The Influence of Supranutritional Zinc and Ractopamine Hydrochloride Supplementation on Early Postmortem pH Decline and Meat Quality Development of Beef

The objectives of this experiment were to determine the impact of zinc (Zn) and ractopamine hydrochloride (RH) supplementation of beef steers on early postmortem pH decline and meat quality development of aged longissimus thoracis steaks. Angus steers (n = 20; 516 kg average initial body weight) were fed in a 2 × 2 factorial and equally assigned to Zn and RH treatments: control (analyzed 36 mg Zn/kg dry matter [DM]) or supranutritional Zn supplementation (control diet + 60 mg Zn/kg DM [from ZnSO4] þ 60 mg Zn/kg DM [from Zn–amino acid complex]) dietary treatments for the entire 89-d trial. Starting 28 d before harvest, steers were blocked by body weight within Zn treatments to RH treatments of 0 or 300 mg per steer per day. Steers were harvested, and the following data were collected: longissimus thoracis pH and temperature (1, 3, 6, and 24 h postmortem), carcass measurements, and quality attributes of aged steaks (1, 3, 7, or 14 d postmortem). Muscle samples were taken at 1 h and 1, 3, 7, and 14 d postmortem for biochemical analysis. Supplementation of supranutritional Zn trended for a lower (pH 5.49; P = 0.06) pH in samples at 6 h postmortem and lower (5.40 kg; P = 0.06) Warner-Bratzler shear force value at 1 d postmortem. Supplementation of RH in samples resulted in a higher (pH 5.86; P = 0.04) pH at 6 h postmortem, greater (7.64 kg; P < 0.01) Warner-Bratzler shear force value at 1 d postmortem, and lesser whole muscle desmin (P = 0.05) and troponin-T (P = 0.04) degradation at 1 d postmortem. The observed differences in this study lends further credence to the need to more fully understand the role of Zn and RH in muscle growth and early postmortem metabolism because of potential impacts on beef quality.