Sows are typically treated with about 5 times the penicillin G procaine dose that is used for growing swine. Producers, with the advice and consent of a consulting veterinarian, can legally use this dose in an "off-label" manner provided a proper pre-slaughter withdrawal time is selected. Unfortunately, there are very few data which describe the depletion of penicillin residues from sow tissues under such use conditions. Although, Apley et al. (2009) did conduct a trial in which heavy sows were dosed with a 5x penicillin G procaine dose, the pre-slaughter withdrawal periods selected (2, 4, 6, and 8 days) were too short to properly model penicillin G residue depletions from kidney, muscle, and injection sites. Thus, the study of Apley et al. (2009) was not able to provide producers with a definitive withdrawal period for penicillin G procaine use in sows. Because a new regulatory method has been established, and because rates of penicillin G procaine depletion are poorly defined in swine, a residue study employing both the regulatory screening method and the regulatory confirmation method (LC-MS/MS) is needed to provide definitive withdrawal periods for penicillin G procaine in sows. <P> Specific objectives of the proposed research include. 1) determine the appropriate pre-slaughter withdrawal period for penicillin G procaine in sows under practical use conditions; 2) determine whether the pattern (sites and volume) of intramuscular penicillin G procaine administration influences penicillin G procaine depletion from edible tissues of sows; and 3) determine the incidence of false-positives returned by the Charm-KIS microbial inhibition test under controlled conditions.
Heavy sows (<400 lb) will be treated with a 5x penicillin G procaine dose via intramuscular administration on 3 consecutive days. Three patterns of drug administration will be provided to three separate groups of sows: Treatment 1) A maximum injection volume of 10 mL will be administered to sows, but within day, multiple injections will be made into a single muscle group to deliver the total required drug volume (5 mL/100 lb BW); Treatment 2): A maximum injection volume of 10 mL will be administered, but within day, multiple injections will be made to separate muscle groups to deliver the total required drug volume (5 mL/100 lb BW); and Treatment 3: A maximum injection volume of 20 mL will be administered to sows, but within day, using multiple injections will be made to separate muscle groups to deliver the total required drug volume (5 mL/100 lb BW). Sets of 9 hogs each will be slaughtered at 5, 10, 15, 20, 25, 32, and 40 days after the last drug administration. The study will be replicated twice for a total of 126 treated sows. Kidney, muscle, and injection sites will be analyzed using qualitative (microbial inhibition) and quantitative (LC-MSMS) methods approved by the FSIS. Residue depletion data will be plotted with time and withdrawal periods estimated using established methods.