I don't know, maybe they would understand Fluttershy gave birds worms in Dragonshy episode. So maybe they would understand but we aren't talking about worms, lol. We're talking about making some burgers, so they might not accept us for that.
It would probably be hard to kill cows. I mean, cows in MLP actually talk and communicate with the ponies. They have an intelligence that is probably equal to that of ponies.