The potential for pharmaceuticals used for the treatment of disease in lactating cows causing violative milk residues that may pose a risk to human health is being scrutinized by regulatory authorities using tests that are more sensitive than conventional screening tests.

New milk residue screening testThe Cyclone Custom Analyte Detection Service (CYCADS) group at Iowa State University’s College of Veterinary Medicine now has available a new liquid chromatography–mass spectrometry (LC-MS) screening test that will provide dairy veterinarians with an assay similar to the one used by the Food and Drug Administration and other regulatory authorities.

There are some issues with current testing methods, says Hans Coetzee, BVSc, PhD, Cert CHP, Dipl. ACVCP. “Qualitative immunoassays used for routine drug screening are cost effective and provide rapid results, but these are generally non-specific tests for ‘inhibitory substances’ and not specific compounds. They often only detect the presence of these substances at certain levels in the milk as opposed to determining the actual concentrations that may be present.”

Coetzee says the methodologies used by pharmaceutical companies to determine drug tolerance concentrations in milk have not been available or economically feasible for producers to use. “Producers would benefit from having access to a highly sensitive and specific confirmatory test similar to the one used by regulatory authorities to determine actual drug concentrations in milk.”

The new test is available for a fraction of the cost normally associated with conducting this type of screening in other labs, Coetzee explains. “The CYCADS assay also includes several compounds that can legally be used in an extra-label manner by dairy veterinarians, most notably, to provide pain relief since there are no drugs are specifically approved for this purpose in the United States.”

 Uses for the test

The primary use for the test would be to identify and quantify drug concentrations in samples that are testing positive on conventional screening tests but that were derived from cattle that have no treatment history or that are outside the recommended milk withdrawal period for a product that was administered previously. This test can be used to determine drug depletion in milk after a drug has been administered in an extra-label manner. “This test would allow veterinarians to fulfill the requirements of AMDUCA after ELDU by ensuring that food for human consumption is free of drug residues,” Coetzee says.

This test could be used to analyze milk from recently purchased cattle prior to them joining the rest of the herd as part of a herd biosecurity protocol to ensure that milk is not contaminated, and it may be useful to determine if dairy feed has been adulterated with antimicrobials used in beef and swine production. This test may be useful to see if a herd is adhering to accepted drug treatment protocols and may thus form part of a total milk quality assurance program.

“Detection of drug concentrations below the regulatory threshold may highlight areas of drug use on the farm that need to be addressed before these become a regulatory concern,” Coetzee says. He is quick to point out that the goal of the CYCADS lab is not to provide withdrawal period recommendations. “That is the function of FARAD. Our role is to provide a third-party quality assured diagnostic service, and it’s up to the client to interpret the information.”

The cost of the test is $50/sample when a specific compound is screened for. If screening for all 39/41 compounds the cost is $75/sample. If analysis for aminoglycosides and chloramphenicol is needed, the cost is $150 but neither of these drug classes is approved for use in food animals. Turnaround time is two days.

“This new assay can dramatically decrease the time that milk from these cows need to be dumped because we can tell which drugs are present and if the drugs are below the safe concentration or tolerance,” Coetzee says.

Samples should contain at least 20 mL of milk, frozen and submitted on ice to the lab by overnight shipping. A downloadable sample submission form can be found at: