The USDA’s Food Safety and Inspection Service (FSIS) has recently reported a number of penicillin G violative residues in sows presented for processing. Historically, the U.S. swine industry has experienced extremely low levels of antimicrobial residues detected at slaughter, so this occurrence raises concerns regarding the timing of antimicrobial use in sows intended for processing and the testing methodology currently being used by FSIS.

At this time, the American Association of Swine Veterinarians (AASV), the National Pork Board (NPB) and the National Pork Producers Council are working with FSIS to better understand the testing methodology currently in use to determine if extended withdrawal periods will be necessary to ensure compliance with the zero tolerance level applied to penicillin. These groups have also been in contact with one of the major penicillin manufacturers to inform them of the recent findings and discuss any necessary changes to the withdrawal recommendations.

Veterinarians should consult with their clients to ensure they are following appropriate withdrawal periods when using any antimicrobials in swine shipped to market including cull sows and boars. With regards to penicillin use, be sure to remind producers that:

  1. Penicillin G is only approved for use in swine for the treatment of erysipelas;
  2. The labeled dose rate for penicillin G is 3000 units per pound of body weight (1 ml per 100 lb. of body weight);
  3. Any use for other indications or at a different dosage rate would be considered extra-label drug use and can only be done under the direction of a veterinarian as outlined in guidelines for extra-label drug use;
  4. Extra-label use also requires the application of an extended withdrawal period which may be difficult to achieve with cull animals; and
  5. Long-acting pencillin (penicillin G benzathine) is not approved for use in swine and, thus, any use would be considered extra-label.

The Food and Drug Administration-approved withdrawal period for penicillin G at the labeled dosage is seven days in swine. However, the AASV and the National Pork Board have historically recommended an extended withdrawal period of at least 14 days to meet export requirements. Also note that the recommended voluntary withdrawal period for long-acting penicillin is 50 days to meet export requirements. A database of recommended withdrawal periods for export can be found on the NPB Web site: (http://www.pork.org/Resources/214/MaximumResidueLimits.aspx