This was the same area around Nederland I was hiking in a few weeks back, while toting a 12-gauge shotgun and a .45LC revolver to guard against mountain lion attacks. While I knew then that it was perfectly kosher to kill wildlife in defense of yourself or a third person, I'm stunned that only livestock is explicitly covered by the exception and not other living property. Because this happened on a ranch, I'm sure the shooter and his family will be able to argue that a dog is a livestock animal; even then, it certainly sounds like he'll be able to argue that it was just as much of a threat to his whole family around the dog and would've attacked after it was done with his pet.
They made it sound on the local Denver news tonight that the forest service rangers dealing with the incident were looking for a way to not give him a ticket, but that if they did, it could top $1300. All this comes admidst a tree-hugger campaign to prevent the gray wolf hunt in the mountains this fall/winter... with this being the eleventh attack in the Nederland area this month, they should open up a cougar season as well.