Residues Becoming More Elusive

While antibiotic or other drug residues in meat or milk remain a concern for some consumers, surveillance and survey studies from the FDA and USDA show the industry has made considerable progress.


The latest report, from USDA’s Agricultural Research Service (ARS), regards pork in Midwestern retail cases. In this survey, the ARS researchers purchased over 1,000 pork kidneys from four different retailers. Residues, if present, tend to concentrate in the kidneys, making them a logical tissue to sample.


In the initial testing, six of 1,040 samples, or 0.58 % tested positive when screened for antibiotics. The researchers then screened a 278-sample subset of the pork kidney samples with a more specific ELISA test for residues of four veterinary drugs:

  • Flunixin, a non-steroidal anti-inflammatory agent.
  • Ractopamine, an agent that enhances leanness in meat
  • Sulfamethazine, a class of antibiotics.
  • Tetracycline, a class of antibiotics.

The researchers note that the Enzyme-Linked Immunosorbent Assays (ELISAs) can measure residues at far lower concentrations than those called for by regulatory tolerances. In this testing, regardless of method, residue levels of all veterinary compounds were always well below U.S. regulatory tolerances. For example, of the samples assessed by the highly sensitive ELISA and other methods, only 4 % were positive for minute amounts of sulfamethazine, 10 % for trace quantities of tetracycline, and 22 % positive for detectable quantities of the commonly used feed additive ractopamine. The study results are published in the journal Food Additives & Contaminants.


Other studies in recent years have found very low incidence of violative residues in beef and in milk.


The record is not perfect of course, and the industry must continue to focus on judicious use of antibiotics and other drugs, comply with all label requirements for use and always observe withdraw times.


Also, as advancements in analytic technology continue, the threshold for measurable residues becomes increasingly lower. As long as the industry uses antibiotics or other animal-health products, residues will be detectable at some level. We can work to educate consumers about the sensitivity of testing and the difference between detectable and unsafe residue concentrations, but we also can expect their preferences to continuously move the bar toward lower and lower acceptable thresholds.


Access the report in Food Additives and Contaminants.


For more on recent research into antibiotic use and residues, see these articles on BovineVetOnline:

Tetracycline Pilot Project Finds Six Positives in 2018 Fiscal Year

OIE Report Shows Global Progress on Use of Antibiotics in Animals

Antibiotic Stewardship: FDA Cites Progress