1: Systemic treatment with a dewormer containing Ivermectin. Treat twice, approximately 3-4 weeks appart.
2: Topical treatment with Dr. Porter's summer sore cream!!
3: If the summer sore is excessively large or in a location that is difficult to treat with topical medication, I recommend systemic therapy with corticosteroids. I prefer to medicate with a tapering dose of oral prednisolone over 30 days.
It is critical that the barn management incorporate a fly control program of their choosing. In addition, horses which suffer from recurring summer sores need to be treated the moment there is any redness or mild irritation present in the old summer sore sites!! If treated early, the lesion will typically respond favorably to topical medication without the need for systemic corticosteroids!