Persistence of Antibiotics in Milk from Cows Treated Late in the Dry Period

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Abstract
Cows (19) were treated via intramammary infusion at various times prior to calving with 1 of 2 dry cow antibiotic preparations (cloxacillin or penicillin). Milk samples from these cows after calving were analyzed for antibiotic residues by the Sarcina lutea cylinder plate method. Cows (8) were treated with cloxacillin. Cloxacillin was detected in the milk of only 2 cows after calving and then for only 1 milking, so no problem should exist with cloxacillin if the manufacturer''s recommendations are followed. Penicillin residues were not detected in milk samples taken from cows treated more than 9 days prior to calving with the dry cow penicillin preparation; 7 of 9 cows treated with penicillin up to 9 days prior to calving had detectable penicillin residues in the milk from treated quarters after calving. Only 1 cow had detectable penicillin residues longer than the manufacturer''s recommended milk withholding time of 96 h, and this cow was treated only 3 days prior to parturition. Normal routine on a dairy farm and adherence to manufacturer''s recommendations should result in no antibiotic residue problems in milk from cows treated during the dry period for mastitis control with either cloxacillin or penicillin.