I hear a lot of suggestions about ways to "increase protein" but while well-meaning, most times they are misguided. Keep in mind that anything you do to increase ingestion of one nutrient, interferes with the ingestion of another. IMHO, the best thing to do is stick to a nutritionally balanced pelleted feed, and trust that the feed companies - who have sunk a lot of money into researching the nutritional needs of the animals for whom they are making feeds - know what they are doing (because if they didn't they'd go out of business).
For example, my flock gets good quality layer pellets (16%) in the time of year they are laying and not molting. As they stop laying to molt, I switch to an All Flock formula (18%) as the additional protein helps them to regrow their feathers, while also offering the balanced nutritional diet they need.
At all times they have access to many acres of free range, fresh water, and oyster shell.
If I were to add an additional source of protein (I've heard suggestions ranging from cat food to peanut butter), I would be introducing a food that is NOT nutritionally balanced for chickens. While filling up on this protein source, they are missing out on the other things they need to fulfill their balanced diet, so in the end I'm not doing them any favors.
