Zinc is a trace mineral of interest for optimizing growth in feedlot cattle due to its roles many physiological functions, including growth. Twenty-four Angus-cross steers (467 ± 13 kg) were used assess the effects supplemental Zn and ractopamine hydrochloride (RAC) on concentrations muscle gene expression. Four GrowSafe-equipped pens randomly assigned treatments (1 pen six steers/treatment): 0...