Animal & Veterinary
Drawing Residue Samples From Live Animals
by Richard L. Arkin
FDA Veterinarian Newsletter March/April 2005 Volume XX, No II
Studies involving tissue-fluid correlation in beef steers hold promise for new test methods that will be able to determine whether drug residues in beef steers are below tolerance levels while the animals are still alive, rather than after they have been slaughtered. These “on-the-hoof” test methodologies could mean less waste and lower production costs.
Scientists at the Center for Veterinary Medicine’s (CVM) Office of Research are using liquid chromatography tandem spectrometry (LC/MS/MS) methods to study the distribution of the drugs gentamicin and penicillin in the blood, urine, and kidney tissue of beef steers and relating their findings to the amount of drug residue in animal muscle. The theory is that drug levels in the physiological fluids can be related to drug levels in edible tissues. If so, producers, processors, and regulators could conduct tests on live animals before slaughter to determine if drug levels in edible tissues are violative. If so, the animals could remain alive for -longer periods to allow the drugs to clear to nonviolative levels.
If firm relationships between fluid drug levels and drug levels in edible tissues can be established, screening test kits could be developed that would provide a positive response to drug levels in the urine, saliva, or plasma that would correlate to a violative drug concentration in meat. This will allow a rapid decision whether to slaughter a drug-treated steer or keep it in the feeding pen for an additional period.
CVM scientists have developed laparoscopic techniques to periodically biopsy the kidneys of drug-treated steers. These techniques permit simultaneous monitoring of drug depletion in biological fluids and kidney tissue for the establishment of precise correlations. Methods based on LC/MS/MS have proven to be vital for the measurement of drug concentration in the small samples taken with the laparoscopic procedure: 100 milligrams or less. Kidney tissue samples are already used in new animal drug research. However, until now, kidney tissue samples have been obtained only from slaughtered animals. As a result, kidney tissue sampling has been limited to a single time point for each animal. In the slaughterhouse, reliance on testing organs such as kidney has meant that a complete animal carcass must be disposed of if the kidney tissues reveal violative drug residues.
In contrast, a laparoscopic procedure allows researchers to obtain tissue samples at various time points from the same animal. Successful laparoscopic techniques will reduce the total number of animals required for research and limit or perhaps eliminate the impact of biological variations between individual animals. The data from this research can be used to support live animal testing programs to reduce residue violations and the associated economic loss.
The Office of Research has provided the data and findings from these studies to the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS). The data will allow the development of on-site screening tests for live animals either for use by FSIS in regulatory testing or by producers and processors in HACCP (Hazard Analysis and Critical Control Point) quality systems. FSIS partially funded this research through an interagency agreement with CVM.