Urine sampling can reliably detect penicillin residues in sows

Urine sampling is a reliable way to detect procaine penicillin G (PPG) residues prior to processing and may help producers avoid processing-plant violations, according to Locke A. Karriker, DVM, a professor at Iowa State University.

Increasing incidence of PPG-residue detection in cull sows has been reported, due in part to changes in the PPG-testing method made by USDA’s Food Safety Inspection Service in 2011.

Residues of PPG in sows are not uncommon at processing. Although plasma concentrations of PPG correlate well with tissue residue, collecting and evaluating plasma is complicated, says Karriker in a Pork Checkoff report.¹ Urine is easier to collect and handle.

PPG residues are most often found in sows if extra-label doses of PPG have been administered or if treatment was continued for more than 3 consecutive days, he says.

Karriker designed a study involving 47 sows, with three treatment groups:

• Group 1 received the labeled dose of 3,000 IU/lb (3 mL/lb).
• Group 2 received an average volume of sterile solution once a day for 3 days.
• Group 3 received an extra-label dose of 15,000 IU/lb (15 mL/lb) once a day for 3 consecutive days.

Karriker found PPG residues persist longest in injection-site tissues — for at least 28 days after PPG administration. It stays in the skeletal muscles for 14 days. PPG depletes faster from the kidneys, and residues can be found for up to 6 days after administration to the sow.

Sampling the sow’s environment was not reliable for determining residues. While PPG residues were easily found in the environment, they did not correlate with tissue residues, Karriker says.

The current withdrawal time for PPG is 7 days. Although a 15-day withdrawal time has been proposed by the Food Animal Residue Avoidance Databank, it may not be sufficient to avoid processing-plant violations, Karriker says.

¹ Karriker LA. A study to correlate procaine penicillin G in tissues, plasma and oral fluids of sows and determine environmental transfer of penicillin to untreated sows. Pork Checkoff. http://research.pork.org/Results/ResearchDetail.aspx?id=1920