I've had problems with multiple chickens. They start off limping, then go lame. They sometimes will move one leg bot won't stand on it, others have lost movement in one leg toes are not curled. They open and close their mouths, not necessarily panting but repetitive. Decrease weight, generally green stool. Have given poultry cell at the first sign of limping but still gets worse. I've had one that has been in the house like this for a month. I've noticed a couple of them have white spots in their mouths (the two that are panting), one of these two has had crop issues.