I just had to get rid of a dog recently because it killed some of my chickens. She was a smart dog, and didnt just kill the chickens. She caught them, killed them, HID them overnight (I thought coyotes did it) then dragged them out the next day to eat them. I think she hid them in her doghouse, it was the only place I did not look. I had to send her back to the shelter. Luckily, she did not teach our older dog to catch chickens. We had her for 9 months. She's a strange dog, very suspicious of new people, even after she seems to already accept them, she might still growl. She's still waiting to be adopted.
poor chickens and poor doggy...she probably had a "ruff" life before you adopted her.