Ractopamine withdrawal, depletion, and residue testing in beef cattle
Date
2019
Authors
Davis, Haley E., author
Belk, Keith E., advisor
Engle, Terry, committee member
Geornaras, Ifigenia, committee member
Prenni, Jessica, committee member
Yang, Hua, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Studies were conducted to evaluate use of ractopamine hydrochloride (RH) in beef cattle production and the effect of various withdrawal times and depletion periods on residues in tissues and fluids collected from live and harvested animals. Primary objectives of these studies were: i) to develop and validate a LC-MS/MS assay to determine if detectable and quantifiable levels of RH can be detected in digestive tract-derived edible offal items of cattle resulted from tissue residues or residual ingesta contamination; ii) to determine presence of ractopamine in tissues after 12 h, 2, 4, and 7 days of withdrawal (in comparison to negative control cattle which did not receive RH); iii) to develop U.S. beef industry best practices for RH use for export to the Chinese market; and iv) to test the impact of withdrawal from ractopamine hydrochloride in the diets of feedlot cattle for 2, 4, or 7 days on residues for parent and total ractopamine in muscle, fat, rendered tallow, and large intestines in contrast to a true negative control group as well as validate and test feed samples to verify ractopamine presence using LC-MS/MS protocols. In the first study, tissue samples and corresponding rinsates from 10 animals were analyzed for parent and total ractopamine (tissue samples only). The lower limit of quantitation was between 0.03 - 0.66 ppb depending on tissue type, and all tissue and rinsate samples tested had quantifiable concentrations of ractopamine. The greatest concentration of tissue specific ractopamine metabolism (represented by higher total vs. parent ractopamine levels) were observed in liver and small intestine. Contamination from residual ingesta (represented by detectable ractopamine in rinsate samples) only was detected in small intestine, with a measured mean concentration of 19.7 ppb (+/- 12.2 ppb). Taken together, these results underscored the importance of the production process and suggested that improvements may be needed to reduce likelihood of contamination from residual ractopamine in digestive tract-derived edible offal tissues for market. In the second study, liver and muscle samples were collected after 2, 4, and 7 days of withdrawal from RH due to regulatory issues surrounding 12-h samples. Parent and total ractopamine residues in individual liver samples ranged from a minimum of 3.40 and 3.46 ppb, respectively, for the control treatment group, to a maximum of 3.54 and 14.19 ppb, respectively, for the 2-day withdrawal treatment group. For the individual muscle samples, parent and total ractopamine concentrations ranged from below the limit of quantification (0.12 ppb) in the control samples, to 1.13 (parent ractopamine) and 1.72 ppb (total ractopamine) in 2-day withdrawal samples. Therefore, overall, parent and total ractopamine concentrations detected in the liver and muscle samples fell far below the MRL set by Codex and FDA. The greatest parent and total ractopamine levels (282.40 and 289.85 ppb, respectively) were detected after 12 h withdrawal in individual large intestine samples, followed by small intestine (142.26 and 181.91 ppb, respectively) and omasum (109.70 and 116.90 ppb, respectively) samples. Because detectable levels of ractopamine were identified in tissues collected from control animals (i.e., animals not receiving RH in their ration), further research was conducted to determine potential sources of ractopamine contamination, and frequency and accuracy of testing in global markets. For example, eight feed-grade tallow samples were analyzed for parent and total ractopamine presence as a potential source of contamination, especially in cattle not receiving ractopamine in their rations. Ractopamine concentrations of 0.40 to 50.80 ppb were obtained for these tallow samples. While this could potentially explain the detectable levels of ractopamine residues found in control samples and the fact that 7-day withdrawal did not result in non-detectable levels, further research looking at tallow recycling and residual proteins in tallow is necessary to understand the implications of contaminated tallow on residue levels across tissues. Data from the current study may be useful in developing new recommendations for RH use and withdrawal to beef cattle producers in the U.S. who intend to export to global markets. Results from the third study revealed several items of interest, for example; RH declines rapidly in the lower GI of beef cattle, with levels below detection by day four. Additionally, there is a very small likelihood of RH cross-contamination via tallow inclusion in diets. Finally, the fourth study indicated that RH residues can, in fact, be quite low; however, because of limits of detection which are above zero, it is nearly impossible to quantify a level as 0.00 ppb, making zero tolerance requirements insurmountable. Overall, results of these studies were promising in that they showed that RH levels were lower than once thought, but there is a long way to go before zero-tolerance requirements can be met.
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Subject
depletion
residue testing
beef cattle
withdrawal
ractopamine