@vehve Aside from molting, I don't think the protein level needs to change much in winter. The primary thing that needs adjustment is energy.
As for fat, if you're providing some animal based protein, they're likely to get sufficient fat along with that in grains and seeds. For just a few birds, providing animal protein is easier. I use fishmeal to raise the protein in my 16% organic grower feed for young birds and molters. Occasionally I'll grill up some beef or poultry for the chickens but 16% crude protein is what the adult birds get most of the year.
They also get grilled coon and possum.
Roosters do well on about 14% protein.
A couple % points is a pretty big swing in protein for adults. While you're tweaking protein, it's more important to consider the limiting amino acids, while the crude protein may be high in some vegetative sources, they're usually woefully low in Methionine, Lysine and Cystine. Feed manufacturers that use vegetable protein (which is most feed) have to add synthetic amino acids for balance.
See the liebig barrel in the next link.
http://feed-additives.evonik.com/pr...nutrition/animal-nutrition/pages/default.aspx
Excess protein or excesses of some amino acids are excreted as nitrogen and results in more ammonia in the bedding.
As for rapeseed, 80+% of what is available in the US and Canada is GM for resistance to roundup.