Insect-bite hypersensitivity can become a serious issue for horses that react to fly and midge bites.
She says the most common clinical signs are hives and pruritus—a chronic, intense itchiness. “Horses can rub and scratch an area until it’s raw and bleeding,” Knight says.
“Sweet itch is another insect hypersensitivity with horses usually associated with Culicoides,” the little no-see-um midges that tend to come out at dawn and dusk and bite horses around the shoulders, chest, belly, neck, mane, and tail areas.
“Like any allergy there isn’t really a cure for it,” Knight explains. “We try to first to manage exposure and then the symptoms. Knowing which insects are causing the issue and keeping horses in during periods when those insects are most active can be helpful. Have a good manure management program to reduce insect breeding habitat (for flies). Culicoides are not good fliers, so putting horses in a stall with a fan (to produce a strong air current) can be helpful. Pyrethrin-based fly sprays can also be useful to keep insects off horses.”
As far as treating insect-bite hypersensitivity, an owner’s options depend on the horse’s signs. “Topical or systemic steroids may be helpful short-term for relief but are not good long-term solutions because they can have adverse side effects,” says Knight. “Antihistamines can sometimes help with itching and are safer for long-term use.”
Allergy shots are available but only successful in about 20-30% of cases, she says. “A horse owner has to be pretty dedicated, as it can take up to a year to see results.”
Knight explains that researchers are working on an allergy-type vaccine to thwart the chemicals our bodies produce that cause hypersensitivity reactions. Those results are still a ways off, however, and will likely be expensive, she says.
Another option is supplementation with omega-3 fatty acids to help reduce overall inflammation and potentially itchiness. “Feeding supplements high in omega-3 fatty acids, such as ground flaxseed, are a great tool for reducing the severity of the reaction and a good adjunct therapy,” says Knight. Ask your veterinarian for product and administration recommendations.