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Extended Withdrawal Needed to Avoid Penicillin G Residues

3 September 2013, at 6:13am

US - A minimum 51-day withdrawal is necessary if penicillin G is used in pigs destined for processing, according to the American Association of Swine Veterinarians (AASV).

The USDA’s Food Safety and Inspection Service (FSIS) recently validated its testing methodology to enable the identification of penicillin G procaine in edible tissues at processing, according to Dr Harry Snelson of the AASV. This has resulted in an increase in penicillin residue violations in cull sows. These violations raised the concern of pork producers and veterinarians because many of the violations occurred even though the producer was following the prescribed withdrawal period. The AASV, in collaboration with the National Pork Board (NPB) and the National Pork Producers Council (NPPC), has been working diligently with FSIS and the Food and Drug Administration (FDA) to try to understand what is causing this increase in penicillin violations.

Penicillin G procaine remains an effective treatment in cull sows. It is relatively inexpensive and can be purchased over the counter. It is most often administered intramuscularly at an extra-label dosage of 33,000IU per kg for three consecutive days. The Food Animal Residue Avoidance Databank (FARAD) recommends at least a 15-day withdrawal to allow the drug to clear the tissues prior to processing.

The first challenge with penicillin G is that in swine the FDA established a zero tolerance for penicillin residues in edible tissues. This means that any detectable level of penicillin G in the edible tissues of swine is a violation. FSIS samples both muscle tissue and kidney. Both are classified as edible tissues by FSIS and thus eligible for testing.

According to Dr Snelson, the NPB funded a study at USDA’s Agriculture Research Service to investigate the withdrawal time needed to ensure a zero tolerance for penicillin G in cull sows. The investigator, Dr David Smith, used a dose of 33,000IU per kg for three days with various injection strategies. His findings, described in this presentation from the World Pork Expo, indicate that the FARAD recommendation of 15 days is adequate to prevent violative residue levels in muscle tissue. Unfortunately, the drug is depleted from the kidney much more slowly. He estimates it would require at least a 51-day withdrawal period to ensure that the kidney is free of violative residues at a 25ppb level of detection or 47 days at a 50ppb level of detection.

AASV, NPB and NPPC are engaged in on-going conversations with FDA and FSIS regarding possible remedies for this issue and we will keep you informed as these discussions move forward. FDA has agreed to consider establishing a threshold other than zero for swine. We have also asked that FSIS consider declaring all sow kidneys inedible since cull sow kidneys are not used for human consumption in the United States. This would make the kidney ineligible for testing. This option is still under consideration.

So, in conclusion, at the time of this writing, Dr Snelson states it appears that at least a 51-day withdrawal is necessary if penicillin G is used in swine destined for processing.

For a more thorough explanation of this issue, he recommends reading the 'Advocacy in Action' column in the November/December 2013 issue of the Journal of Swine Health and Production.

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