Why and What to Do
About 95% of the egg a hen lays is calcium carbonate by dry weight. Over a year’s time, the calcium she puts into her eggshells could equal 20 times the calcium that’s in her bones. So it only makes sense that a steady supply of calcium will help her stay healthy and produce strong egg shells.
I suggest ground oyster shells, and I recommend putting them in their own container so the hens can take what they need. They like them, they’re readily available in feed stores, and they’re not expensive.
Feed Variances and Calcium
If your hens are fed high quality layer feed and get nothing else, their calcium intake is probably sufficient. But if they’re in the yard, fed table scraps and scratch feeds along with commercial feed, they are good candidates for a calcium supplement.
Note: Only feed oyster shells to hens already laying eggs.