I think this has been an ongoing debate for ages. I know forums I am attached to, people I speak to have very firm opinions on what is ok and not ok to feed your birds. For example there is a debate regarding the feeding of eggs. Some say the egg shells are a great source of calcium. I personally wash them out, boil them and grind them up, many say boiling them tricks the chickens and they have no idea they are eating egg shells. Others say this will cause your birds to eat their own eggs. The whole time I was feeding my chooks egg shells I never had a problem with them eating their own eggs. Was I lucky? I guess it is up to the individual. However I know I will be feeding my new birds egg shells once I have them. I see no point buying oyster when according to many egg shells provide the same calcium required. Besides I hate throwing anything out and this way, every part of the egg is used.
Anyway I found this article and thought it was extremely interesting, not saying you should all follow it and everyone entitled to their own views but I found it a good source of information