Some Horses are Hypersensitive to Insect Bites

It’s show season, and you want your horses looking their best. Then you notice that some have bumps, hair loss, flaky skin…not what makes horses look their best in the arena. Those places also are irritating to the horse–especially if the irritations are in his girth area–making him unhappy to be groomed or saddled. Unfortunately there are many things that can make a horse’s skin react in these ways, but sometimes it is as simple as an allergic reaction to bug bites. In this article from Kentucky Equine Research, we find out more about horses that have allergic reactions to insect bites.

Insect bite hypersensitivity (bug bite allergy) is a common problem during the summer. Susceptible horses are actually allergic to insect saliva. Horses can have allergic reactions to any biting insect, but the most common are Culicoides spp. (no-see-ums, gnats, midges, sand flies and punkies), black flies, stable flies, horse flies and mosquitoes.

Horses with insect bite allergies may have any combination of hives, itchiness, hair loss, and dermatitis. The diagnosis of insect bite hypersensitivity is usually made by clinical signs and the time of year that they occur. Definitive diagnosis can only be made with intradermal allergy testing.

Treatment must first involve avoidance and repelling insects. Most fly sprays contain pyrethrin, insecticides that break down when exposed to the ultraviolet light in sunlight. For this reason, it is important to read the label of pyrethrin fly sprays to be sure that they also contain a sunscreen to lengthen activity.

Culicoides spp. prefer to feed at dusk and dawn, so horses can be turned out to avoid the times of the day when these insects are most likely to be active. Box fans on stalls help to keep Culicoides spp. off horses because the insects are very small and they avoid strong air currents. Routine barn maintenance, such as removal of manure and standing water, disrupts insect breeding and reduces their numbers.

Initial treatment of insect bite hypersensitivity is aimed at breaking the cycle of itching and/or hives. Decreasing doses of corticosteroids can be given to reduce inflammation (discuss this and all medical treatments with your veterinarian, especially if you are showing in recognized shows that drug test). In most cases, antihistamines alone are ineffective. Hyposensitization injections (allergy shots) can be used in horses that have insect bite allergies confirmed with skin testing. Unfortunately, it is difficult to produce pure insect saliva antigens and most are made from the entire insect.

Omega-3 fatty acids can be very beneficial as a long-term therapy for horses with insect bite hypersensitivity or other allergies. Omega-3 fatty acids reduce skin inflammation and also promote a healthy hair coat without the possible side effects of corticosteroids. Most horses with insect bite hypersensitivity can be managed with insect repellants, strategic turnout, dietary supplementation of omega-3 fatty acids, and symptomatic anti-inflammatory therapy during the height of insect season.



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