They are getting too many low protein snacks. Cut out the corn and boss, and keep feeding higher protein stuff, maybe switch to a higher protein ration like a game bird, non medicated chick starter, or a meat maker. Keep a separate dish of oyster shells free choice.They get a head of cabbage a week (hanging). Strawberry head scraps and sometimes grapes. They go out in a chicken tractor when its not raining and at night, to get them back into the main coup, they get BOSS. In the winter they were getting a cup of cracked corn at night but I have stopped that since its not too cold out.