The study was conducted at the University of Minnesota's West Central Research and Outreach Center, Minnesota of the United States. All sows (Yorkshire × Landrace) were housed in groups of 15 on a straw-bedded barn during gestation. Sows farrowed in two farrowing barns: a group-farrowing barn and a confinement-farrowing barn. In the group-farrowing barn, eight sows from one gestation pen were housed in one of the three identical rooms. Each farrowing room (9.8 m × 11.0 m) was equipped with two feeders (four feeding spaces each) and two cup-drinkers in a communal area on solid concrete floors that were bedded with wheat straw to a depth of about 0.15 m. Eight individual pens (1.8 m × 2.4 m) bedded with straw were presented in each room during farrowing. Sows farrowed in pens of their own choice. An open door (0.66 m × 0.75 m) was installed at the center of the front panel of each pen, 0.27 m above the floor. The door allowed the sow to exit and enter the pen freely. After farrowing, piglets were prevented from leaving the pen by a low barrier installed at the bottom of pen door (0.40 m above the floor). Sows could step over the barrier without any difficulties. Farrowing pens were removed at about 10 days after farrowing so that sows and their piglets within each room mingled in a large group on bedded floors. Piglets were weaned at 5 weeks of age by removing the sows in the group-farrowing barn. Piglets remained in the same farrowing room until 8 weeks of age, and at that time average group size was 81 ± 2.6 (Mean ± S.D.) in each room. In the confinement-farrowing barn, sows farrowed in individual crates on plastic-coated woven wire floors. Piglets were weaned at 5 weeks of age by moving these piglets to a confinement nursery barn. In the nursery barn, piglets were mixed in pens of nine (four females and five castrated males) on slotted plastic floors and remained there until 8 weeks of age.