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Milk residues from a veterinarian’s perspective

Julia M. Smith for Progressive Dairyman Published on 18 April 2016

What’s the big deal?
Out of more than 3 million bulk milk pickup samples (Grade A and B) tested per year, fewer than 500 are positive today. That means fewer than one in 6,000 positives. Twenty years ago, about 3,000 samples were positive.

Six times fewer samples are positive today. We are doing a great job keeping residues out of the milk supply, aren’t we?

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Every bulk tanker load is tested for four of six beta-lactam drugs including penicillin, ampicillin, amoxicillin, cloxacillin, cephapirin and ceftiofur. The most common drug residue detected is a beta-lactam. Sulfonomides, fluoroquinolone and tetracyclines account for fewer than 20 detections per year.

According to the August 2015 list of method/drug by status by drug family, there are a number of validated and non-validated tests available to test a range of drugs including not only beta-lactams but also aminoglycosides, amphenicols, clorsulon, fluoroquinolone, macrolides, novobiocin, spectinomycin, sulfonamides, tetracyclines and flunixin.

Flunixin can be detected as part of a relatively new multi-family validated drug test, Charm FLUSLBL, which detects beta-lactams or flunixin.

But what about other types of drugs we may not be testing for regularly, if at all?

Are we overlooking a problem?

In 2012, the FDA Center for Veterinary Medicine conducted a milk drug residue sampling survey. Samples were collected from bulk tanks on farms (953) that had had prior meat residue violations and from a random sample of farms (959). These milk samples were tested for 31 drug residues using very sensitive techniques.

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Fifteen samples were found positive: 11 from farms with prior meat residue violations and four from the other farms. The difference was not statistically significant. Misuse of drugs “under the radar” was not rampant.

However, the results were concerning for another reason. The FDA survey tested for 31 drug residues – those routinely tested for in milk as well as ciprofloxacin, sarafloxacin, doxycycline, 5-hydroxyflunixin, virginiamycin, tilmicosin, chloramphenicol, florfenicol, tulathromycin and tripellenamine.

These drugs were tested for using liquid chromatography, mass spectrometry/mass spectrometry (LC-MS/MS) – a very sensitive and specific analytical approach. All of the non-routine drugs have a tolerance/safe level of zero (except the flunixin metabolite, 5-hydroxyflunixin, which has a tolerance of two parts per billion).

The FDA survey found one residue each of sulfamethazine, gentamicin, ciprofloxacin and tilmicosin, two of tulathromycin and 10 residues of florfenicol, for a grand total of 16 residues in the 15 positive samples.

According to 21 CFR 530.41, the following drugs are prohibited from extra-label use: ciprofloxacin, enrofloxacin, sulfamethazine (and most sulfa drugs), chloramphenicol, clenbuterol, DES, dimetridazole, ipronidazole, nitroimidazoles, furazolidone, nitrofurazone, fluoroquinolones, glycopeptides, phenylbutazone (in adult female cattle) and cephalosporins (other than cephapirin).

Residues of prohibited drugs and those used in an extra-label manner had been found in the survey.

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No one wants a drug residue

The veterinary community responded with concern. Wayward bottles of gentamicin not dispensed by the veterinarian of record needed to be identified and removed from farms. Discussion focused on determining under what circumstances drugs would be prescribed for extra-label use.

Some parts of the country have seen increasing scrutiny of drug prescription practices by FDA inspectors. The FDA considers the following lapses to be evidence of inadequate farm management practices:

  • Failure to maintain a valid veterinarian-client-patient relationship
  • Inadequate treatment records
  • Failure to identify and withhold treated cows from slaughter
  • Not following labeled directions

To a dairy farmer, the terminology used by FDA is insulting. The FDA insists it is only doing its job.

Are you doing your job to prevent residues?

We all like to pat ourselves on the back. The dairy industry sent 3.1 million dairy animals to slaughter in 2012. Of these, 360 (0.01 percent) tested positive for drug residues. Dairy cattle represent 8 percent of beef animals, so this can’t be a big problem, right? Wrong. The kicker is that 90 percent of residues from inspector-generated tissue samples at slaughter came from dairy animals.

We know tissue residues and milk residues are not the same thing, but preventing meat and milk residues is our responsibility. The Wisconsin Veterinary Medical Association has rolled out a program called Food Armor to bring veterinarians and producers together to prevent drug residues.

The program follows a Hazards Analysis and Critical Control Points (HACCP) approach by identifying potential risks, providing information and helping create an action plan to implement safeguards and management practices. Veterinarians in many other states are being trained to implement Food Armor.

Working with your veterinarian to implement judicious use of antibiotics and to safeguard the food supply from drug residues will improve outcomes and reduce costs on the farm. Using drugs properly every time will protect our ability to use these tools.  PD

Julia M. Smith, DVM, Ph.D., is an extension associate professor at the University of Vermont Department of Animal and Veterinary Sciences. This article was based loosely on her presentation to the Dairy Practices Council in November 2015.

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