Quite a wild dog. Shouldn't the dude have had a staff if he was guarding the cattle? With a good, sturdy staff he could have pummelled the dog into submission.
@Kaarme Each country has their own custom. In my country, people don't have a staff when herding cattle too. And beating them into submission is not possible. While we call it wild dog, it is nothing like our normal dogs . It is feral and dangerous since they hunt and kill animals. Their bites contain rabies and its pack may had been nearby too. The one that herded the cattle is just a child, his safety is more important.
Or they might just need to hunt down the wild dog with a group of men armed with bows and spears. It seems like a very rare occurrence, since they were unprepared for it. Putting that one wild dog down would probably fix everything. (Well, except for the dead Yak)
@Someguy They just need to give the guy a gun for the time being. The dog will keep coming back as long as there's food readily available. Unless it found an even easier source elsewhere. In the end, for whatever reason, it didn't even start to eat the yak it drove to death.