Posted April 16, 2015
A survey targeting dairies with histories of illegal drug residues in tissues of their cows at slaughter found that about 1 percent had illegal residues in milk.
None of the confirmed residues identified in milk from those dairies or from control dairies would have been found through routine testing of tankers of raw milk, according to a Food and Drug Administration report on the survey findings. But a related agency announcement states that, with violations found in less than 1 percent of all samples, the survey shows the milk supply is safe.
“These findings provide evidence that the nation’s milk safety system is effective in helping to prevent drug residues of concern in milk, even in those limited instances when medications are needed to maintain the health of dairy cattle,” an agency announcement states.
The routine tests conducted under the Pasteurized Milk Ordinance for Grade ‘A’ milk and milk products are intended to detect the presence of beta lactam drugs, the antimicrobials used most often on dairy farms.
||(Photo by Greg Cima)
In the survey, “None of the drugs found in the targeted or non-targeted groups are approved by FDA to be administered to lactating dairy cows,” the report states. “This means that FDA has not evaluated the use of these drugs in lactating dairy cattle, including whether milk from treated cows is safe for human consumption.”
The FDA plans to use the survey data in ranking risks and, “as necessary,” require tests for a more diverse group of drug classes in milk to participate in the Grade “A” milk program, the report states. The agency also plans to work with state regulators to add tests of milk in tanks on farms when investigating tissue residues in cattle sent to slaughter, as well as work to educate dairy farmers on practices to prevent residues.
The FDA conducted the tests on 1,900 milk samples to determine whether drug residues were more common in milk from farms that have sent to slaughter cows with tissues containing illegal residues. About half the samples came from dairies found to have tissue-related residue violations between 2007 and 2010, and the other half of samples came from a control group without prior violations. Eleven of the 15 samples found to contain illegal residues came from the farms with histories of violations.
The agency tested for 31 residues and identified violations on the basis of their presence at concentrations above tolerances or on the basis of detection at any level in the absence of established safe tolerance levels. The targeted group of dairies had such residues in 1.2 percent of samples, near triple the rate for dairies without prior violations.
Ten of the samples contained illegal residues of florfenicol, including all four of the samples from dairies without prior violations. The rest of the illegal residues were from ciprofloxacin, sulfamethazine, tilmicosin, tulathromycin, and gentamicin. Ciprofloxacin, a human-use drug, is a metabolite of the animal-use drug enrofloxacin.
Dr. M. Gatz Riddell, executive vice president of the American Association of Bovine Practitioners, said the survey results were encouraging because of the low numbers of residues found. But he said the results also show that work to prevent residues in meat and milk, like work to improve animal welfare, involves continuous improvement.
He said most of the illegal residues found by the FDA likely resulted from legal extralabel administration under veterinarian supervision.
Although veterinarians are prohibited from extralabel administration of enrofloxacin and sulfamethazine to lactating cattle, they can administer or recommend extralabel administration of florfenicol, gentamicin, tilmicosin, and tulathromycin.
Dr. Riddell said veterinarians need better information on how sickness and systemic compromise affect drug metabolism, which would help them develop withdrawal times sufficient to reduce any residues to levels lower than those detectable under current testing, which is already highly sensitive and is expected to become even more sensitive in the future. In the absence of withdrawal times that both avoid residues and allow a return to milk production, Dr. Riddell said veterinarians should consider alternatives to some antimicrobial treatments.