Interaction of oxytetracycline and bacterial collangenase in the treatment of bovine retained placenta

Retained fetal membranes (RFM) is a postpartum disease that can negatively affect fertility and milk production in the dairy cow population. This disease predisposes the cow to postpartum metritis. Injections of bacterial (Clostridium histolyticum) collagenase have been shown to be highly effective in detaching RFM. Therefore, a combination therapy for RFM and prevention of metritis was hypothesized. This involved mixing collagenase with oxytetracycline, an antibiotic used frequently to treat metritis. However, it has been reported that tetracyclines inhibit collagenase activity. Inactivation of collagenase by oxytetracycline needed to be determined. To test for inactivation of collagenase, isolated bovine placentomes (metabolically active) were infused via umbilical vessels with a mixture of collagenase and oxytetracycline. Eight experimental groups were used: group 1, saline controls; group 2, collagenase 1200 units (U)/ml; groups 3, 4, and 5 contained 1200 U/ml of collagenase plus oxytetracycline (1 mg/ml, 0.1 mg/ml, 0.01 mg/ml, respectively); groups 6, 7, and 8 contained oxytetracycline at 1 mg/ml, 0.1 mg/ml, 0.01 mg/ml, respectively. After 5 h of incubation in a warm (39°C) water bath, manometric pressure (pressure needed to separate cotyledon from caruncle), hydroxyproline (collagenolysis), and total protein (proteolysis) were determined. The antitumor antibiotic doxorubicin was used as a positive control for oxytetracycline. Doxorubicin has been reported to inhibit bacterial (C. histolyticum) collagenase. Experiments with doxorubicin were performed the same as experiments with oxytetracycline except that six groups were used instead of eight. Group 1, saline; group 2, collagenase 1200 U/ml; groups 3, 4, and 5 contained 1200 U/ml of collagenase plus doxorubicin (0.04 mg/ml, 0.02 mg/ml, and 0.01 mg/ml, respectively); group 6 contained doxorubicin at 0.02 mg/ml. It was also the purpose of this study to determine if oxytetracycline residues were present in milk and blood of cows given umbilical injections of collagenase (2 x 10⁵ U/L saline) plus oxytetracycline (0.1 g). This combination therapy was administered to cows that had retained fetal membranes after natural delivery and to cows that had undergone cesarean sections. Samples of blood and milk (when available) were obtained and analyzed for oxytetracycline residues using Bacillus stearothermophilus disc assay.

It was concluded that neither oxytetracycline nor doxorubicin inhibited collagenase in the bovine placentome. All milk and blood (plasma) samples tested negative for oxytetracycline residues.