I have both a herd dog and a bird dog, Blue Heeler and English springer spaniel. Both do fantastic with the chickens (and other pets). The spaniel completely ignores the chickens but the Heeler treats them as if they are "family" and she's gentle around them. She can be running across the yard but will stop and walk through the middle of the flock so she doesn't' spook them. She even makes a effort to look away from the chickens, no eye contact, as she walks through the middle of the flock.
I've even had a case of a coturnix quail getting loose and flying across the yard. The heeler chased it as if I had thrown a tennis ball. I thought for sure the quail would be killed, but she grabbed the quail and brought it back to me, barely a wet feather. She watches the free range chicken chicks but I think that's guarding, she makes no move to chase or scare them.
I've never lost a chicken to the dogs or the cat.
I did make a introduction to the dogs with chicks. I wanted them to know the chicks are family too and should not be bothered. I've never had to correct the dogs though other than saying the spaniels name when she scatters the chickens by running through them. Springers can be excitable.