I was told by a woman that works at the feed store and raises chickens that if you feed dumour feed additional grit and oyster shell isn't necessary. Is this true? Should I still offer it? They are on the finisher right now. If oyster shell is for additional calcium and too much calcium is harmful for chickens is it ok to offer a bin of oyster shell and will it hurt the rooster if he gets too much calcium? I was thinking of 2 separate bins in addition to their feed bin - one for the grit and another for the oyster shell. Also...how much space is needed for each chicken at the feed bin. I am thinking mine is too small for 4 chickens. I thought I read enough room for one chicken to feed at a time but mine seem to like to eat at the same time.