The Brahmin, which are mutated Brahman cattle, have eight stomaches, two heads, and bulls have four testicles. They may be used as pack-animals or for food.
There is an easter egg in Fallout 3, which ables you to tip Brahmins. What you have to do is to crouch and activate any Brahmin that isn't attacking you. What happens is that the mutated animal will moo, and turn into a ragdoll for a short while.