Don't believe him? Go scour YouTube and prove him wrong. You won't find a single such cow-tipping video for a simple reason: physics.
It would be virtually impossible for a single person to dig in a shoulder and tip a cow, and almost as impossible for two or three.
Physicists who studied the matter thought that six people might be able to get the job done.
Still don't believe him? Talk to actual dairy farmers, as he does, and they'll clue you in: Cow tipping is an urban legend, rural-style.