Chickens are omnivores like us. They eat meat, vegetables, bugs, grasses, seeds. The feed companies mostly don't put meat products into the feed because in some places they feed chicken manure to cattle, so there is the "mad cow" thing to think of. However, some very small companies will put a little fish meal into the feed. You can feed raw hamburger, liver, tuna, and yes, even chicken to them for extra protein. I would rather they didn't eat mice, but they will 
