I have been providing oyster shell for my ducks (hens only) since shortly before they started laying. I get Purina Oyster Shell and it's fairly large chunks...seems to me anyway. There never seems to be any gone for the dish. Not sure if it is too large, the one hen I have that is laying doesn't need it, or what? Also, if it is not being eaten, does it need to be dumped and replaced every day like feed? Wouldn't think that would spoiled, or be harmed by getting wet, but not sure. Been dumping it just in case, but wondering if I am wasting it.