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Eight crossbred steers (BW 719.0 ± 65.0 kg) with ruminal and duodenal cannulae were used to examine the effect of trace mineral (TM) source on digestibility; ruminal and duodenal solubility of Cu, Zn, and Mn; and in vitro release of Cu, Zn, and Mn from the solid fraction of ruminal digesta. Experiment 1 determined the effect of TM source on DM and NDF digestibility in steers fed a corn silage and steam-flaked corn-based diet. Treatments consisted of 10 mg Cu, 20 mg Mn, and 30 mg Zn/kg DM from either sulfate TM (STM) or hydroxy TM (HTM) sources. Following a 14-d adaptation period, total fecal output was collected for 5 d. Dry matter digestibility was not affected by treatment, but NDF digestibility tended (P < 0.09) to be greater in HTM vs. STM supplemented steers. In Exp. 2, steers were fed a diet without supplemental Cu, Zn, or Mn for 19 d. Steers were then administrated a pulse dose of STM or HTM (2× the National Research Council requirements for Cu, Mn, and Zn) via the rumen fistula. Ruminal and duodenal samples were obtained at 2-h intervals starting at −4 and ending at 24 h relative to dosing. Ruminal soluble Cu and Zn concentrations were affected by treatment, time, and treatment × time. Soluble concentrations and percent soluble Cu and Zn in ruminal digesta increased (P < 0.05) above 0-h values for 10 h following dosing with STM, but not HTM. Concentrations of Cu and Zn in ruminal solid digesta were also affected by treatment, time, and treatment × time. Steers dosed with STM had greater (P < 0.05) solid digesta Cu concentrations at 2 and 4 h but lesser (P < 0.05) concentrations from 6 to 20 h post-dosing than those receiving HTM. Ruminal solid digesta Zn concentrations were greater (P < 0.05) in HTM vs. STM-dosed steers from 6 through 24 h post-dosing. Distribution of Mn in ruminal digesta was affected by TM source, but to a lesser extent than Zn and Cu. Duodenal soluble TM concentrations were variable and not affected by treatment. Binding strength of TM to ruminal solid digesta was estimated at 0, 6, and 12 h post-dosing using dialysis against chelating agents. The percentage of Cu and Zn released from ruminal solid digesta by dialysis against Tris–EDTA was greater (P < 0.05) at 12 h post-dosing from steers receiving HTM vs. STM. Results indicate that Cu and Zn from HTM have low solubility in the rumen and appear to be less tightly bound to ruminal solid digesta than Cu and Zn from STM.

Four hundred crossbred steers were used in a randomized complete block design to investigate the effects of supplemental Zn source and concentration, and dietary Cr on performance and carcass characteristics of feedlot steers fed a steam-flaked corn-based finishing diet. Steers were blocked by initial BW within cattle source (3 sources) and randomly assigned within block to 1 of 5 treatments. Before the initiation of the experiment, trace mineral supplement sources were analyzed for Zn and Cr. Zinc and Cr concentrations of the Zn sources were used to balance all dietary treatments to obtain correct Zn and Cr experimental doses. Treatments were the addition of: 1) 90 mg Zn/kg DM from ZnSO4 and 0.25 mg Cr/kg DM from Cr propionate (90ZS+Cr); 2) 30 mg Zn/kg DM from Zn hydroxychloride and 0.25 mg Cr/kg DM from Cr propionate (30ZH+Cr); 3) 90 mg Zn/kg DM from Zn hydroxychloride and 0.25 mg Cr/kg DM from Cr propionate (90ZH+Cr); 4) 60 mg Zn/kg DM from ZnSO4 and 30 mg Zn/kg DM from Zn methionine (90ZSM); and 5) 90 mg Zn/kg DM from Zn hydroxychloride (90ZH). Steers were individually weighed on d-2 and on 2 consecutive days at the end of the experiment. Initial liver biopsies were obtained from all steers at processing. Equal numbers of pen replicates per treatment were slaughtered at a commercial abattoir on day 162, 176, and 211; individual carcass data and final liver samples were collected. Total finishing dietary Zn and Cr concentrations were 118.4, 58.2, 114.2, 123.0, and 108.2 mg Zn/kg DM and 0.740, 0.668, 0.763, 0.767, and 0.461 mg Cr/kg DM, for treatments 1 to 5, respectively. Data were analyzed statistically using preplanned single degree of freedom contrasts. Steers receiving 90ZH+Cr had greater final BW (P < 0.04) and ADG (P < 0.03) when compared with steers receiving 90ZH. Additionally, hot carcass weight was 8.5 kg greater (P < 0.03) for 90ZH+Cr compared with 90ZH supplemented steers. Steers receiving 90ZH+Cr had greater longissimus muscle area when compared with steers receiving 90ZSM. Dry matter intake, G:F, morbidity and mortality, and all other carcass measurements were similar across treatments. These data indicate that under the conditions of this experiment, Zn source and concentration had no impact on live performance, liver Zn and Cu concentrations, and carcass characteristics. Supplemental Cr in diets containing 90 mg of supplemental Zn/kg DM from ZH improved final BW, ADG, and hot carcass weights.

Feedlot diets are typically fortified with trace minerals because the basal diet contains inadequate concentrations of certain essential trace minerals or the basal diet may contain elevated concentrations of known trace mineral antagonists. Providing mineral sources that are more available to the animal may allow for lower supplemental inclusion rates to the diet. A total of 400 crossbred steers (initial BW 336 ± 9.6 kg) were used to investigate the effects of supplemental Zn, Cu, and Mn concentration and source on performance and carcass characteristics of feedlot steers fed a steam-flaked corn–based finishing diet for 145 or 159 d. The experimental design was a randomized complete block design. Steers were blocked by weight and randomly assigned within block to 1 of 5 treatments (8 pens per treatment; 10 steers per pen). Treatments consisted of (1) sulfate (90 mg of Zn/kg of DM from ZnSO4, 17.5 mg of Cu/kg of DM from CuSO4, 48 mg of Mn/kg of DM from MnSO4); (2) hydroxy trace minerals (HTM-1; 30 mg of Zn/kg of DM from Zn hydroxychloride, 10 mg of Cu/kg of DM from basic CuCl, 20 mg of Mn/kg of DM from Mn hydroxychloride); (3) HTM-2 (45 mg of Zn/kg of DM from Zn hydroxychloride, 12.5 mg of Cu/kg of DM from basic CuCl, 29.5 mg of Mn/kg of DM from Mn hydroxychloride); (4) HTM-3 (60 mg of Zn/kg of DM from Zn hydroxychloride, 15 mg of Cu/kg of DM from basic CuCl, 39 mg of Mn/kg of DM from Mn hydroxychloride); and (5) HTM-4 (90 mg of Zn/kg of DM from Zn hydroxychloride, 17.5 mg of Cu/kg of DM from basic CuCl, 48 mg of Mn/kg of DM from Mn hydroxychloride). Steers were individually weighed on d −1, 0, 55, and 112 and pen weighed on 2 consecutive days at the termination of the experiment. On d 112, 3 steers per pen were bled via jugular venipuncture. Equal numbers of pen replicates per treatment were transported to a commercial abattoir (d 145 and 159) and slaughtered, and individual carcass data and liver samples, from the same animals bled on d 112, were collected. Pen initial BW was used as a covariate in the statistical analysis, and significance was determined at P ≤ 0.05. No differences were observed for final BW (P ≥ 0.42). Overall ADG, DMI, and feed efficiency were similar across treatments. Hot carcass weight, DP, YG, longissimus muscle area, adjusted fat thickness, KPH, and marbling score were similar across treatments. Concentrations of Zn, Cu, and Mn in liver and blood samples were similar across treatments. These data indicate that under the conditions of this experiment, supplemental Zn, Cu, and Mn concentration and source had no effect on performance, mineral status, and carcass characteristics in feedlot steers.

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.

Excess nitrogen excretion is viewed as a worldwide environmental problem, and blood urea nitrogen (BUN; mg/dl) has been shown to be a predictor of nitrogen excretion in cattle. As a result, the objective of this study was to identify factors influencing BUN in a cohort of Angus cattle. Steers (n = 98) were born between February and June of 2016 and entered Colorado State University’s Feed Intake Unit (FIU) in May 2017 at an average age of 394.6 ± 21.0 d. While in the FIU, steers were fed a growing diet consisting primarily of corn silage and alfalfa hay. Animals were subjected to a 20 d warm-up period and a 54 d individual feed intake test period. Blood samples were collected on d 50 of the test. A generalized linear regression model was used to determine factors important in the determination of BUN concentrations of individual animals. Factors considered were sire, BUN assay date, age, initial test weight, birth weight, weaning weight, average daily gain, dry matter intake, residual feed intake, pulmonary arterial pressure, ultrasound ribeye area, ultrasound back fat, ultrasound percent intramuscular fat, and feedlot pen. Sire (P < 0.0005; partial r(2) = 0.47), BUN assay date (P < 0.00005; partial r(2) = 0.46) and age (P < 0.005; partial r(2) = 0.18) were all important sources of variation of BUN concentration levels. Sire and assay date explained the largest proportion of variability in BUN concentration as evidenced by their partial r(2) values. Sample process date and age are factors in which cattle producers would have little control in mitigating BUN concentrations, but that could be adjusted for with proper data recording. Differences amongst sires, however, indicate genetic differences may be exploited to reduce BUN concentrations.