We have oyster shells to give to our Girls.. they do not seem to like it much, so we thought it needed to be ground smaller, so we did that.. they still do not like it that much. We keep our eggs shells, dry them out and grind them up.. they seem to like those much better.. but why not the oyster shells? All of our 7 Girls eggs are very thick shelled so far, after 2 months laying. Takes two cracks on the cutting board to get them open! We must be doing something right yes? Just surprised that they don;t seem to like the oyster shells is all..