We have 4 feed stores in our small town that started as a farming community and still has a lot of farms. All 4 stores sell only oyster shells. They too all looked at me like I was crazy when I asked for "grit". However, our feed stores are run by men who know what they are talking about and are also farmers and/or raise chickens and deal with farmers every day. What I've learned is that we, here on BYC, treat our chickens like human children and have come up with all sorts of rules, regulations, requirements for raising them that real farmers just laugh at.
Chickens that have access to the ground apparently don't need "grit" because they get it in the form of dirt and sand. They oyster shells not only supply calcium but are an excellent source of grit because well, they're oyster SHELLS. I don't know how long it would take them to break down oyster shell but I know that here in Louisiana we use them for roads and driveways and they never wear out. I'm betting oyster shell stays in the gizzard for a long, long time. It's also nice and sharp and jagged so I think it would do as good a job or better than sand in breaking up food.
Point is relax a little and let your chickens be chickens. They have survived a million years without all the pampering and special provisions.
Chickens that have access to the ground apparently don't need "grit" because they get it in the form of dirt and sand. They oyster shells not only supply calcium but are an excellent source of grit because well, they're oyster SHELLS. I don't know how long it would take them to break down oyster shell but I know that here in Louisiana we use them for roads and driveways and they never wear out. I'm betting oyster shell stays in the gizzard for a long, long time. It's also nice and sharp and jagged so I think it would do as good a job or better than sand in breaking up food.
Point is relax a little and let your chickens be chickens. They have survived a million years without all the pampering and special provisions.