Effects of differing withdrawal times from ractopamine hydrochloride on residue concentrations of beef muscle, adipose tissue, rendered tallow, and large intestine.

Haley E Davis,Keith E Belk,Jessica E Prenni,Valerie Lindstrom,Terry E Engle,Robert J Delmore,Jacqueline M Chaparro,Ifigenia Geornaras,Mahesh N Nair,A M Abd El-Aty

doi:10.1371/journal.pone.0242673

Abstract

Ractopamine hydrochloride (RAC) is a beta-agonist approved by the U.S. Food and Drug Administration (FDA) as a medicated feed ingredient for cattle during the final days of finishing to improve feed efficiency and growth. Maximum residue limits and U.S. FDA residue tolerances for target tissues have defined management practices around RAC usage in the U.S. However, many countries have adopted zero tolerance policies and testing of off-target tissues, presenting a major challenge for international export. Therefore, the objective this study was to determine the necessary withdrawal time among cattle group-fed RAC to achieve residue concentrations below tolerance levels in muscle and off-target tissues. Specifically, both total and parent RAC residues were quantified in muscle, adipose tissue, rendered tallow, and large intestines from animals group-fed RAC and subjected to withdrawal 2, 4, or 7 days before harvest. Ractopamine (parent and total) residues were below the assay limit of detection (< 0.12 ng/g) in all muscle and adipose tissue samples from animals in control groups (no RAC). However, RAC residues were detectable, but below the limit of quantitation, in 40% of tallow and 17% of large intestine samples from control animals. As expected, mean RAC residue concentrations in muscle, adipose tissue, and large intestine samples decreased (P < 0.05) as the RAC withdrawal duration (days) was extended. Irrespective of RAC withdrawal duration, mean parent RAC residue concentrations in muscle, adipose tissue, and large intestine ranged from 0.33 to 0.76 ng/g, 0.16 to 0.26 ng/g, 3.97 to 7.44 ng/g, respectively and all tallow samples were > 0.14 ng/g (detectable but below the limit of quantitation). Results of this study provide a baseline for the development of management protocol recommendations associated with withdrawal following group-feeding of RAC to beef cattle in countries that allow RAC use and intend to export to global markets which may be subject to zero tolerance policies and off-target tissue testing.

Highlights

Beef cattle producers have relied on growth and production enhancing technologies for over 50 years to increase production and improve feed efficiency [1]
While steroidal implants have been historically used for growth promotion through increased average daily weight gain and improvements in feed efficiency, beta-adrenergic receptor agonists were approved in the early to mid-2000s as a class of orally active growth enhancement technologies for use in beef cattle intended for harvest [1]
Beta-agonists are routinely used in some countries as medicated feed ingredients during the last three to six weeks of cattle finishing for improved feed efficiency and growth promotion [1, 2]

Summary

Introduction

Beef cattle producers have relied on growth and production enhancing technologies for over 50 years to increase production and improve feed efficiency [1]. There are currently only two beta-agonists, ractopamine (RAC) and zilpaterol (ZIL), approved by the U.S Food and Drug Administration (FDA) for use in food animal species for increased weight gain, improved feed efficiency, and increased carcass leanness [7]. Both RAC and ZIL were subjected to the New Animal Drug Approval (NADA) process, which is a robust registration system ensuring the safety and effectiveness of the compounds. ZIL is not currently used in beef cattle in the United States for animal welfare concerns; at the current time RAC is still commonly used by U.S beef producers

Objectives

Methods

Results