I own three ducks and four chickens and recently discovered one of my ducks is a male. Originally my plan was to integrate everyone to share layer feed, but now I don't want to feed my male duck excess calcium. So I bought normal flock grower food and I bought oyster shell to supplement the chickens for now since the ducks haven't started laying yet. However, the chickens don't seem to be eating oyster shell, like it's maybe too hard or something. But their eggs don't seem to have thin shells, so I was wondering if they are getting the calcium needed from walking around the yard during the day, or if maybe the oyster shell needs to be crushed more. Any feedback or experience would be helpful.