I just wanted to reply to the OP. I completely understand where you're coming from, in wwondering who to call and not wanting to go knocking.
Near where we live, there is a guy that keeps cattle that get out all the time. I mean, he makes the news every month or two. The sheriff was getting pretty annoyed at needing to come out and get cows out of the road (safety issue) and the guy couldn't care less apparently. We had never paid attention to the exact area this is, it's "nearby" in a country kind of way-as in, same county.
One day last year, we were driving down a country road, and...hey, is that a COW in the road? Yup, sure is-and there's a bunch more all over the place nearby-obviously, they broke out. We checked around, tried the closest house, no answer. Saw someone down the road a bit checking their mail, so we went and talked to them. Turns out it's good no one was home, she said he probably would have answered the door with a .22 in hand. And yes, they are his cows and she'll call the sheriff. They get out all the time, he doesn't care. Oh, hey, looks like we found out there the guy with the cows that make the news lives.
Long story short, some people really don't care, and sometimes it's not the best thing to go knocking on their door. I doubt he would have fired the gun, but still. In our case it was a public safety issue so the sheriffs would have been the ones to call. In the OP's case, the SPCA locally handles farm animal cases as well, so they would have been the ones to call-and if they felt they would be threatened, they would go with the sheriffs. It does vary by location though-I would probably have started with the local animal control/humane society. Sheriffs pretty much do the public safety thing, and unless the cow was presenting a public danger, I don't they would do anything. Unless the person is already on their radar, and that just gives them ammo.