I have 8 Barred Rocks and suddenly one of them is having problems walking. She can stand and walk short distances but it is clear that something is wrong. She often "sits" on her fore legs and she walks slowly with a strange sort of limp. All of the other chickens are fine and she can't keep up with them. She stays behind at the coup while the others range. I have heard of some sort of vitamin deficiencies causing problems with legs but our chickens eat good chicken food, garden scraps and are free ranged. Any suggestions would be greatly appreciated.