They just DON'T stand up to a CX.
The first thing I noticed about CX were the massive size of the legs on the chicks. I was all ways told a puppy with huge paws made a big dog.
I'm THINKING this holds true with chickens too.lol
About a third to a half of my CX's diet is a combination of sprouted grains (barley, wheat and sunflower seeds) and old garden produce. I kind of throw it around their yard to provide "forage" since I live in a semi-desert and I can't do all that cool pasture raised stuff. I had not thought about the protein angle. I just give it to the birds because it's so much cheaper then store feed and gives then something less calorie dense to eat.