Dye marked antibiotics for lactating cow mastitis therapy.

Dye markings of intramammary antibiotic infusions could give a dairy farmer immediate visual warning that milk contains antibiotic residue. Six dye and antibiotic preparations for lactating cows were studied for rates of dye and antibiotic milk-out. Albacillin containing 1 X 10(5) IU of penicillin plus 150 mg of novobiocin combined with 25, 125, or 250 mg of Food, Drug, and Cosmetic Blue No. 1 or No. 2 per infusion was used. Thirty cows with healthy udders producing 13.6 to 22.7 kg milk per day were treated in all quarters twice in 24 h (0500 and 1500 h). Milk samples from 14 posttreatment twice per day milkings (0500 and 1500 h) were tested for dye and antibiotic residue. Dye content was determined by a visual method and subvisually by an ion exchange resin method. No antibiotic residues were found by the cylinder plate method after the second to fourth posttreatment milkings. Antibiotic residue was detected up to the sixth milking by Delvotest-P. Depending on the dye type and its concentration, milk was visibly blue for one to four milkings. Subvisual quantities for dye were detectable by the ion exchange resin method for three to five milkings. The preparation showing the most promise for farm use contained 250 mg Blue No. 1 per infusion. Milk from cows treated with this preparation contained visually and subvisually detectable dye through three or four and five milkings, respectively. The dye persistence exceeded or coincided with the maximum antibiotic persistence in nearly all cows treated regardless of dye formulation or method of antibiotic detection.