Quantitative Evaluation of a Bovine Antibiotic Infusion Product by Milk Residue Depletion Studies

Cows (six) were treated as for bovine mastitis by an intra-mammary infusion containing penicillin G, streptomycin, neomycin and polymyxin B sulfate. After termination of treatment, milk samples were drawn at intervals of 12 h and assayed for the antibiotics by standard techniques. Residues of penicillin, streptomycin and neomycin were found to persist beyond the milk withholding time of 96 h as stated on the label of the product. Streptomycin residue was found to persist in milk from 50% of the cows beyond 14.5 d, whereas no detectable level of polymyxin B was found in the milk samples. Manufacture of the formulation evaluated in this study was discontinued in 1983.