Allergies in Horses

Anyone with allergies knows how frustrating allergies can be, and how frustrating it may have been to find out exactly what you are allergic to. It is no less frustrating for horses and their owners; frustrating for the owners who are desperately seeking cause and remedy; frustrating for the horses who can find little relief from runny eyes, welts or itching.

Any dictionary will explain to you that an allergy is a strong abnormal reaction by the immune system to a normally harmless substance or substances located in the environment. These “allergens” can be introduced into the body by inhalation, ingestion, or skin contact, the reaction often manifested by itchy eyes, runny nose, wheezing, skin rash, or diarrhea. When first exposed to the allergen, the leukocytes or white blood cells produce antibodies to prepare the body’s immune system for its next encounter with the particular allergen in question. At this point, you don’t see any outward signs. The resulting antibodies attach themselves to what is known as a “mast” cell which is simply a large granular cell commonly present in connective tissue, capable of producing heparin, histamine, and serotonin. These mast cells are found in the respiratory system, the gastrointestinal tract, as well as the skin.

 Once the next exposure occurs, allergens will react with the antibodies releasing the chemicals that produce the allergic reaction. These symptoms can show up in other ways depending on the part of body affected, but are almost always in the form of an inflammation of some kind. In horses, the most typical manifestation is either a skin irritation like hives, welts, urticaria or a respiratory problem comparable to asthma in humans. Other allergic reaction symptoms include tearing eyes, runny nose, or digestive upset. Contact dermatitis is a result of exposure to foreign substances such as pesticides, heavy metals, dyes, topical medications, soaps, shampoos, blankets, wool, and poison ivy or poison oak. Atopy, or the tendency to be “hyperallergic” and SSRD (Seasonal Recurrent Dermatitis), which is a medical condition caused by hypersensitivity to insect bites, particularly midges, are also triggers for allergy-related symptoms.

 What are commonly called “protein bumps”, which resemble large BBs underneath the skin, are caused by an allergic reaction to a certain protein, usually a protein introduced by an insect bite. Scabby itchy outbreaks on the skin are the signs of another allergic reaction which causes the horse to rub the spot often enough to remove hair thus creating a sore or sores. A culture of the sores can assess whether it is an allergic reaction or a bacterial infection, in which case a treatment with antibiotics can alleviate the condition.

 Inhaled allergens are more likely to cause hives, teary eyes, runny nose, and coughing. These symptoms are often alleviated by replacing hay with a compete feed formulated to replace hay, thus decreasing the amount of dust and pollen from hay or submerging the hay in water before feeding. Wetting down stall bedding or completely changing the kind of bedding, and arranging for all the pasture time as possible, are the additional management choices available.

Attempting to determine the exact cause of an allergic reaction can be simultaneously frustrating and expensive, and usually ends up being an application of the “Trial and Error” test. In the matter of a food allergy, the sole reliable way of pinpointing which food is causing the allergy is an elimination diet. The difficult therein lies in the fact that finding a diet containing none of the suspect allergens and yet meeting a horse’s nutrition criteria is virtually impossible. One option is to place the horse on a hay only diet for a couple of weeks to see if the symptoms disappear. In the event the symptoms do not disappear, then it would be safe to conclude that the allergy is not food-related. Should the symptoms disappear, reintroduce each separate food one at a time until one triggers an allergic reaction.

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