I have 5-7 roosters that need culled! They are RIR, BO, and RIR x BO. All decent size. I would like them to use for grilling, baking and some soups. What is the best age to cull them at for what I want to use them for? Also I was told to use grower/finisher feed for them the last 2-4 weeks of their life because it will make them meat tenderer....any truth to that?