My girls are all living together now, in the same chicken tractor. They are 14 weeks old and 20 weeks old. Right now they are all eating pullet feed. The older girls are about to lay. Should I be switching them to a high calcium feed? Is it ok for the younger ones to eat that as well? They live together so I can't feed them different food. Also, should I be giving them a calcium supplement? A calcium block or oyster shells? Or will the new food cover that need?