Sentence:  There are three principal feed bunk types for dairy and beef cattle : ( 1 ) Fence-line bunks - cattle eat from one side while feed is put in from the opposite side of the fence by self unloading wagons ; ( 2 ) Mechanized bunks - they sit within the feed lot , are filled by a mechanical conveyor above feeding surface ; ( 3 ) Special bunks - as discussed here , they <WSD>permit</WSD> cattle to eat from all sides . 
Meaning of the word marked with <WSD> tags:  make it possible through a specific action or lack of action for something to happen