Effects of Copper and Zinc Source on Performance, Carcass Characteristics, and Lipid Metabolism in Finishing Steers 1 2 3: 1

An experiment was conducted to determine the effects of Cu and Zn source on performance, trace mineral status, lipid metabolism, and carcass quality of finishing steers. In the study, 195 steers were blocked by origin, stratified by BW, and sorted into 24 pens. Pens within blocks were then randomly assigned to treatments in a 2 × 2 factorial arrangement. Factors were 10mg of Cu/kg of dietary DM from CuSO4 or 10mg of Cu/kg of dietary DM from organic Cu and 90mg of Zn/kg of dietary DM from ZnSO4 or 36mg of Zn/kg of dietary DM from organic Zn with 54mg of Zn/kg of DM from ZnSO4. Steers were fed a high concentrate finishing diet until they reached an approximate BW of 580kg. Diets were fed once daily in the morning to allow ad libitum access to feed throughout the day. Daily feed offerings were recorded and feed refusal was measured every 28 d. Body weights were recorded for each steer and blood samples were collected from 3 steers per pen every 28 d. Three weeks prior to slaughter, subcutaneous adipose tissue biopsies were taken from 1 steer per pen. Postharvest longissimus dorsi muscle samples were collected and evaluated for fatty acid composition. There were no Cu or Zn main effects or Cu × Zn interactions for ADG, DMI, or feed efficiency. The effect of Cu or Zn source was similar across treatments for hot carcass weight, dressing percent, rib eye area, subcutaneous fat thickness, kidney, pelvic, and heart fat, and marbling score. There was a Zn effect for calculated yield grade. Steers receiving organic Zn had a lesser (P = 0.03) calculated yield grade than steers receiving inorganic Zn. Serum cholesterol, plasma Cu and Zn concentrations, fatty acid composition of longissimus muscle and subcutaneous fatty acid synthase activity were similar across treatments. Results from this study indicate that trace mineral source had little influence on performance, carcass characteristics, and lipid metabolism.