Storey's book on Turkey has a section on using co2 to kill off birds . I agree with the free range idea, I have a young rooster that is bottom of the chicken pecking order. He was getting beat up all day and I plan on eating him soon but I wanted to have a few birds to do in one day so he gets a few more weeks to go. I just let him go out and free range and he is happy not to be beat up and he is sticking right by the coops and the others look on in jealousy as he scratches for worms and eats greens all day