When do I need to stop feeding my chickens chick starter? They're 5 1/2 weeks old now. Also, instead of oyster shells, can I feed them mussel shells? We live by the Kentucky Lake and there are PLENTY of mussel shells. When do I need to feed them oyster,or mussel shells?? - thanks Currently owning, one HYPER lab, 6 chickens, 1 cat, 4 kittens, 2 hermit crabs, 3 snails, a phantom mouse, soon to have 15-30 guineas, and soon to have one beef cow. Good start on a farm, eh?