A pilot program to begin screening every 15th tanker load of milk for tetracycline residues, scheduled to start in the second quarter of 2017, will likely be delayed.

The Food and Drug Administration (FDA) has yet to approve a second rapid-screen test kit for tetracycline, and without such a test, the program cannot begin, says Pat Gorden, an Iowa State veterinarian who follows the issue for both the American Association of Bovine Practitioners and the American Veterinary Medical Association.

Though a pilot program, the National Conference on Interstate Milk Shipments (NCIMS) is hopeful all states will participate. But implementation will be based on regulations within each state. FDA is obviously hoping a good number of processors will start screening tankers to see if tetracycline residues are an issue—or not.

Currently, processors screen every tanker load for beta-lactams. In 2015, just 317 tankers out of more than 3 million loads tested positive. That’s a violation rate of just 0.012 percent, which was down from 0.014 percent in 2014. (Results from 2016 have not yet been released.)

With that extremely low level of violation, FDA has wondered aloud if resources would be better spent looking for residues from other antibiotics. In April 2015, FDA released a risk assessment of 54 antibiotics, and ranked them according to which posed the greatest risk to human health. It came up with eight drug families, including beta-lactams. Others on the list include anti-parasitics including avermectin, macrolides, aminoglycosides, nonsteroidal anti-inflammatories, sulfonamides, phenicols and tetracyclines.

At the NCMIS meeting that convened shortly after the list was released, FDA and state health and dairy departments agreed to launch the pilot program. The tetracycline class of drugs was picked for screening because it was felt a screening test could be quickly developed. Tetracycline is commonly used to treat uterine infections (where it can quickly migrate to the udder) and in treating hoof lesions through topical applications and in foot baths.

There are a number of issues yet to be resolved. First, some of the rapid screening tests are set to detect residues as low as 100 ppb in bulk milk. The FDA tolerance level for tetracycline, however, is 300 ppb. So if a tanker initially tests positive at 100 ppb, a further dilution test will have to be done to determine if the milk is violative.

Second, that delay in testing may create a problem for the processor. No processor will want to unload the tanker into its milk supply until it clears, even though the 100 ppb residue is non-violative. And if it does clear at the 300 ppb level, what customer downstream will want milk that has some level of residue, albeit non-violative?

The chance of a violation is low. No tetracycline residues were detected in the 2012 screening of nearly 2,000 dairy farms that were tested for 31 drugs other than beta-lactams. In addition, a few, but large, dairy processing plants in California and the Northeast have already been screening for tetracycline and sulfas to meet international testing specifications. Less than a handful of those loads have been positive out of roughly 300,000 tankers tested over two years.

Still, in states that don’t mandate participating in the pilot program, some plants might decline to participate simply because they don’t want to deal with the issue or bear its costs—even if the risks are minimal.

You can read more on the issue here and here and here.