Firstly let me tell you that the first step to dog training is you should NEVER, EVER have to be physical with your dog. Beating your dog with anything is a good way to cause health problems with your dog, trust issues and get you in trouble with the law.
When you train a dog you use something called positive reinforcement. Whether that be treats or toys. By beating your dog, you are not showing your dog what he is supposed to do, instead he is just getting confused. In order to fix this problem I would leash (and maybe muzzle your dog) and sit with him next to the chickens. When your dog looks away from the birds or doesn't show any signs of aggression: Praise him. Give him treats. Say "Good Boy".
When he does show aggression, say "Eh eh" in a short sharp voice.
If your dog is anything like mine he will stop what he is doing and back up. Always keep him leashed/muzzled until you feel he is 100% okay with the birds.
If you do not want to train him and respect him as a living creature, I would rehome him.