I just recently got my chickens and I have two dogs, a chihuahua and a black lab/hound mix. My chihuahua got very excited seeing my young girls, little chicks, whimpers and whines when he sees them. He ran at the older chickens a couple of times, then saw that they are bigger than him and quit. My lab looks at the babies, cocks his head picks up his ears and watches....with the big hens we had an interesting event. The day I brought them home I was taking them from the traveling pen in the truck and putting them one by one into the nests, one hen got loose and of course I couldn't catch her, but Buck (my lab) was watching her closely, so I thought I'd give it a try, I told him "get her" and he chased her into the horse pen, I told him stop, and he did. He proceeded to herd that lone chicken back to the coop listening to my commands, never bit at her or tried to, turned and trotted back to me when she went into the coop. Please don't misunderstand, at no point did I believe that Buck would hurt the chicken, he's the type of dog that a small child, my grandson, can sit on, pull his ears, tug at his mouth or pull his tail and even kick at and Buck doesn't budge, fuss or even look in the direction of my grandson. My dad had a fox terrier that never chased the chickens we had when I was younger, but my Sheltie did chase and did kill one (happened to be dad's favorite, a polish hen). So I think it depends more on the prior obedience training your dog has had and maybe some breed history/use could play a part. My lab, lots of obedience training, same for the fox terrier, the sheltie didn't have much training/manners, and the chihuahua I think just figured he doesn't want any part of something that outweighs him. On another note, my lab loves "cleaning up" behind the chickens, which has prompted me to buy charcoal biscuits for his treats. When I catch him at it and get onto him, he sulks away as though I have ruined his whole day.