Comparison of National Research Council standards and industry dietary trace mineral supplementation strategies for yearling feedlot steers12

A total of 360 steers (initial BW = 350 kg, SD = 28.1 kg) were used in a randomized complete-block-design experiment to determine the effects of trace mineral concentration and source on feedlot performance, carcass characteristics, liver trace mineral status, and diet in vitro solubility of Cu and Zn. Target treatments consisted of (1) basal diet; (2) basal diet supplemented with 10 mg of Cu from CuSO4, 30 mg of Zn from ZnSO4, 20 mg of Mn from MnSO4, 0.50 mg of I from ethylenediamine dihydriodide, 0.10 mg of Se from Na2O3Se, and 0.10 mg of Co from CoCO3 per kilogram of DM (NRC); (3) basal diet supplemented with the same sources of Cu, Zn, Mn, I, Se, and Co as treatment 2 but provided at 20, 100, 50, 0.50, 0.20, and 0.20 mg of mineral/kg of DM, respectively (CNI); and (4) basal diet supplemented with 66.6% inorganic and 33.4% organic Cu, Zn, and Mn and inorganic forms of Co, I, and Se at iso-concentrations to treatment 3 (CNO). No differences (P > 0.10) between treatments for feedlot performance; final liver Zn, Mn, Se, and Co concentrations; and carcass merit were observed. In vitro procedures were used to examine the solubility of Cu and Zn from the diets used for the feeding experiment. Dry matter disappearance was similar across treatments (P > 0.10). Percentage of Cu and Zn solubilized after simulated rumen and abomasal digestion was less (P < 0.05) for the basal diet compared with NRC, CNI, and CNO diets and NRC compared with CNI and CNO diets. Under the conditions of this experiment, it appears that basal dietary concentrations of trace mineral were adequate for growth and performance of finishing yearling feedlot steers.