Do both!
And I’ve switched to flaked oyster shells, instead of the chunks. My 21-week pullets weren’t impressed by the chunk form, although maybe they just weren’t ready. They love the flakes, which are available on Amazon.
Something I read here that may help you: along with providing 24/7 oyster shells, I also frequently dump egg shells plus some flaked oyster shell on the mulched path just outside the run when I let them out to “yard-range.” The contrast between bright shells and dark path catches their attention, and they clean it up in no time.
I no longer bother with microwaving the shells or excessive cleaning. Just crunch them up a bit and offer.
They’re currently on half layer/half chick feed (both Kalmbach Reserve), as I’m adding pullets next month and am going back to 100% Kalmbach Chickhouse Reserve, with shells on the side.
I ferment their feed, and a couple times I week I smash up one of my 600 mg calcium + vitamin D caplets and add it to the ferment jar.
Their shells are noticeably harder than grocery-store egg shells, even the pasture-raised eggs that are otherwise very good.
