From my husband who grew up on a dairy farm:

Cow tipping is a joke. It does not exist. There are a couple of reasons why cow tipping doesn't happen:

1. Cows sleep lying down.

2. Cows are too heavy for a group of people to push over.

3. If you try to push one over, she will move out of the way.

4. Attempting to tip a bull is hazardous to your health. (Make sure your life insurance premiums are paid up.--seriously...)