According to ERS (Economic Research Service) report "U.S. Hog Production From 1992 to 2009: Technology, Restructuring, and Productivity Growth", the number of hog farms fell by more than 70 percent from 1992 to 2009 while the hog inventory remained stable.
The average hog farm grew from 945 head of hogs sold or removed under contract in 1992 to 8,389 head in 2009. Specialized finishing operations (feeder-to-finish) increased their share of production from 22 to 77 percent during 1992-2004, while the share of production from farrow-to-finish operations fell from 65 to 18 percent. However, from 2004 to 2009 the shift toward operations specializing in a single phase of production slowed, and farrow-to-finish producers slightly increased their production share over this period. High corn and soybean prices during 2007-09 raised hog feed costs considerably. Declining hog farm numbers during this period suggest that many small, likely high-cost operations ceased production, adding to the average size of hog operations.
October 2013/ ERS-USDA/ United States.