I have been feeding my birds Nutrena All Flock. I keep oyster shell and grit readily available. The All Flock has been working great, but I noticed a couple of the egg shells were a bit thin. My hens have only been laying for less than a month and this is their first season. I was thinking about switching to a layer mix. My concern is for the roosters. I know that roosters don't need the added calcium, but will it be harmful to them if I switched everybody over? *The hens and roos coop together. There are also a couple ducks (male and female) that coop in the same area. They usually eat together as well.