Our goats were killed during the winter by a bear. Our goats were 200+ lb. nubian wethers and the bear was able to take each down and dragged one about 50 feet into the woods. We later saw that bear and he is absolutely huge. A couple days after killing our goats, he appeared down the street from us, killed a couple more goats and tried to take out a miniature horse before getting shot. He managed to survive the gunshot wound, but I don't think he'll be around long if he keeps killing off livestock.
Coyotes, dogs, wolves, and mountain lions will also kill off goats. Before we had that incident, I had never really thought anything would be able to kill our goats!