Beta adrenergic agonists (p-agonists, repartitioning agents) have been studied in livestock species for more than two decades for their effects as lean efficiency enhancing agents. Work began at several pharmaceutical laboratories in the late 1970s. Patents were issued and initial reports were made in the mid-1980s.[1-3] More recently, data have been generated to meet registration requirements, define the physiological effects, and define parameters needed to optimize responses. Two compounds have regulatory approval to be used in livestock. Zilpaterol is approved for cattle in South Africa and Mexico (Intervet), and ractopamine is approved for use in swine in 21 countries including the United States and for use in cattle in the United States (Elanco Animal Health). Several reviews of p-agonist use in livestock have been published. Anderson et al. provide an extensive review with over 360 citations, Moloney et al. provide an especially complete summarization of efficacy for various compounds, and an updated review of mechanism of action is provided by Mersmann and Moody et al.
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