Systemic bioavailability of erythromycin in cattle when applied by footbath.
This study was conducted to determine the systemic bioavailability of erythromycin, a commonly used footbath antibiotic, after the treatment of 4 cows with digital dermatitis. The footbath was filled with 280 litres of water and added with 690 mg of erythromycin/litre of water where the feet of the cows were immersed for 2 min. 48 milk and 40 blood samples were collected and a microbial agar diffusion method was used to identify the erythromycin concentration using Micrococcus luteus. No erythromycin was detected in any of the 48 milk samples. Only 1 of the 40 plasma samples contained erythromycin collected 4 h after treatment on day 2. It is concluded that the bioavailabity of erythromycin after an antibiotic footbath is exceedingly low and providing footbathing is undertaken immediately after milking, unlikely to result in antibiotic contamination of milk.