I am offering oyster shell free will but they don't seem to be consuming it. They put it in their beak and bite down on it and spit it out like a rock. Should I crush it up into smaller pieces like crumble/mash size like their feed? Or will they eventually eat it as normal size pieces? I have 2 pullets that are giving me soft shelled eggs and one giving nice hard shells. Still waiting for the other 3 to lay first eggs. Suggestions please.