Submitted to: American Chemical Society
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2016
Publication Date: 8/21/2016
Citation: Shelver, W.L., Marx, A.A., Mcgarvey, A.M., Smith, D.J. 2016. Detection of ractopamine in sheep urine after exposure to trace levels of dietary ractopamine [abstract]. 252nd American Chemical Society Annual Meeting. 08/21-25/2016. Philadelphia, PA. AGRO 235.
Interpretive Summary: .
Technical Abstract: Ractopamine is a feed additive approved in the US for swine, cattle, and turkey usage to increase growth rates and improve feed efficiencies. Although ractopamine is approved for use with a zero day withdrawal period, trace levels detected by countries in which ractopamine is banned can resulted in import rejection. Our goal was to determine levels of ractopamine exposure that will result in its detection using qualitative and quantitative assays. Ractopamine was fed to sheep at 0 (ZERO), 0.001 (LOW), 0.01 (MED), and 0.1 (HIGH) mg/kg of diet (n = 4 per level, 0.5 kg of feed/day) for seven consecutive days and urine was collected daily about ~16 hrs post exposure. The HIGH dose represents 2% of the normal dose fed to hogs. On-site lateral flow assays (LOD ~1 ng/mL) of urine tested positive for ractopamine in each treatment group: ZERO (7.4%), LOW (0%), MED (82%), and HIGH (86%). With use of half maximum absorbance values (OD450nm ~1.4, 4 trials), ELISA testing resulted 0%, 3.6%, 86%, and 93% positives for ZERO, LOW, MED, and HIGH, respectively. Parent ractopamine in urine was below the method LOQ (0.7 ng/mL) using LC-MS/MS in all samples. However, when total ractopamine (parent + hydrolyzed metabolites) was measured, LOW animals contained residues less than the LOQ for all samples with 7 out of 28 samples showed above LOD ( 0.22 ng/mL), MED animals had ractopamine levels of 1.08-9.13 ng/mL and HIGH animals excreted 4.85-32.82 ng/mL of total ractopamine. Ractopamine is rapidly eliminated; nevertheless urine from sheep exposed to as little as 5 µg/day (MED) of ractopamine had > 80% chance of having a positive ractopamine urine sample detected by the screening assays which was confirmed by LC-MS/MS.