Chance,

Yes, those fallen celestial beings are probably the ones perpetrating those horrific acts against cattle.

I have wondered for years, why they would do that.

They probably already are quite advanced in knowledge and science, so I don't think that they are trying to learn basic things.

Or are the cruel and sadistically insane, like Dr Mengele?

Or are they simply showing their rebellion against the LORD, and hatred for him, via hating his physical creation?