Can someone clear this up for me? I understand that oyster shells help with calcium.
And grit (what is grit exactly) help with digestion. Since oysters shells is coarse would it not act as double duty?
Oyster shells aren't a hard as stone grit so it breaks down too easily. Plus a chicken may need grit but not extra calcium and vice versa. Always provide both. I actually don't provide grit as my chickens have access to gravel and ground. In the winter I make sure they have gravel available in the correct size.
Fine grit is first given to chicks, usually made of granite, then larger pieces of grit are given to older birds. They don't have teeth, so this breaks down their solid food. It does not readily break down.
Oyster shell is given as a free choice to layer hens. It is an additional source of calcium for them. Oyster shell does break down, unlike grit, so it's a poor substitute for grit.