The slaugtherhouse pen is a building in Modoc.
This is where all of the brahmin are kept and slaughtered. It is possible to be very animal friendly and free the brahmin from the pen, but reputation with Modoc will take a hit.
A slaughterhouse where brahmin are being killed for hides and food. It is run by Biff, Grisham's brother.
The slaughterhouse pen appears only in Fallout 2.