METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Depletion of zilpaterol hydrochloride residues from the urine of orally treated horses
Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 24, 2008
Publication Date: August 17, 2008
Citation: Smith, D.J., Hammer, C.J., Mostrom, M.S., Thorson, J.F., Shelver, W.L. 2008. Depletion of Zilpaterol Hydrochloride Residues from the Urine of Orally Treated Horses [Abstract]. In: Program of 236th American Chemical Society National Meeting, Agrochemicals Division, August 17-21, 2008, Philadelph, PA. Vol. 75, Abstract #27, Page 76.
Zilpaterol HCl is a beta-agonist feed additive that was approved for use to increase body weight gain and improve carcass composition in feedlot cattle. Because zilpaterol is a non-steroidal production enhancer, it has the potential to be used illicitly as a doping agent in species used for competitive racing. The purpose of this study was to determine the depuration of zilpaterol after oral administration to horses. Two mares and a gelding were provided an initial dose of 0.17 mg/kg bw of zilpaterol in a corn-based feed supplement; a second dose of 0.022 to 0.043 mg/kg bw was provided 24 h after the initial dose. Urine was collected approximately 6 h after dosing and at 24 h intervals thereafter for 18 days. Mean urinary concentrations of zilpaterol, measured by indirect competitive ELISA after dilutions of 1:2 to 1:20,000, peaked at 1056 ± 549 ng/mL on day 2 of the study and remained detectable through day 18 of the study with mean concentrations of 1.3 ± 0.8 ng/mL (IC50, 0.24 ng/mL). These results suggest that a zilpaterol immunoassay may be useful for determining animals exposed to zilpaterol after prolonged depuration periods.