Pigeon Fever is the layman term for this disease. It gets it's name because the deep abscesses that form on the horses chest give the horse a pigeon breast appearance. The organism that causes the disease is a bacteria that is passed to the horse via a fly bite. The exact mechanism of the disease is not known however it is suspected that the disease cutaneous habronemiasis which is caused by a fly larvae that migrates in the tissues of the horse may be associated with Pigeon fever. I myself do not put horses with Pigeon fever on antibiotics unless the horse is acting sick. Usually the normal defense mechanism of the horse pushes the abscess outward for external rupture. Once the abscess is lanced then I will place the horse on antibiotics just as I would for any type of external wound. Do not take Pigeon fever lightly. Although the majority of horses make a full recovery some of these abscesses can internalize and kill a horse. It is always a good idea to have your vet take a look at the horse to make sure which course of action is appropriate.