Here in Florida, spring marks the beginning of allergies for both people and horses. We see the emergence of mosquitoes, gnats, and flies. Not to mention, everything starts pollinating. Its an allergic nightmare! The most common allergy we see in horses is cullacoides hypersensitivity. Cullacoides are a species of gnats. The females feed on blood (i.e. they bite) and can be a real nuisanse to even the normal horse. The allergic horse, however, has a heightened response to these little bugs and they become unbelievably itchy. Cullacoides swarm at dusk and dawn in the vicinity of marsh, water, or rotting vegetation. They lay their eggs in manure, damp soil, or slow moving water.
When presented with an itchy horse, the first thing we want to ask: is this a year long problem or a seasonal problem? And, what is the distribution of the hair loss and itching? For cullacoides hypersensitivity in North Florida, it is often a seasonal problem. The season is long (usually about 8 months... spring, summer, fall) and the distribution of hair loss is along the face, chest, belly, between the back legs, tail head, and mane. These horses may itch themselves until they bleed and have open sores. They may also develop secondary bacterial infections if left untreated.
Treatment varies depending on the severity of the allergy. Your veterinarian can prescribe one or a combination of the following drugs: steroids, anti-histamines, topical salves/sprays, or allergy shots. Its important that you manage their environment as well. Keep allergic horses under a fan at dusk and dawn. Also use a fly spray with at least 2% permethrin and apply twice daily.
If you see that your horse has areas of hair loss, inflammation or dermatitis, contact your veterinarian for an exam. It is important to rule out contact dermatitis, bacterial dermatitis, autoimmune disease, and parasitism before starting treatment.