Snail shells instead of Oyster shells?

Hello

We have a MASSIVE number of small snails in the garden. My morning routine is to pick the snails off my vegies and then crush the snails (I have a special crushing brick and tray in the chicken coop!) and the girls munch them up for breckie before heading out into the garden. I do not provide them any oyster shells as I figure the snail shells will serve the same purpose. We have great eggs with nice thick shells and the girls seem happy. The snails would give them a good protein boost as well I suppose. Just wondering if anyone else does this and what your thoughts are?

Also I have read in some forums the concern that some snails may contain harmful parasites (we're in Australia), but because there are so many snails around I don't think I'll be able to prevent the chooks from eating them on their own anyway. The less snails the better I say!

Many thanks for any feeedback.