Hello! Please help - one of our Rhode Island Red has a stiff right leg and is now losing feathers on her hock. It's been stiff for about 3 weeks and just started losing feathers last week. She can still sometimes hop on the leg. The other Rhode Island also had a stiff leg but seemed to recover and is now fine. She is about 3.5 months old. We gave polyvisol (no iron) every few days. Do you know what is causing this? Thank you!