I've always thought of spring as allergy season but I've been hit hard with some type of allergy reaction over the past couple weeks; sinus headaches, runny nose, etc. Just miserable. I've also gotten an increase in the phone calls and e-mails from horse owners concerned about allergies from which their horses seem to be suffering. So, I'm posting an article I've written on horses and allergies to help horse owners sort through how to deal with the various manifestations of alleric reactions in horses.
If you’ve ever experienced a horse with allergies, you know it can be a frustrating situation for both horse and horse owner. Frustrating for the horse with runny eyes and welts or itching and rubbing constantly while nothing seems to provide relief. Frustrating for the owner because you are trying desperately to find out what caused the problem and how to fix it.
Allergic reactions are essentially an immune system in over-drive. An allergy is an abnormal reaction by the immune system against a normally harmless substance. The first exposure to the allergen causes white blood cells to produce antibodies that prepare the immune system for the next encounter with that same allergen. No outward signs occur at this point. The antibodies attaches to mast cells that are found in the respiratory system, gastrointestinal tract and the skin. During the next exposure, the allergens will combine with the antibodies and release chemicals, such as histamine or leukotrienes, which produce the allergy symptoms. The resulting allergy symptoms depend on where in the body the chemicals are released, and are generally some manifestation of inflammation.
The most common symptoms in horses associated with allergies are skin irritations such as hives, welts, and itching (urticaria) or respiratory problems such as recurrent airway obstruction (RAO) which is very similar to asthma in people. Weepy eyes, nasal discharge or digestive upsets can also be symptoms of allergic reactions. These symptoms can be caused by contact dermatitis from exposure to organophosphate pesticides, heavy metals, dyes, bedding, topical medications, soaps, shampoos, blankets, wool and neat’s-foot oil. Other causes include atopy, an inherited predisposition to environmental allergen sensitivity, and “sweet itch” which is hypersensitivity to insects such as culicoides. Food allergies are commonly suspected but rarely prove to be the true cause of allergies in horses. Even in people, true food allergies affect only about 6 – 8% of children and 2% of adults.
An allergic reaction to protein normally causes what are historically referred to as "protein bumps" on horses. Instead of large soft welts, protein bumps are usually hard little bumps like a large BB under the skin. They may be a reaction to a certain protein, not necessarily of dietary origin, but may be from a protein injected in the skin when insects bite. Other skin reactions cause scabby eruptions on the skin that usually itch, causing the horse to rub enough to lose hair and even cause sores. These may be from an allergic reaction or a bacterial infection. Scabs can be cultured to determine if there is a bacterial infection and a regimen of antibiotics may resolve the issue.
Allergy symptoms such as hives, runny eyes, nasal discharge and coughing may be more indicative of an inhaled allergen. Removing long-stemmed hay and using a complete feed that is formulated to replace hay often helps alleviate these problems. Other management options including immersing hay thoroughly in water before feeding, feeding in a trough at ground level, wetting stall bedding or changing the type of bedding, and providing as much pasture time as possible will help minimize exposure to respirable dust and molds. In almost all cases symptoms due to inhaled allergens will improve if the horse is kept outdoors. Even short amounts of time in barns or trailers will exacerbate symptoms.
Determining the cause of allergy symptoms can be quite an exercise in trial and error. In humans, the gold standard for diagnosing food allergies is a double-blind, placebo-controlled food challenge. A reaction is expected within a few minutes to 2 hours after ingestion but this is a very involved and expensive procedure. Other allergy tests include a skin prick test or a patch test where extracts of various foods, or other potential allergens, are injected into the skin. Reactions (called weals) at the injection or prick site are measured to determine sensitivity level. Many horse owners opt for a blood analysis that will measure antibody levels to various potential allergens including insects, molds, pollens, plants and foods. These blood tests are a tool that may help identify potential triggers for allergy symptoms but often have a high rate of false positives, especially for identifying food allergens. Rarely do the allergy symptoms resolve when the diet is adjusted according to the results of these blood tests.
The only reliable diagnosis of a food allergy is an elimination diet. One difficulty with this is finding a diet that contains none of the identified potential allergens but still meets the horse's nutrient requirements. Sometimes that is absolutely impossible because of the long list of potential allergens. A horse that has previously been on a good plane of nutrition can be fed a hay-only diet for one to four weeks to see if the symptoms resolve. If they don’t improve then the symptoms weren’t caused by a food allergy and you have to look for other causes. If symptoms do resolve, then very gradually introduce one new food at a time in an effort to build a balanced diet that will not trigger an allergic response.
There is anecdotal evidence that feeding omega 3 fatty acids from a fat supplement such as Purina Nature’s Essentials AmplifyTM supplement may help resolve symptoms of skin irritation and inflammation. Feeding 1 – 1.5 lbs per day of AmplifyTM to horses suffering from sweet itch has been reported to result in cessation of itching and hair re-growth within 45 days.
If your horse is exhibiting allergy symptoms, get your veterinarian involved. They can help relieve discomfort associated with the symptoms and help you determine what changes in environment or management may best help manage through the symptoms. Then, just wait for a new season when most symptoms will spontaneously disappear....until next season.