My Boxer is fine with the chickens, chicks, and ducks. BUT there is no way in the world I would trust him with them alone... He is sort of odd... no nonsense.. no one plays or he breaks it up, just wants to lay around and keep an eye on things... but it would only take one chicken pecking him and he would sign their death certificate.
My Doberman... well she is just unpredictable as far as little animals are concerned... she loves her cats but birds are to tempting with the noise, and running, and flapping. She mothered a kitten that was 7 weeks old and the size of a 1 week old kitten. She cleaned her, protected her, carried her to her bed and even tried to let her nurse, if any of the other cats got around the kitten she showed them exactly how many teeth she had. With that being said, even if she was being good with the chicks and maybe even trying to take care of them, it would only take one chick/chicken/duck running around making a racket before she snatched them up. For now she watches them through the fence and is getting better about them being out, once she gets good with that I will take her out on a leash with me... and maybe even a muzzle cause she is quick. I don't want her to figure out that it is fun or whatever to chase them. We have had a couple of incidents where I was in the coop with the run door open and turn around and she is right beside me (my son wasn't paying attention and let her in the yard surrounding the coop). I told her out and she went back to the porch... but that still isn't enough to trust her lol. I will never trust her with them alone. Probably the most slack she will get is being able to run around in the yard with the chickens out while I am there... she is very well behaved as far as minding, but in the chase I don't know that she would even hear me. We will just have to see how many privileges she gets. Everything has to get along here, even the cats lay out in the chicken yard while the chickens are out, they got reprimanded when they started to stalk and now I don't worry about them at all with the big chickens, especially since if the cats get to close or don't walk off when the chickens come up to them they get pecked, and then run for their lives with a bird on their heels lol. The chicks are watched like a hawk by me cause they are to small to even begin to defend themselves.
If he were mine and has already killed then if he was allowed near them at all it would be on a leash so I could get control of the situation if I had to, and probably with a muzzle on so he couldn't snag one that got to close.
Good Luck!