One final post mortem find, and the end to my keeping of straight meat hybrids...
On both sides of the breastbone of one of the meat hybrid girls I found an area of green discoloration which had also affected the bone itself. This was deep mid-centre of the breast in the tender core muscle that lies against bone. The dead area appeared symmetrical, about 5cm long and 2.5cm wide. In between the bone was dark and eaten right through, connecting both areas of necrosis.
I saw no tumours or true lesions, and no sign of an injury or wound, just necrotic tissue. This perplexed me very much until I found references to something called Deep Pectoral Myopathy. I looked at various sites including www.worldpoultry.net (http://www.worldpoultry.net/diseases/deep-pectoral-myopathy-d95.html) and others. I believe this is what the poor girl had.
Apparently, due to intense selection for breast meat, areas of deep breast muscle may not receive sufficient blood supply, particularly during wing-flapping. Afterward the dead muscle tissue can turn green. Complications such as gangrene are also possible (explaining the eaten-away bone; or to my mind the bone itself may have lost blood supply in the same manner as the muscle, thereby producing bone necrosis).
While it's reassuring to know I didn't cause this issue as such, it's a pretty distasteful find. I can't imagine what pain this bird must have felt when flapping her wings. Meanwhile selection for enhanced meat characteristics goes on, with GM chickens not too far away.
We're told that unless we continue to increase food production, our food systems will be unable to provide for the world's population in the near future. It's hard for me to imagine how the meat bird could possibly be asked to do more for humanity in this regard.