Hello, my second topic to this forum, which I quite enjoy.  You're a
thoughtful group.  I raised chickens as a child, and now once again with my
own children I have a dozen layers.  I noticed this winter (Pennsylvania,
USA) that they couldn't forage much so they relied on commercial food,
supplemented with our leftover meat bones and vegetable scraps.  It did not
supply enough proteins, as they started going for each others hind feathers
(a source of proteins).  I confirmed this diagnosis with a retired chicken
farmer.  It started getting vicious.  I examined the commercial feed more
closely, and noticed that the protein was completely soy based!(not so back
in the 50's).  You can fool a human, but you can't fool chickens.  They want
meat proteins.  I switched feeds, but with spring upon us, I won't know
until next winter if this was the problem.  They absolutely prefer any dead
animal or meat scraps over any other food.  Your grocery-store chicken is
likely raised in isolation (no cannibalism possible), so a fat, corn-fed
bird is not a problem to produce.  From my experience there is a huge taste
difference between free-range and 'factory' birds.  My advice - eat free
range, avoid the factory fed facsimile.  Sorry for the long-wind.  It's the
idiot-savant in me.
-Lou Huis