A chopper unit for chopping bales of vegetation is particularly well suited for chopping large square bales. The chopper unit mounts on the arms of a transporter unit such as a skid loader. The unit includes a housing having a deck with a window therein. During normal operation, the deck faces upwardly. The housing includes a chopping chamber having the window in the deck at one end thereof, and extending to an opening or window in a side wall of the housing. A bale hopper mounted on the deck can translate along a predetermined path. The bale hopper extends generally upwardly when the unit is in an operating position, and surrounds the window in the deck. A vegetation cutter mounted within the chopping chamber partially projects through the deck's window and into the hopper. Rotating the cutter chops the vegetation into small pieces. The hopper translation allows the cutter to access the entire bottom surface of the bale. A fan preferably forces air into the chopping chamber adjacent to the cutter to sweep chopped bale particles to an opening in a wall of the housing.