I have 1 EE that is laying a very very tin shell. Sometimes it is broken and crushed by te time I get it and when I do get to it before its broken it usually breaks apaprt as I pick it up. All the chickens get free choice oyster shell and no other chicken is having similair issues. All other chickens lay nice thick shell. Also I am not exactly sure which of the 4 EE is the one laying the thin shell. What should I do???? What could be causing this?