The only thing I know about cod liver is it is great for feathers and the omega 3's are awesome, i found out about it from some girls website wheres she talks about using it for her modern games, which have incredibly dry feathers like black rosecombs like i have, (my reason for the search), you mix it in with the feed, not sure the amount, but works wonders for this problem, you can also put it on the feathers, problem is the stuff is expensive and it smells VERY fishy, but like I said, works insane wonders-