treatment program and improve their quality of life.

It is not known why a particular allergen is targeted by the body. Severity of the reaction depends on the individual immune system and can vary widely from case to case. Horses may develop hives in a certain location of their body that is affected, such as in the area of an insect bite, or they may cover the entire body, such as in cases where a shampoo was used to bathe the horse. The number of hives and their location is not an indication of severity, as hives are only uncomfortable and not life-threatening.

Horses that are severely itchy may rub themselves on objects or bite at their skin. These horses may develop scrapes, scratches, or wounds that may become infected.

Allergies in horses are similar to other species, where the immune system reacts strongly to an allergen. The most common type of allergies in horses is insect bite hypersensitivity, where the immune system responds to midge bites on the skin. Other potential allergens include:

• Molds
• Dust
• Pollens
• Medications and dewormers
• Chemicals or products in shampoos or insect repellants
• Mites found in forage or in the environment

Food allergies are not well-described in horses. Horses with allergies may experience relief when their feed is changed, however it is unknown whether that is due to a true food allergy or whether exposure to environmental allergens (such as molds, dust, or pollen) changes when the feed is changed.

“Heaves”, or equine asthma, is a form of allergies that affects the respiratory tract. Mold, dust and pollen are the main allergens responsible for this condition.

The most common symptom of allergies is hives, which are raised welts on horses’ skin. Hives are frequently accompanied by itchiness.

The underlying allergen can be difficult to diagnose in horses, particularly since horses are constantly exposed to dust, pollen, and molds which makes completely eliminating these allergens nearly impossible. Diagnostic tests may include:

• Physical examination
• A history of when the allergic reactions occur, including season, changes in environment or feed, or other associated lifestyle changes
• Elimination of specific chemical products, bedding products, grain, hay, supplements, etc. to narrow down potential allergenic triggers
• Intradermal allergy testing

Allergies cannot be cured. Treatment aims at making the horse more comfortable, and reducing future episodes of hives. Strategies include:

• Reducing exposure to the allergen, if known
• Soothing shampoos during hives outbreaks to reduce itchiness
• Antihistamines
• Steroids to reduce the immune response
• Using fly sheets and masks or fly repellents during turnout for insect bite allergies

Some horses respond to allergen immunotherapy. In this treatment, small amounts of the allergen are injected into the skin at increasing doses, to desensitize the immune system.

Allergies are a life-long condition with no true cure. With appropriate management, most horses have reduced symptoms and reduced frequency of allergic episodes, resulting in an improved quality of life. Many well-managed horses can continue their normal activities with minimal effects on performance.

There are no known preventatives for allergies. Allergies are not contagious.

Allergies are uncommon in horses.

• Reducing exposure
• Immunotherapy
• Symptomatic treatment such as soothing shampoos, antihistamines, and steroids