OXYTETRACYCLINE RESIDUES IN MILK AFTER INTRAUTERINE TREATMENT OF COWSWITH RETAINED FETAL MEMBRANES

Objective-To establish the maximum concentration and duration of oxyte tracycline residues in milk from cows with retained fetal membranes gi ven the antimicrobial via intrauterine infusion, and to investigate wh ether the number of infusions or the presence of fever (> 39.7 C) affe cted the duration of residues. Design-Prospective study. Animals-54 Ho lstein cows with retained fetal membranes on a single 1,400-cow commer cial dairy. Procedure-Cows were treated once a day with 5 g of oxytetr acycline (50 mi of 100 mg/ml solution in a povidone base) by intrauter ine infusion for at least 2 days. or until the membranes were expelled . Cows that became febrile (rectal temperature greater than or equal t o 39.7 C) were also given 20,000 IU of procaine penicillin G/kg of bod y weight, IM, for 2 to 4 days. Milk samples were collected at 24-hour intervals during treatment, and at 12-hour intervals after the last tr eatment. All samples were frozen and submitted every 2 weeks for high performance liquid chromatography analysis for oxytetracycline. Result s-Oxytetracycline was detected in milk of all cows during treatment, a t a maximum concentration ranging from 47.2 to 1,804.6 mu g/kg (mean, 316.9 mu g/kg). Duration of oxytetracycline residues after the last in fusion ranged from 0 to 144 hours (mean, 52.3 hours). Neither the numb er of infusions received, nor development of rectal temperature > 39.7 C, affected the maximum concentration or the duration of oxytetracycl ine residues in milk. Clinical Implications-Milk obtained from cows th at had been treated for retained fetal membranes by intrauterine infus ion of oxytetracycline should be discarded to avoid illegal residues.