My hens are now 9 months old. I've 14 hens and since they started laying in December, they consistently produce an average of 1 doz eggs per day. When they first started laying, I (a "store egg" kinda guy) was surprised at how hard the shells were. Strong and thick...........so much so it took the back edge of a butter knife to efficiently crack them for the skillet. Now, it seems, the shells are still strong........................but just not as strong as I remember them being only 3 or 4 months ago. I free feed oyster shell...........and clean and return their own shells in bits and pieces to the yard. They are fed Purina brand Layena, so with the extra oyster shell and eggs shells I'd think they are getting enough of what they need. Any thoughts as to why I may be getting more delicate shells?