We put Rabon blocks in for fly control as we run a small herd of Dexter cattle with our Haflingers. Starting with swellings on the belly, small areas the size of a palm appeared on the horse. These are not open and cause no discomfort. A week or so later the size increases. Then open sores with a blood and pus discharge appear. This progress to a single swelling the size of a basketball. In the first horse affected the swelling has over a month gradually decreased and continues to daily. The vets have no answers.