title: Bacillus stearothermophilus disk assay detection of penicillin in milk of dairy cows after postestrual intrauterine infusion.
abstract: Penicillin concentrations were quantitated in milk from cows after intrauterine infusions of various amounts of penicillin. Six healthy lactating Holsteins were assigned to 3 treatment groups in a complete randomized block design. Postestrual (12 to 48 hours) intrauterine infusions of potassium penicillin G in sterile diluent were given at 1 of 3 dosage levels: 2 X 10(6) IU (group I), 1.5 X 10(6) IU (group II), or 1 X 10(6) IU (group III). Milk samples were collected from 0 to 72 hours after infusion and were frozen until assayed for detectable antibiotic residues by the Bacillus stearothermophilus plate disk test. Intrauterine infusion of 1, 1.5, or 2 million IU caused detectable penicillin residues (greater than or equal to 5 mIU/ml) within 12 hours after infusion in milk from 15 of 18 cows. After 12 hours, no samples were positive in groups II or III and only 3 of 30 samples representing 2 of 6 cows were positive in group I. Using the B stearothermophilus plate disk test, a cow given 1 to 2 million IU of potassium penicillin G intrauterine will have detectable amounts of antibiotics in the milk within 12 hours. It is unlikely that herd composite milk samples would contain detectable concentrations of antibiotics unless a large percentage of the herd was infused or unless massive doses were administered to individual cows.
mesh_terms: D000818:Animals; D002417:Cattle; D003470:Culture Media; D005260:Female; D001411:Geobacillus stearothermophilus / Q000187:drug effects; D008892:Milk / Q000032:analysis*; D010400:Penicillin G / Q000032:analysis* / Q000494:pharmacology
chemical_list: D003470:Culture Media; D010400:Penicillin G