Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2018
Publication Date: N/A
Interpretive Summary: .
Technical Abstract: Introduction: Zilpaterol is a feed additive used to increase weight gain, improve feed efficiency, and increase carcass leanness in cattle. An on-site analytical method is needed to determine zilpaterol exposure in animals to assist producer and trade groups in avoiding un-necessary animal or carcass condemnation. Purpose: To determine the lowest level of zilpaterol in a mixed feed that returns positive immunochromatographic screening (ICS) results in urine and edible tissues of exposed sheep. Methods: Sheep were fed trace levels of zilpaterol HCl (0.001, 0.01, and 0.1 mg/kg of feed, L, M, H doses) for 12 consecutive days in 4 trials; animals were killed on withdrawal day (WD) 0 (L0, M0, H0) or 3 (H3). Urine samples were collected and analyzed by ICS on feeding days 0, 2, 4, 6, 8, 10 and 12 (L0, M0, H0) and on WD 1, 2, and 3 for H3 animals. Tissues were harvested at slaughter, ground, either diluted with water or extracted with ethyl acetate, and evaluated by ICS. Results: Of 96 total control urine samples, 3 tests were false positives. Urine collected from sheep in the L group returned 25 – 75% positive ICS samples. After day 4, all M0, H0 and H3 urine tested positive during treatment. All urine from H3 sheep tested positive on WD 1, 50% on WD 2, and 25% on WD 3. All H0 kidney, liver, and lung tissue extracts tested positive while 50% of muscle extracts were positive. Aqueous dilution of H0 tissues returned75% and 50% positive for liver and kidney respectively and 0% for muscle and lung thus is a less sensitive method. Significance: Immunochromatographic assays can be performed on-site to determine zilpaterol exposure providing “real time” (10 min) answers. Positive tissue results were returned only in H sheep, a zilpaterol exposure level approximately 1.3% of labeled feed.