Antimicrobial drugs are fed to hogs at sub-therapeutic levels to prevent disease and promote growth. However, there is concern that the presence of antimicrobial drugs in hog feed is a factor promoting the development of antimicrobial drug-resistant bacteria. This study describes the extent to which antibiotics are used in hog production and how this changed between 2004 and 2009. This study also uses a sample-selection model to examine the impact that use has on the productivity of U.S. hog operations. Using hog producer data from 2004, the analysis did not find a relationship between productivity and sub-therapeutic antibiotics fed during finishing, but productivity was significantly improved when fed to nursery pigs. These results are being evaluated using similar data from 2009.