My Labrador killed two of mine trying to retrieve them for me when I first got them. Basically I took him out to the chicken run and every time he showed interest in them, he got reprimanded. He's a smart dog and eager to please so it did not take long for him to learn he is meant to ignore them. He still chases squirrels, wild birds, rabbits, etc, but he now knows chickens, even chicks, are off limits.
ETA because of what another poster mentioned, being a hunting dog he was already well trained in basic commands and what "leave it" means. Always always always start with the basics and in addition to the one mentioned you need a recall command such as "here", and it needs to be enforced. Yelling and hollering is easy to ignore when there has never been training with enforcement (which can also be said about some people's kids lol).