The Levis System was developed by Dr. Don Levis at the University of Nebraska. The basic concept is housing of sows and boars in separate rooms. To heat check, sows are walked into the boar room. Because they have not been exposed to boars on a continuous basis, sows in standing estrus will “lock up” immediately because they are more sensitive to boar stimuli. Pens or stalls may be used for gestation housing.