I give my girls oyster shell, free choice, but have never seen any of them eat it. They're mostly not laying now, but I'm curious about it. They will eat egg shell that I feed back to them, but are completely uninterested in the oyster shell. How do I tell if they are getting enough calcium in their diet? The coop is in an area that the utility company regularly digs up, which around here means plenty of ground up limestone. Could they be getting enough calcium from the dirt here? I haven't had any issue with thin eggs. Also, how should it take for 4 hens to eat 20 lbs of layer pellets? They are going through more with the cold weather but they still don't seem to eat much. They are on the lawn all day, free ranging, but it is just a smallish backyard.