I have six hens I purchased when they were just starting to lay. I'm guessing they are about a year old now. Five of my hens are laying normal eggs, one consistently lays eggs with no shell. This has been going on for a few weeks now. They are all fed the same layer feed, and oyster shell is always available to them. Matter of fact, I now have it in a few spots in the yard to make sure the others aren't bullying her and keeping her from it. Is this a sign of poor health requiring a vet, or just a sign of a picky eater?