I've been feeding the shells back to mine for a long time. I don't have any egg eaters either. I don't even bother cooking them though, I just crush them up. The ladies seem to love them.
For $4, you can buy a 25# bag of calcium carbonate, or calcium lime at many farm/garden stores. Just be sure the magnesium portion is not the 30% type typical of dolomite lime, IIRC. Calcium Lime is only 12% magnesium or less. Or, toss it into the litter in the coop and they'll pick at zestfully.
A handful mixed into the feed, dampen to hide it or blend it, if necessary.
Agree on feeding back the egg shells. Those are free. I've never purchased oyster shell.
I have not given my chickens or chicks any shells,they are laying fine,eggs are good and healthy,andsome of the best tasting eggs around,i give my chickens love bread lots of veggies,tomatoes,squash,cucumbers,eggplants,taters,ect.ect.ect.but noe shells
Quote:
Because in my religion OYSTERS are unclean.... we eat kosher, if the chickens eat the oyster shells, then they become unclean and cannot be eaten!