16% vs. 19% protein layer feed

[Chris09]

I have just noticed that my two biggest, most mature cockerels are feather-picking the other birds (picking feathers off the back of the neck and eating them). I have read a few posts here on it, and I couldn't tell from those whether this is just a bad habit, or is almost certainly a sign of some nutrient deficiency. Any ideas on this. They do get all the chick starter (20% protein) they can eat, plus free range on good pasture. Is it possible they are eating too much from the pasture, and not getting enough protein?

Have you treated for lice/mites, if so what did you use?
The feed that your feeding now, does it contain animal proteins?

Keep in mind it's not all about the protein amount, more so it is the type of protein and the amino acids that make up a set amount of protein.
Ive seen chickens do far better on a good 15% protein with animal proteins in it than ones on a 20% protein feed that is vegetarian based. Chicken will find animal proteins any way they can and if that means feather eating then they will eat feathers. (also feathers are a lot easier to get than bugs when it comes to chickens)