Effects of Ractopamine Hydrochloride on Slice Shear Force within USDA Quality Grade of Feedlot Holstein Steers

The addition of β-agonists, such as ractopamine hydrochloride (RH), increase carcass weight and leanness when fed to Holstein steers. The objective of this experiment was to determine the effects of RH (Actogain, Zoetis) on Slice Shear Force (SSF) tenderness within USDA Quality Grade in Holstein steers. Holstein steers (n = 417; initial BW = 442 + 33.1 kg) were used in a randomized complete block design where RH was fed for 3 durations (28, 35, or 42 d) at 3 doses (0, 300, or 400 mg·steer-1·d-1). After harvest, SSF was measured on two 3.8 cm thick steaks selected from each side and aged either 14 or 21 d postmortem. Steaks were assigned a USDA Quality Grade based on marbling score (799 to 600 = High Choice; 599 to 401 = Low Choice; and < 400 = Select), and within USDA Quality Grade steaks were categorized into 3 tenderness categories (< 15.3 kg = very tender; 15.4 to 19.9 = tender; > 20.0 kg = tough) based on SSF value. With increasing RH dose, there was a linear increase (P < 0.001) in ADG. In addition, steers fed increasing RH had heavier HCW (linear effect, P = 0.02) and greater (linear effect, P = 0.01) LM area. Within USDA High Choice and Low Choice carcasses, after 14-d aging there was a linear decrease (P < 0.03) in very tender steaks and a linear increase (P < 0.05) in tough steaks as RH increased. For USDA Select carcasses there was a tendency (P = 0.06) for a linear increase in the percentage of tender steaks as RH increased. Duration of feeding resulted in a quadratic response (P = 0.04) for tender steaks from carcasses in the USDA High Choice Quality Grade, with steers fed for 35 d having the lowest percentage of tender steaks. After 21-d aging, there was no effect (P > 0.12) of dose of RH on tenderness within USDA Quality Grade. While the addition of RH to the diet of Holstein steers improved HCW and LM area, RH decreased the percentage of very tender steaks at 14-d postmortem. However, after 21-d aging, dose of RH did not affect tenderness within USDA Quality Grade category. Overall, the addition of RH to the diet of Holstein steers increased BW gain, HCW, LM area, and carcass leanness. Negative effects of RH on tenderness can be mitigated by aging steaks for 21 d.