My 4 and 5 wk old chicks are in a brooder with a dirt floor (a small greenhouse in my garden, actually). Ants, worms, spiders, etc., occasionally pass through and become treats. I put a bowl of oyster shell in there for the chicks to have as grit, but someone just told me they don't need it, that it might actually cause problems... I'm tryin' so hard to do it all right... Could I get a second opinion? Is oyster shell for my little ones actually a bad idea?