Effect of enrofloxacin treatment on plasma endotoxin during bovine Escherichia coli mastitis

Objective and design: To investigate the effect of enrofloxacin on endotoxin resorption during bovine Escherichia coli mastitis. Animals: 12 healthy early postpartum Holstein cows. Treatment: Mastitis was induced by intramammary infusion of 10(4) cfu E. coli P4:O32. Six cows were treated twice according to the usual enrofloxacin therapy: 5 mg/kg enrofloxacin 1) intravenously at 10 h and 2) subcutaneously at 30 h after challenge. The other 6 cows served as non-treated controls. Methods: Blood and milk samples were collected at several time points after challenge. LPS in plasma was quantified using the limulus amoebocyte lysate (LAL) assay. The somatic cell count (SCC) and cfu of milk samples were also analysed. Results: Occasional LPS peaks were detected in the plasma of 2 control cows at 6 h post-challenge and of 1 enrofloxacin-treated cow at 10 h post-challenge (P < 0.01 and P < 0.05, respectively, in comparison with time 0), just before enrofloxacin treatment. After enrofloxacin treatment, no significant LPS amounts were detected in the plasma of treated cows, but neither in the control cows. Conclusion: During induced coliform mastitis, LPS resorption in plasma occured only sporadically and within 10 h post-challenge. Whereas enrofloxacin treatment clearly limited bacterial growth in milk, significant effects on LPS resorption could not be detected. This suggests that enrofloxacin treatment of E. coli mastitis is predominantly beneficial by its bactericidal activity and is not associated with enhanced resorption of endotoxins.