How do you stop a puppy from killing chickens?

The pup needs to understand that the birds/flock are yours. You are the puppies Alpha and the birds are your property. Not unlike training a pup not to chew shoes, careful watch must be taken for the first few weeks of training and sharp commands of "NO" when the pup chases the birds. Take the pup around chickens as often as possible and make it feel the flock is part of the pack. Mistakes will be made but if you are watchful and you use a leash for the first few days most dogs will come to accept the birds without seeing them as prey.