In the 1980s, Swedish swine producers were forced to develop several production models to remain profitable due to the strict legal policies facing the swine industry. By 1994, approximately 150 Swedish farms were using a sustainable model for pig production. This model, a deep-bedded, group housing system for pregnant, farrowing, and nursing sows and their litters, was known as the Västgömodel. Ljungström and Thorstensson are two versions of the Västgömodel system. In the Ljungström system, sows farrow in conventional pens and are moved with their litters to group nursing rooms after the pigs are 10 to 14 days old. In the Thorstensson system, sows farrow in group nursery rooms in temporary wooden farrowing boxes, which are removed after the pigs are 7 to 10 days old and have begun to climb out of the boxes. Group lactation ensues.