I go to the beach and find oyster shells and the reason is similar to your hens, they were not touching the pro manna oyster shells. I started giving them egg shells and the amount they would have to eat wouldnt supplement what they need. Researching oyster shells more, i learned that a lot of them are not even real oyster, instead, something else that still 'does the job', i guess; but my hens wouldnt touch it. They do in fact eat the real oyster shells and when i crack an egg, sometimes its like 2 shells! At first they were anyway, until the novelty ran out. anything new in run gets throughly investigated! Their egg shells are perfect now. If i could afford Peck and Scratch brand i would be using that as my chicken feed full time. As well as oyster shells b/c, well, have you ever crushed ouster shells by hand? I do it with a rock and they dont crush too easily. I actually leave some crushed oyster shells on the ground outside of the coop inbetween my paver rocks. I see them pecking them from time to time.pic is Rosie enjoying some now! Lol