I have English Shepherds and they have been very good, but I second the note on training. We had a problem with our female killing chickens last year but were able to retrain her. Her killing was a combination of two things: 1) she was a young herding dog that needed to learn to use a little less force when working with birds and 2) we got a whole bunch of birds from someone and hadn't introduced her to them. She had always been fine with the chickens and we never thought about introducing her to new birds. She killed some of the new chickens, but never touched the old ones.
She's perfectly trustworthy now. In fact, half our flock went into her whelping area and while she chased them all out, she didn't hurt any of them. She helps keep the foxes and coyotes away and even runs around barking at hawks.