Two of my chickens are laying soft-shelled eggs. I've heard that upping calcium can help. I've tried giving them a bowl of oyster shell, mixing oyster shell in their feed, and scattering oyster shell in their run. No dice. They just turn their beaks up at it. I know I could grind up eggshells and add to their feed, but I was hoping for other options. So far I've been tossing in cubes of cheese. Any other ideas?