The U.S. hog industry has experienced dramatic structural change as the trend continues for fewer producers with increased enterprise size. Through intensive production practices, efficient use of inputs, and improved disease control measures, large producers have attained more production per sow, more production per unit housing, and lower feed costs (VanArsdall and Nelson 1984), Pork production has also become less seasonal with the adoption of capital-intensive confinement units. Thus, pork production has become increasingly dominated by enterprises that produce hogs on a year-round basis in a confined environment.
Skold, Karl D.; Grundmeier, Eric; and Johnson, Stanley R., "CARD Livestock Model Documentation: Pork" (1989). CARD Technical Reports. 3.