Every other day or so I am getting 1 egg that is so thin that it is often broken by other hens laying in the same nesting box. They have regular access to layer feed in the coop/run. They also have free access to grit and calcium in the run. I also give them fresh veggies every day (kale, lettuces, fresh corn, tomatoes, squash, discarded shells etc.) They are moved around my yard in a 60 sq/ft tractor every day. They do not have calcium in the tractor but do have access to the layer feed as well as whatever they scrounge up in the yard. Is there another way to supplement calcium to the entire flock so she is forced to get some. I am assuming that she does not pick through the oyster shell that I have out. Or might there be another problem that I am not aware of? Any pointers or ideas?