Animal Drug Residues... Where do they reside?

Julie L Brunkhorst, Heather L Henderson, Carrie Maune, and Ronald Niemeijer

Trilogy Analytical Laboratory, Washington, MO 63090




Concerns with Animal Drug Residues have increased over the past several years. The FDA recently released the Veterinary Feed Directive (VFD) "to promote the judicious use of antimicrobials in food-producing animals." Veterinary drugs are utilized by producers for disease treatment, heard health management, growth promotion, and meat quality management. Several drug residues can remain in the animal and as a result enter into the food chain. A limited study was performed to determine where the drug residues were located and at what concentrations. Samples of urine, blood, muscle tissue, liver and fat from each animal were obtained and tested by LCMSMS. Samples were prepared and analyzed using a modified FSIS method. Data obtained contained 29 different antibiotics and growth promoters.


Because of the recent emphasis on "antibiotic-free" meat, this investigation was performed. All of the beef cattle samples that were collected were considered to be antibiotic free. This study was performed for a few reasons:

To see if any antibiotics were present
If any were present, where they were most concentrated
If they would appear in all of the different samples collected
Would there be any correlation


Samples of urine, blood, muscle tissue, fat and liver from each animal were collected.

All samples were analyzed by a modified FSIS LCMSMS method.
Samples were ground if necessary
Weighed and extracted with 80/20 Acetonitrile/water
They were then purified with C18


Procedure continued

Defatted with Hexane
The Acetonitrile layer was then evaporated
Then reconstituted with 14/86 Acetonitrile/0.1% Formic Acid

Animal Drug Residues Image 1.png


The following shows the percent of each antibiotic found in the various types of samples:

Animal Drug Residues Image 2.png

Animal Drug Residues Image 3.png

* Results in red are above reported maximum residue limit.



Antibiotics were present in low levels in urine, muscle tissue, liver and fat in cows that were presented as "antibiotic free." Analytical results for most compounds were below maximum residue levels, however samples were found in urine, liver and fat samples above the MRL's. This study was limited as samples were collected from only one basic geographic area. This study does indicate antibiotic ingestion from some source in these animals. Tissue determinations indicated the smallest number of positive results for the antibiotics tested. Possible additional study protocols would include both a larger geographical region and increased number of overall animals tested. Additionally for future studies inclusion of the kidneys, liver, and feces for each animal may also provide additional insight into the distribution of the ingested residues.



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