Mike Payne, D.V.M.
Mike Payne, D.V.M.

The new FDA report on drug residues in milk concludes that milk is safe, but if they found any drugs at all, how safe can it really be?

Today, after four years in the making, the Food and Drug Administration released the final report of its milk drug sampling assignment. The survey screened nearly 2,000 samples of farm milk for animal drugs residues using state-of-the-art technology that detects contamination in minuscule, parts-per-billion concentrations. Before jumping into the FDA’s results, however, the fascinating and complicated history of the project deserves some background and context.

Keeping livestock healthy is good for both the animal and a farmer’s economic bottom line. Sick animals don’t perform well and livestock medications and the associated labor to administer them, aren’t cheap. All this explains the regular visits by large animal veterinarians to manage the dairy’s herd-health program, conduct check-ups and schedule vaccinations. Dairy cows on commercial farms probably see veterinarians more often than our kids see doctors. Similarly, dairy nutritionists routinely develop feed rations that promote both good milk production and cow health. The standard dairy cow probably eats a more balanced diet than we do.

Contrary to popular belief, however, what these dairy nutritionists don’t include in the feed is antibiotics to increase production. Such drugs are inevitably excreted in the milk, rendering it unsalable for human consumption. Every milk tanker leaving the farm is tested for the most common types of antibiotics.

A typical 6,000-gallon tanker of unprocessed milk is worth in the neighborhood of $10,000. In the event of a contaminated load of milk, the farmer is on the hook for the entire value of that destroyed product. All of this translates into a powerful motivation to keep even trace levels of drugs out of farm’s bulk milk tank. It should come as no surprise that of the 3.2 million tanker loads that were tested in 2014, only 14 thousandths of one percent were found to contain drug residues. That milk of course was never allowed to enter the human food chain. Perhaps even more importantly, no drug residues were detected in milk actually sent to grocery stores in 2014, nor were any found in 2011, 2012 or 2013.

Even with excellent care, cows can and sometimes do become ill and need to be treated. Because of a farmer’s very real concerns about contaminated milk tankers, treated cows are removed from their milking string and put into the farm’s hospital pen where they can be monitored, finish their course of treatment and complete the appropriate drug withdrawal period. These withdrawal periods (intervals before the cow can be milked or slaughtered for beef) are established by the FDA, based on drug depletion data submitted by the pharmaceutical company bringing a new animal medication to market. The science going into such packages is highly regulated and scrutinized, using “best laboratory practices” that can drive the cost of a new animal drug application to more than $50 million.

In spite of these precautions, a small number of the three million dairy cows slaughtered each year are found to have drug residues in their tissues. A real estimate of the prevalence of such positive cows is difficult to glean from government data, but the rate can probably be measured in the hundredths of a percent of all slaughtered dairy cows. There are a variety of circumstances that may cause these infrequent violations, including mistakes in animal identification or medical records, prolonged withdrawal time in an individual sick animal or simply a farmer’s lack of understanding of how to use the medication.

All of which brings us finally to the recent release of the bulk milk sampling report. The FDA understandably was interested in knowing whether a farm associated with drug residues in slaughtered animals was also more likely to have drug residues in their milk. In short: Would management problems on the meat side predict management problems on the milk side? FDA originally intended to begin sampling in January of 2011 but delayed the process as it refined its protocol.

Ultimately the milk from 1,912 dairies was tested, roughly half from dairies that had experienced a recent finding of residues in slaughtered carcasses, and the other half coming from farms without that history. The milk was tested for 31 different medications using the most sensitive methodology available, an analysis which can measure contaminants down to the parts-per-billion (ppb) range. To put this in perspective, a ppb concentration is roughly the same order-of-magnitude dilution that is achieved by dissolving a sugar cube in an oil tanker.

The results? Out of 1,912 farms sampled, only 15 were found to have violative residues. In addition, there was no statistical difference between the numbers of milk residues found on target farms versus those found on the control farms. The FDA concluded: “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.”

A reasonable consumer might ask, however, while 15 positives out of nearly 2,000 farms seems pretty low, how does the presence of any positive milk allow the agency to conclude milk is still safe? The basis for FDA’s confidence in the safety of our milk stems from the multiple safeguards built into milk safety regulations. The concentration of the drug compounds measured in the sampling assignment were in that parts-per-billion range, levels that are inconsequential to human health.

Tolerance levels in meat and milk are established by FDA and based on animal studies designed to show no harm to humans exposed daily to those concentrations for an entire lifetime. Importantly, even those calculated safe levels are further divided by an additional safety factor of either 10 or 100. The last important thing to remember is that the sampling protocol used by the FDA in this project can be considered a worst case scenario, since milk on the farm has been neither diluted in 50,000 or 100,000 gallon creamery silos, nor has it been exposed to processing activities like pasteurization temperature, which can further reduce activity of some drugs.

All of the above helps explain FDA’s confidence in the safety of our milk supply, and observations that support this judgment. In previous FDA testing in finished dairy product for drugs most likely to cause an allergic reaction, it didn’t detect any. In the last 50 years, there have been no reports of serious reactions or death associated with residue levels of livestock antibiotics in food. This tells us that the system is working as designed and food doesn’t get much safer than milk.

Still there is always room for improvement. In fact the FDA, state regulators and the dairy industry have already committed to work together to improve an already excellent history of product safety and that’s good news for everyone, farmers, regulators and consumers alike.

To read the full milk drug residue sampling survey report and to obtain additional related information, visit FDA’s Drug Residues webpage.

Michael Payne is a veterinarian at the Western Institute for Food Safety and Security (WIFSS), a center within the University of California’s School of Veterinary Medicine. In addition to being a DVM, Dr. Payne holds a PhD in livestock pharmacology and food safety.