I figured this should be under egg laying since it has to do with that, but feel free to move it if need be. I just recently got my laying hens, 3 are a year old, and 2 I am not sure. Anyway, I was given some oyster shells to grind up, but I'm running out. I'm not sure where to get them now. I've been using ground up egg shells for my girls, is this acceptable for calcium, or do they really need the oyster shells?