Ok so I know this has probably been asked before but I couldn't find anything on it when searching. I live in southern Arizona. All we have here is rocks, gravel and dirt. My chickens have access to all this. Do I still need to provide grit? They are about 6 months old, fat and healthy, and all they have had so far is Arizona dirt so I don't think its too imperative they have it, but I want opinions so lets have Em!