There has been at least a decade-long march to improve the health of the US swine industry. This coincided with rapid expansion of many farms and a tremendous change in the ownership structure of the US swine industry (fewer owners having larger sow farms and owning or controlling more pigs). Prior to 1990, the industry consisted of more typical farrow-to-finish farms that would live with chronic diseases such as atrophic rhinitis, Actinobacillus Pleuropneumonia (APP), Swine Dysentery, Mycoplasma pneumonia and a host of enteric organisms. Many of these would persist on an individual farm until either the owner became frustrated, or profitability and production were so poor that depopulation/repopulations were done. This was basically the technology of the 1980s. The late 1980s and early 1990s brought a tremendous amount of new sow farm construction or farm conversion. Nearly all of these were either farrow-to-wean or occasionally farrow-to-feeder pig (25 kg) with off-site finishing. The off-site nurseries and finishers (or recently wean-to-finishers) were built in several different configurations. Some would have 1 week’s worth of pigs on a site, some would have multiple weeks of nursery, some would have multiple weeks of finishing, or some would comingle farms and have only 1 week of nursery or 1 week of finishing on a site.