Allergies & Skin HealthBy: Dr. Lydia Gray
An allergy is an exaggerated response from the immune system to a substance in the environment, called an allergen. Although horses can become allergic to things they eat, inhale, or touch, insect bite hypersensitivity (IBH or "sweet itch") is extremely common this time of year. Horses that react to insect bites and other skin allergens may develop hives, itching, hair loss, scaling and crusting, and eventually whitening of hairs and thickening of skin in the affected areas. If the mane and tail are affected and itchy, horses may rub until hairs are broken, developing the classic "rat tail."
Recent studies have shown that supplementing horses with Omega 3 fatty acids helps reduce inflammation. Specifically, a comparison of corn oil to fish oil demonstrated that feeding corn oil (which has much more Omega 6 fatty acids than Omega 3s) resulted in higher amounts of inflammatory markers in the body. Feeding Flax Seed with "sweet itch" caused a significant decrease in the allergic skin response to Culicoides (midges or no-see-ums), the insect that causes the majority of skin allergies in horses.
Other supplements that may help manage a horse's response to seasonal allergens include MSM, adaptogens like those found in APF, as well as probiotics and prebiotics, which help support the GI system, where most of the body's immune system is located. SmartBug-Off® combines Omega 3 fatty acids, MSM and antioxidants for skin health with Garlic, Brewer's Yeast and Apple Cider Vinegar â€“ ingredients that help deter biting insects.
Allergies are diagnosed by the owner's description of the problem, the clinical signs in the horse, and tests such as skin scrapings, biopsies and cultures that rule out other conditions like parasites, fungus or bacteria. Once all signs point to allergy as the diagnosis, specific allergy testing can be performed to confirm the diagnosis and assist with treatment. Most experts agree that intradermal (skin) allergy testing is better than serologic (blood) allergy testing at identifying allergens for a particular horse.
The first line of defense against allergies is steroids such as dexamethasone and prednisolone, as well as antihistamines such as hydroxyzine and pyrilamine. Like people and other animals, horses can be hyposensitized with a series of "allergy shots" to substances in the environment, identified by allergy testing.
The main way to avoid allergic reactions in horses is to avoid exposing them to allergens. Because horses can be allergic to more than one thing, it may not be necessary to remove every substance that causes a reaction, just enough of them so the horse doesn't have uncomfortable or unsightly clinical signs.
- Protecting your horse from insects by using fly spray, fly masks, fly sheets and fly boots; by putting fans in stalls; and by keeping your horse inside during the times of day when bugs are worst
- Reducing insect numbers by using feed-through insect control supplements, Fly Predators, and good management practices such as manure removal and eliminating standing water
- Noting anything that comes into contact with your horse's skin such as bedding, horse care products (e.g. shampoos) and tack care products (e.g. leather cleaner)
- Minimizing dust in the barn by changing the type of bedding you use, improving ventilation, wetting aisles before sweeping, and other practices
- Using dietary trials to determine if something your horse is eating (grass, hay, grain, treats, supplements) is causing a reaction
- Moving your horse to another barn or in extreme cases, another state, to avoid allergens specific to that geographic location
- What can I do to make my horse more comfortable when he has hives or itching?
- Are allergies something that can be passed down to offspring?
- Will my horse have to receive "allergy shots" for the rest of his life?
- Why is my horse also on antibiotics for allergic skin disease?
Further Reading for You
From our Ask the Vet Blog:
From The Horse Journal:
- Get on Top of Horse Allergies, June 2007
- Knock out Allergies, April 2005
- Win the Allergy War, October 2001
Further Reading for Your Veterinarian
Cunningham FM, Dunkel B. Equine recurrent airway obstruction and insect bite hypersensitivity: understanding the diseases and uncovering possible new therapeutic approaches. Vet J. 2008 Sep;177(3):307-308..
Morgan EE, Miller WH Jr, Wagner B. A comparison of intradermal testing and detection of allergen-specific immunoglublin E in serum by enzyme-linked immunosorbent assay in horses affected with skin hypersensitivity. Vet Immunol Immunopathol. 2007 Dec 15;120(3-4):160-167.
O'Neill W, McKee S, Clarke AF. Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity.