The swine industry continues to change, but the rate of change appears to be' increasing. The number of farms with hogs declined dramatically in the last twenty years. Nationally, in 1991, there are only 30% as many farms with hogs that existed in 1970 (Figure 1). Midwestern states, and Iowa in particular, fared better than the national total, losing "only" 60 percent of the hog farms. While farm numbers decline, the number of hogs produced in the U.S. remains relatively stable. As a result, the average number of hogs per farm has doubled nationally in Iowa and most other Midwest states. In contrast, North Carolina has had an eight-fold increase in the average number of hogs per farm in 20 years.
Lawrence, John D., "The U.S. Pork Industry In Transition" (1992). Economic Staff Paper Series. 239.