Carcass Characteristics and Quality Attributes of Beef from Cattle Supplemented Zinc and Ractopamine Hydrochloride

The objective of this experiment was to identify the impact of supranutritional zinc (SUPZN) and ractopamine hydrochloride (RAC) supplementation of beef steers on postmortem protein degradation and tenderness development of extended (>14 d) aged steaks. It was hypothesized that RAC and SUPZN supplementation would influence meat quality development during extended aging of the longissimus thoracis muscle. Crossbred steers (n=27) were fed in a 2 × 2 factorial: control (CON; analyzed 36 mg Zn/kg dry matter) or supranutritional Zn supplementation (SUPZN; CON diet + 60 mg Zn/kg dry matter [from ZnSO4] + 60 mg Zn/kg dry matter [from Zn–amino acid complex]) dietary treatments for the entire 91-d trial. Before harvest (30 d), steers were blocked by body weight within Zn treatments to RAC treatments of 0 or 300 mg per steer per day. Steers were harvested at a commercial processing facility. Carcass characteristics were collected 2 d postmortem. Warner-Bratzler shear force of the Longissimus thoracis was measured at 7, 14, 28, and 42 d postmortem. Calpain-1 autolysis (2 d postmortem) and desmin degradation (2, 7, 14, 28, and 42 d postmortem) were analyzed. RH resulted in greater (P<0.02) Warner-Bratzler shear force values at 7, 14, and 28 d postmortem, lesser (P<0.01) calpain-1 autolysis (76-kDa band) at 2 d postmortem, and lesser (P<0.02) desmin degradation at 2, 7, 14, and 28 d postmortem. Supplementation of Zn resulted in greater (P<0.01) calpain-1 autolysis (78- & 76-kDa band) at 2 d postmortem and a trend for greater (P=0.08) desmin degradation at 2 d postmortem. Tougher steaks from RH supplemented steers were explained by slowed postmortem proteolysis, and Zn supplementation showed evidence to enhance proteolysis early postmortem (2 d). These results demonstrate that nutritional supplementation can impact the rate of tenderness development and postmortem proteolysis in muscle.