I don't doubt the need for calcium supplements; but my chickens gladly devour dried eggshells, ground up. Hasn't increased cannibalism, as some fear - they're dried and ground, and the ladies don't think of them as 'that perfect round thing I so brilliantly and uniquely laid this morning' -- but as food or dirt. And no weak shelled eggs at all here. I'm guessing there is something special in addition to the calcium, that one gets from oyster shell? Lay it on me, friends.