Our chickens are about nine months old and it is a shared flock of 15. The other owner feels that they need scratch feed. We are feeding Purina Laying Crumbles and as I think I read on the bag, nothing more is needed. What is the scratch feed for other than a treat? Is it needed? We are having a few shells beginning to seem fragile as they are hard to crack open (shell softer and inner membrane is strong) and some have dents on the ends when we gather them. I see some growers feed back the shells or give oyster shells separately for that problem. Any comments on scratch and shells?