Idk about chicken beaks, but cartilage, chicken feet, and their bones are completely digestable. It's actually a lot of the fillers and other things in commercially processed dog food that the dog cannot break down. Dogs cannot break down any sort of plant matter unless it is cooked to literal death, or blended into a pulp. Some vegetables and starches etc no matter how cooked down or processed can't be digested at all, such as corn/gluten of any type etc. I feed my dog a prey model raw diet that I butcher and create myself, so it is pure meat, 80% muscle meat of various types 10% edible bones 10% various organs. His feces is far smaller, less smelly and decomposes quicker on it's own if it is left alone. Honestly I don't worry about keratin levels unless my chameleon is not drinking enough at all and not being fed soft-bodied feeders. In my opinion insects have the ability to have as high a protein as lean beef, because lean beef isn't easily digested by people and insects are easier to digest wholly and easier to absorb proteins from. You can also eat a larger amount of insects than beef.
