Winter feed for layers

So I'm in coastal Maine where the winter weather is not as severe as it is up north and inland, but can still get down to 10 below or less, with a couple of stretches of a week or more where the highs won't go above 20-25.

As far as their combs, all my birds are good for winter -- BO, BR, WW and red and black sexlinks. All but the sexlinks are loose-feathered birds, so they'll be fine as far as the temps. The sexlinks are of more concern. I'm sure they'll be fine, but wondering how I might change/supplement their feed to ease any stress from the cold.

But what would I add, protein or carbs, to let them make more metabolic heat for themselves? Most layer feeds are 16% protein, I've found one from Blue Seal that is 17%. If protein would help I could mix the layer feed with something of higher protein. If carbs are the answer, I could add cracked corn or scratch to the layer feed. Could go either way, supplementing either with oyster shell to keep the calcium up in either case.

Thoughts?