One of my silkie hens has been laying soft shell eggs for about a month now. It started when she was broody, and i wasn't concerned then, thinking she just wasn't getting enough nutrients. But she hasn't been broody for weeks and it is still continuing. i thought i read somewhere here that it may be due to a vitamin deficiency, but can't find that post now. i provide plenty of crushed oyster shell, they get yogurt or scrambled eggs and plenty of greens every day. i bake and crush their own shells and offer those back free choice. The hen whom i suspect is the culprit seems healthy and normal. Any ideas?