I recently started giving my hens oyster shell as a choice. They seem to love it, though now I'm noticing more egg abnormalities than ever before. The shells are wrinkly in appearance and hard to crack. I have had my chickens for nearly 5 years and they never appeared to need oyster shell, however a neighbor suggested it and now my relatives believe that my hens absolutely need it. Before I added the oyster shell, I got one abnormal egg (maybe) every month, from my 19 hens. Now, I get a couple every week. Should I discontinue the use?