It's called Deep Pectoral Myopathy or green muscle disease. It is quite common in broilers, especially males 6 weeks and older. The inner breast muscle's blood supply is reduced and that portion dies and becomes necrotic. Intense exercising of the wings will cause it, the larger the breast the more likely an injury will be sustained. My first experience with it was my last batch of CornishX that had been allowed access to a single stack of straw bales to jump off of and "fly". Out of 29 birds (st run) , 3 birds had DPM. I have never had any issues with my pastured broilers, these birds were unfortunately confined due to weather conditions in the late fall/early winter. I will only have pastured birds from now on, I had no issues with the other 120 pastured birds I raised this summer.
