Animals were from a privately owned, 1500-head sow farm that was willing to participate and sign a consent form. The herd was representative of generally healthy, well-managed, modern swine production. Monthly blood samples collected from gilts and piglets and submitted to the University of Minnesota Veterinary Diagnostic Laboratory tested negative by polymerase chain reaction for porcine reproductive and respiratory syndrome virus and positive by enzyme-linked immunosorbent assay for swine influenza virus and Mycoplasma hyopneumoniae. Piglets were weaned twice weekly at approximately 21 days of age to an off-site continuous-flow nursery managed all-in, all-out by room. After a 26-day nursery period, pigs were moved to on-site finishing barns. None of the facilities employed bio-aerosol filtration, but all were shower-in, shower-out.