Determining the Persistence of Xylazine and Ketamine in Cattle Tissue Following a Simulated Rendering Process.

Humane euthanasia is an endpoint for production animals succumbing to disease or trauma. Euthanasia performed with barbiturates or other anesthetic/sedative drugs observes zero withdrawal time, and drug residues may remain in tissues. Carcasses may be submitted for rendering, and rendered products can be used to manufacture pet foods. The purpose of this study was to determine the concentration of two drugs, xylazine and ketamine, that may be used during the euthanasia process of food animals and to determine the fate of these drugs following a simulated rendering process using a commercial autoclave. Twelve cattle were administered xylazine or xylazine and ketamine prior to euthanasia via penetrating captive bolt, and samples of muscle, fat, liver, and kidney were collected. The tissue samples were analyzed by LC-MS/MS, both raw and following rendering. The parent compounds xylazine and ketamine were detected in all tissues, both before and after rendering. The highest concentrations were found in rendered kidney for both drugs, and the lowest in rendered and raw fat for xylazine and ketamine, respectively.