An allergy is an exaggerated response from the immune system to a substance in the environment, called an allergen. Horses can become allergic to things they eat, inhale and touch or through insect bite hypersensitivity. Horses that react to insect bites and other skin allergens may develop hives, itching, hair loss, scaling and crusting of the skin and eventually whitening of hairs and thickening of skin in the affected areas. Certain individuals and horse breeds are more allergy-prone than others. The allergic response in these horses may become worse with each encounter, since the horses body is already sensitized. The two primary responses in horses to an allergic reaction either provoke skin sensitivities or respiratory problems. Skin allergies occur predominantly though the contact with allergens. Ingested allergens can manifest themselves as either or both skin sensitivities or respiratory problems. An allergy can decrease performance, be painful, unsightly and can be expensive to diagnose and treat. Secondary issues such as bacterial infections and self-inflicted trauma like tail rubbing can also become an issue. Skin allergies most commonly occur in spring, summer and early autumn, due to allergic reactions to insect bites.
Allergies that manifest themselves as skin related issues cause swellings in the skin. This condition is called urticaria and the bumps are called hives or welts. These raised lumps may be one-third to one inch or more in diameter and often appear in clusters. The bumps are due to dilation of the small blood vessels (capillaries) near the skins surface, which is part of the body’s response to the offending substance. The slow escape of a liquid or gas through porous material or small holes from the damaged capillaries results in the skin swellings. There is usually no itching with hives, unless the problem is caused by allergy to insect bites or stings. The bumps develop suddenly after the horse comes into contact with the offending allergen. If you happen to be with the horse, you can actually see the fairly firm bumps growing as you watch. They usually pop up rather symmetrically on both sides of the body and sometimes on the head and neck. Hives can be caused by a reaction to insect bites or stings, or contact with stinging plants that the horse is sensitive to, or can be caused by eating weeds or plants that produce the allergic reaction. Plant pollens or poisons may also trigger a case of hives. As the liver is the body’s main filter and detoxification unit, the degree or severity of an allergic reaction may be affected by liver impairment. Horses with impaired liver function tend to have more problems with allergic reactions or photosensitization.
Diagnosing an Allergy
The first step in diagnosing an allergy’s source requires two different tests. In the intradermal skin test, the veterinarian will inject minuscule amounts of allergen in the skin and monitor the reactions over a 24-hour period. Blood testing is much more prevalent and involves testing the blood with different allergens to see which ones cause a reaction. Sometimes an allergy test will be conducted and the horses will show sensitivities to everything. Level of sensitivity must then be ascertained in order to move forward in developing a management strategy for the horse. It should be noted that it is not possible to cure allergies but simply manage them.
Most Common Equine Allergens
Common equine allergens include: insects, environmental irritants (dyes, chemicals, urine etc.), mold, grasses and plant pollens. Some specific skin conditions include:
Queensland Itch, sometimes called summer itch or sweet itch, which is caused by an allergic response to the bites of Culicoides midges. Allergy to the insect’s saliva produces an inflammatory, itchy thickening and scabbing of the skin, especially over the rump and/or withers, which may become bare and weepy as the horse scratches these areas. Secondary bacterial infections can occur when the skin is broken in these areas.
Contact dermatitis is an allergic reaction due to direct contact with irritating substances. The irritant may be a chemical such as a dye, preservative used on bridles or saddles, soaps, insect repellents, constant exposure to faeces and urine (as in soiled bedding), contact with certain pasture plants, or even a sensitivity to wound secretions or a topical medication.
Ventral midline dermatitis is swelling and weepy, bare skin along the underline of the belly, caused by sensitivity to certain flies that concentrate there, or to other insect bites that contribute to the problem.
Careful management is the best weapon against skin allergies, attempting to minimize the horses’ reactions by protecting him from exposure to the things that set off his allergies. For a horse that is affected by flies and biting insects, the use of fly repellents, keeping him indoors during the worst times for insect bites, or using a light sheet to protect his body can be helpful. But if a horse continually develops hives or other symptoms in spite of all your precautions, you may have to treat the horse with steroids every second or third day to help clear up the allergy and alleviate the discomfort. Daily dosing with steroids is not recommended, since this may have harmful side effects over time, such as damaging the adrenal glands or compromising the immune system.
Other options for managing allergies in horses can include some nutritional options. Omega 3 fatty acids help synthesize hormones and transport oxygen from red blood cells to tissue, control inflammation and boost immune function. Omega 3 fatty acid deficiencies in humans and animals symptoms include hair loss, skin problems and impaired immune and reproductive function. Nutritional support in the form of antioxidants can also help diminish symptoms and in some cases, strengthen the immune system enough to prevent the allergic response. The trace mineral selenium has an important role in immune response and works with vitamin E to reduce oxidative stress. Vitamin C, vitamin E and folic acid work together to support immune cell activity and tissue health when the immune system is compromised. HYGAIN includes organic selenium, which is highly available as well as natural vitamin E and elevated levels of omega 3 fatty acids in their feeds to ensure optimal immune function in your horse. Check out our range here.