Prophylactic antimicrobials administered in rams before elective castration are detectable in resected tissues and unlikely indicated under aseptic conditions.

Objective: To report the incidence of intraoperative surgical site positive bacterial cultures and occurrence of postoperative infection following elective castration in rams and to measure, in different units, the concentrations of benzylpenicillin, ampicillin, and oxytetracycline in resected tissues following preoperative SC administration.

Methods: In January and February 2016, healthy rams were enrolled before elective castration and were randomly assigned to the control group (saline) or subcutaneous treatment groups (22,000 IU/kg of procaine benzylpenicillin, 6.6 mg/kg of ampicillin trihydrate, or 6.6 mg/kg of oxytetracycline dihydrate administered within 2 hours before resection of the tissues). Excised tissues were sampled to measure drug concentrations by reverse phase high-performance liquid chromatography-tandem mass spectrometry. The surgical site was swabbed at the end of the procedure for anaerobic and aerobic cultures. Rams were monitored for 2 weeks after surgery. The tissues' weight-to-volume ratio in 10 additional rams was measured in May 2022 to allow conversion of drug concentration from ng/g to µg/mL.

Results: No microbial growth or postoperative complications were detected in 46 rams. The concentration of benzylpenicillin, ampicillin, and oxytetracycline was successfully measured in all tissues and reported in ng/mL and µg/mL.

Conclusions: Prophylactic administration of antimicrobials is unlikely indicated for elective castration in rams in a hospital setting. Concentrations of antimicrobials were detected in resected tissues within 2 hours after SC injection. The relevance of the conversion of drug concentration from ng/g to µg/mL needs further investigation.

Clinical relevance: Avoiding prophylactic administration of antimicrobials for elective castration aligns with the principles of antimicrobial stewardship. Without sound rationales, extralabel routes of injection should be discouraged in rams undergoing castration.