I've read hundreds of posts and articles about what peop;le feeds their ducks but I still have to ask.... Does anyone give their laying ducks Purina Layena crumbles? Do they need oyster shell? If they do, how do you offer the shell? Do they need anything else on a daily basis? I treat my girls often with romaine lettuce and chopped tomatoes but not daily. They are free range with plenty or bugs, grass and weeds. Thanks!