The only reason why this dog was not wearing a muzzle when I was training her was because I had complete confidence that I could stop the dog from killing the chicken. After the dog understands not to kill the chickens in your pack continue training the dog to reinforce the desired behavior. If you are introducing new chicks or new adolescent chickens to your pack you should retrain the dog not to kill those chickens as well. The dog might not associate the new chickens or new chicks as part of the pack. So make sure that every time you introduce new chickens to your pack to retrain your dog. A dog like the one I was training in this video is a hunting dog and is used to track and kill small game. It was bred for hunting and kills small rodents regularly. For a dog like this one you must constantly reinforce the behavior of submitting to the chickens. Good Luck!