I've had slaughters by dogs (my own, sadly) but by far the worst was raccoons. They wiped out 30 of my 40 chickens in a few weeks. Once they got going, they were almost impossible to stop. They started coming out earlier and earlier to get the chickens before the coop was closed for the night. We even came home before dark to see dead bodies everywhere. They also killed off all our turkey poults.
Raccoons, here in the Texas Hill Country, are by far the worst!
I have to say, we do have our fair share of red tailed hawks, owls, possum, fox and coyote. We even have a few Mountain Lions roaming out here, but only the raccoon regularly causes problems, even in town!