In this study, 20 young steers received no beta-adrenergic agonist (C), 100 animals all received zilpaterol hydrochloride, with 1 group only receiving zilpaterol (Z) while the other 4 groups received zilpaterol and vitamin D3 at the following levels and durations before slaughter: 7 million IU Vit D3 /animal/day for 3 days (3D7M); 7 million IU Vit D3/animal/day for 6 days (6D7M); 7 million IU Vit D3/animal/day for six days with 7 days no supplementation (6D7M7N) and 1 million IU Vit D3/animal/day for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and the right side not electrically stimulated (NES). Samples were aged for 3 or 14 days post mortem. Parameters included Warner Bratzler shear force (WBSF), myofibril filament length (MFL), sarcomere length and calpastatin and calpain enzyme activities. For drip loss and instrumental colour measurements, samples were analysed fresh (1 day post mortem) or vacuum-aged for 14 days post mortem. Both ES-treatment and prolonged aging reduced WBSF (P < 0.001). Treatments 6D7M, 6D7M7N and Z remained significantly tougher than C (P < 0.001), while 3D7M and 9D1M improved WBSF under NES conditions. ES was shown to be more effective at alleviating beta-adrenergic agonist induced toughness than high vitamin D3 supplementation. Aging increased drip loss, lightness, redness and yellowness while ES increased drip loss. In general, Z showed increased drip loss, lighter meat, and reduced redness. Vitamin D3 supplementation could not consistently overcome the adverse effects of zilpaterol hydrochloride in feedlot steers.