If you have laying hens, we recommend that you give them ground oyster shells. It is best to do this “free choice” by putting the oyster shells in a separate container, so that the hens can take as much as they need.
The eggshell for each egg that your hen lays is about 95% calcium carbonate by dry weight. In just one year’s time, the amount of calcium that a hen will put into her eggshells can equal 20 times the amount of calcium that is contained in her bones. That’s a lot of calcium. In order to stay healthy and produce strong egg shells, she needs to consume a steady supply of calcium.
A good quality layer feed will contain enough calcium for your hens, if it is the only food they have access to. But if you let your hens forage in the yard or feed them other things, like table scraps or scratch grain in addition to commercial layer feed, they’ll need additional calcium. If your hens are laying thin shelled eggs that break easily when handled, this can indicate that they aren’t receiving enough calcium, but it isn’t a conclusive indicator because excessive phosphorous, disease, or inherited traits can also cause thin egg shells.
We only recommend feeding ground oyster shells to hens that have begun to lay eggs.
For more information about laying hen management, eggs, and egg quality, see Storey’s Guide to Raising Chickens.