author(s)
Vikas V Karande, Ramesh Jagtap, DJ Kalita and BC Ghumare

abstract
The present study aimed to evaluate the persistence of strepto-penicillins in lactating Holstein Frisian cow milk followed by an intramuscular injection of strepto-penicillins consecutively for three days at 24 hrs interval. The collection of milk samples was performed twice daily up to the 10th milking followed by strepto-penicillins injection and milk samples were analysed by MS/MS. The detection limit of the method was determined as 0.1 μg/kg. The residues of the penicillin were not observed in the any of the milking. The highest concentrations of streptomycin were determined in the milking at 24Hrs after injection last injection and mean concentration of this milking was found to be as 1008.17µg/L, however at 72 hrs it was 151.5µg/L. streptomycin residue in all milk samples after 72 hrs of last administration was lower than the maximum residue limit (200 μg/kg). In conclusion, this study determined the persistence of streptomycin in cow milks based on an MS/MS method. In addition, results of the study showed that cow milk after intramuscular administration of strepto-penicillins showed withdrawal period of 72 hrs.