Brahmin
The resulting radiation from the Great War caused cows to mutate into the two-headed Brahmin. They are very common across the wasteland and are bred for their hides and their carrying ability.
Brahmin can be found in the wild and in the pens of most major cities. The brahmin herder near a pen will offer to pay you for shit shoveling as well as buying and selling brahmin.
Using a rope, a wild brahmin can be captured similar to the way slaves can be taken except that you do not need to knock brahmin unconscious to capture them. If you attempt to use a rope on a brahmin to capture it, and you fail, it will attack you, but even if that happens you can keep trying to use the rope on that brahmin and he will stop attacking if you succeed. They can then be sold to traders or kept as companions. You can also give or sell them to other players.
They are mostly used for their high carry weight, especially when mining because these materials are extremely heavy.