Can you de-sensitize a terrier to small animals?

I have a Parson russell terrier male dog who is nearly 2 years old but i have only had him for 6 months. Recently whilst i was out the dog pushed past someone at the door and killed one of my hens. He gets very excited at the sight of the hens and shakes with anticipation. I understand that hunting small animals is bred into them and would like your opinion on whether or not to keep the dog and try to correct his behaviour or to re-home him for his welfare and my existing animals welfare?