New research from the University of Minnesota and the University of Guelph in Canada suggests antibiotic treatments of hoof lesions can trigger milk residues.
As the U.S. Food and Drug Administration ramps up antibiotic testing for drugs other than beta lactams in the coming year or so, those residues could show up in screening tests.
Researchers sampled 50 cows in two herds that were in five hoof lesion treatment groups. Tetracycline was applied as either a wrap or paste, and then milk was sampled at various times after treatment.
In all, 442 milk samples were tested. Of that number, 105 samples of detectable tetracycline were found, with 35 having quantifiable results, says Gerard Cramer, a U of M veterinarian involved with the study. Five of the samples had residues above 100 parts per billion (ppb), testing in the range of 120 to 244 ppb.
In the United States, the maximum residue limit for tetracycline is 300 ppb; in the European Union, it is 100 ppb. So the milk samples with the higher residues would still be legal in the United States, but might not be eligible for export to the E.U.
It’s unknown whether the tretracycline was being absorbed by the lesions and then transported to the udder, or whether teats were simply being contaminated when cows laid down and teats came in contact with the hoof.
In any case, the research shows that tetracycline residues are possible. It’s important hoof trimmers and veterinarians applying the tetracycline pay very attention to dosages, says Cramer. “Two to three grams per lesion is adequate,” he says. “That’s important to keep in mind because treatment is not risk free.”