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Competing Interests: The authors declare that they have no conflicts of interest relevant to the content of this article.

Chelated copper ( Cu ) sources, such as Cu glycinate ( CuGly ), may be more bioavailable relative to Cu sulfate ( CuSO 4 ) when fed to ruminants under antagonistic pressure. The objective of this study was to determine the bioavailability of CuGly (GemStone Cu; Phibro Animal Health) relative to CuSO 4 in steers fed a diet supplemented with 0.3% sulfur and 2 mg molybdenum/kg of dry matter ( DM ). Sixty Angus crossbred steers ( n  = 12 per treatment) averaging 288 ± 4.85 kg were enrolled in a 90-d study and fed a corn silage-based diet with one of five Cu supplementation strategies, including no supplemental Cu (CON ), 5 or 10 mg supplemental Cu from CuSO 4 /kg DM, and 5 or 10 mg supplemental Cu from CuGly/kg DM. Steers were housed in pens equipped with GrowSafe feed bunks (GrowSafe Systems Ltd., Airdire, AB, Canada), with six steers per pen. Growth performance, liver Cu, and plasma Cu were analyzed in the MIXED procedure of SAS 9.4 (SAS Inst. Inc, Cary, NC) with orthogonal contrasts to compare CON vs. 5 mg Cu/kg DM, CON vs. 10 mg Cu/kg DM, 5 vs. 10 mg Cu/kg DM, and CuSO 4 vs. CuGly. Copper indices were regressed against Cu intake and slopes were calculated using the GLM procedure SAS. Dietary Cu supplementation did not affect steer body weights on days 0, 28, 56, or 90 ( P  ≥ 0.52), average daily gain, dry matter intake, or gain:feed ( P  ≥ 0.36). Final plasma Cu concentration did not differ between CON vs. 5 mg Cu/kg DM ( P  = 0.79), CON vs. 10 mg Cu/kg DM ( P  = 0.65), or 5 vs. 10 mg Cu/kg DM ( P  = 0.39). Steers receiving CuSO 4 tended to have greater final plasma Cu concentrations than those receiving CuGly ( P  = 0.08). Initial liver Cu concentration averaged 374 mg Cu/kg DM, which is considered highly adequate. No steers reached deficient Cu status by the end of the 90-d period. Control steers had lesser final liver Cu concentrations than supplemented steers ( P  ≤ 0.04). Steers receiving 10 mg supplemental Cu/kg DM had greater liver Cu concentrations than those receiving 5 mg supplemental Cu/kg DM ( P  = 0.01). Copper source had no effect on final liver Cu concentrations ( P  = 0.57) and based on liver Cu and Cu intake the bioavailability of CuGly was similar to CuSO 4 (115%; P  = 0.27). The initially high Cu status and the fact that cattle did not become Cu deficient may have impacted the relative bioavailability results, and more research is needed to investigate the role initial Cu status and antagonistic pressure play in the bioavailability of chelated Cu sources., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The study's aim was to evaluate the effect of dietary Zn supplementation on steer performance, biomarkers of inflammation and metabolism, and liver abscess formation in response to a mild acidosis challenge. Forty-two steers (417 ± 3.99 kg; n = 6/pen) were housed in pens with bunks designed to measure individual dry matter intake ( DMI ) and fed one of two diets containing either 0 (CON; n = 18) or 90 mg Zn/kg from a Zn-amino acid complex ( Zn-AA ; n = 18; AvailaZn; Zinpro) for 109 d. Six additional steers were fed the CON diet and did not undergo the acidosis challenge ( NON ; n = 6). The acidosis challenge included restricting steers to 50% of the previous 7 d daily DMI on days 46 and 47, steers were individually provided 10% of DMI as cracked corn (as-fed) at 0800 h followed by ad libitum feed access 2 h post-grain consumption. Steer was the experimental unit, and two contrasts were constructed: NON vs. CON and CON vs. Zn-AA. Blood samples were collected on days 40, 48, 53, 69, 80, and 108 and analyzed as repeated measures. Final body weight and overall average daily gain (2.29, 2.30, and 2.31 ± 0.920 kg/d for CON, Zn-AA, and NON, respectively) were not different ( P ≥ 0.74) between treatments. By design, DMI was greater ( P < 0.01) for NON compared to CON on day 46 but was not different ( P ≥ 0.41) for the rest of the experiment. While hot carcass weight (423, 428, and 424 ± 7.9 kg for CON, Zn-AA, and NON, respectively) and ribeye area were not different ( P ≥ 0.53) due to treatment, marbling score tended ( P = 0.06) to be greater in CON compared to Zn-AA. The 12th rib backfat thickness was greater ( P = 0.05) in NON vs. CON steers. Liver abscess incidence tended to be greater ( P = 0.12) in CON (24% abscesses) vs. Zn-AA (6% abscesses). NON had a greater incidence ( P = 0.05; 50% abscesses) compared to CON. Overall, blood fibrinogen and leukocyte counts were not different between treatments ( P ≥ 0.67); however, neutrophil-to-lymphocyte ratio tended to be greater in NON vs. CON ( P = 0.08). Serum aspartate aminotransferase and gamma-glutamyl transferase concentrations were greater in NON vs. CON ( P ≤ 0.02), and serum alkaline phosphatase concentration was lesser in CON vs. Zn-AA ( P < 0.01). Overall, dietary Zn supplementation tended to lessen incidence of liver abscesses with limited impacts on overall cattle performance. Shifts in liver enzymes may represent opportunities to identify cattle with liver abscesses earlier in the feeding period., Competing Interests: Lundy-Woolfolk, Genther-Schroeder, and Hansen declare no conflicts of interest. Branine is an employee of Zinpro Corp. and reviewed the manuscript but offered only grammatical suggestions for improvement. The content was at the discretion of the Iowa State University researchers., (© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The objectives were to assess the effects of dietary Sweet Bran (Cargill Corn Milling, Blair, NE) on performance and feeding behavior of feedlot steers and determine if terminal implant pen sorting affects performance, feeding behavior, and liver abscess (LA) rate. Two hundred sixteen Angus-cross steers (253 ± 18 kg) were stratified by body weight (BW) to 36 pens. From d 0 to 60, diets contained 40% Sweet Bran (SWBR) or 25% modified distiller's grains and 15% dry rolled corn (MOD; n = 18 pens/treatment). On d 60, steers began transition within treatments to finishing diets containing 25% Sweet Bran or 25% modified distiller's grains (MDGS). On d 111, half of the pens for each dietary treatment were re-stratified by BW to pens (SORT) while the other half were returned to original pens (NOSORT; n = 9 pens/treatment). Steer BW and pen dry matter intake (DMI) were recorded monthly. Rate of feed disappearance was determined on d 5/6, 53/54, 104/105, and 117/118. Pen was the experimental unit for all analyses. The model included the fixed effect of diet for all pre-sort analyses; post-sort analyses included the fixed effects of diet, sort, and the interaction and the random effects of pen and the interaction of diet and pen. On d 60, SWBR had greater BW than MOD ( P = 0.05), and SWBR had a greater average daily gain (ADG) from d 0 to 60 ( P = 0.05). Though there were no differences after d 28, SWBR had greater DMI d 0 to 28 ( P = 0.05). From d 60 to 88, SWBR tended to have lesser ADG than MOD ( P = 0.09). Post-sort (d 111 to 196), SWBR tended to have lesser ADG than MOD ( P = 0.06), and SORT had a greater rate of feed disappearance than NOSORT (d 117/118; P = 0.01); there were no differences on other dates (Diet: P ≥ 0.38). For final BW, there was a tendency for MOD to be greater than SWBR, and SORT tended to be greater than NOSORT (Diet: P = 0.06; Sort: P = 0.10). Pre- and post-sort ruminal pH had no treatment by day differences ( P ≥ 0.77). LA incidence averaged 25%, though rate was not affected by diet, sorting, or the interaction ( P ≥ 0.16). Overall, there were no dietary differences in feed disappearance rates, though SORT steers had greater rate of feed disappearance than NOSORT steers on d 117/118. Nominal differences in feeding behavior were noted and including Sweet Bran in the diet was beneficial in the growing period as cattle adjusted to the feedlot., (© The Author(s) 2022. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Ninety-two Angus-crossbred steers (424 ± 28.3 kg initial body weight) were used in a 98-d study to assess the effects of increasing Zn supplementation on cattle performance, liver and plasma trace mineral concentrations, blood metabolites, and carcass characteristics. All steers were implanted with a Component TE-200 (200 mg trenbolone acetate + 20 mg estradiol; Elanco Animal Health, Greenfield, IN) on d 0 and fed 300 mg‧steer -1 ‧d -1 of ractopamine hydrochloride (Zoetis, Parsippany, NJ) from d 70 to 98. Cattle were fed via GrowSafe bunks (GrowSafe Systems Ltd., Airdrie, AB, Canada), and steer served as the experimental unit ( n  = 22 or 23 steers/treatment). Supplemental Zn was administered through the diet at 0, 100, 150, or 180 mg Zn/kg on a dry matter basis from ZnSO 4 (Zn0, Zn100, Zn150, or Zn180, respectively). Cattle were weighed on d -1, 0, 9/10, 20, 41, 59, 69, 70, 78/79, 97, and 98. Blood was collected on d 0, 9/10, 69, 78/79, and 97, and liver biopsies on d 9/10 and 78/79 ( n  = 12 steers/treatment). Data were analyzed as a complete randomized design. Contrast statements were formed to test the linear, quadratic, and cubic effects of Zn supplementation and test Zn0 vs. Zn supplementation. Day 10 and 70 body weight (BW) and d 0 to 10 and 0 to 70 average daily gain were linearly increased with Zn supplementation ( P  ≤ 0.05), and greater for Zn supplemented steers ( P  ≤ 0.03). No effects of Zn supplementation were observed on final BW, dressing percentage, ribeye area, 12th rib fat, or marbling ( P  ≥ 0.11). Hot carcass weight tended to be 7 kg greater for Zn supplemented steers than Zn0 ( P  = 0.07), and yield grade linearly increased with increasing Zn supplementation ( P  = 0.02). Day 10 liver Mn concentrations tended to quadratically decrease ( P  = 0.08) with increasing Zn supplementation, though d 79 liver Mn concentrations and arginase activity were not influenced by Zn ( P  ≥ 0.28). Day 10 liver arginase activity tended to be ( r  = 0.27; P  = 0.07) and d 10 serum urea nitrogen was correlated with d 10 liver Mn ( r  = 0.55; P  < 0.0001). Zinc supplementation linearly increased d 10 liver Zn and d 10, 69, 79, and 97 plasma Zn concentrations ( P  ≤ 0.05). A cubic effect of Zn was observed on d 79 liver Zn ( P  = 0.01) with lesser liver Zn in Zn0 and Zn150 steers. These data suggest increasing dietary Zn improves growth directly following the administration of a steroidal implant and that steroidal implants and beta agonists differ in their effects on protein metabolism., (© The Author(s) 2022. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Seventy-two Angus-crossbred steers (411 ± 16 kg) were assigned to a 2 × 3 factorial arrangement of treatments to examine the effects of blended Zn source supplementation on performance, carcass characteristics, and trace mineral parameters of steers administered no implant or a two-implant program. Factors included implant (IMP) strategies and Zn supplementation. During the 126-d study, steers were either not implanted (NoIMP) or implanted (IS/200; Elanco, Greenfield, IN) on days 0 (Component TE-IS; 80 mg trenbolone acetate + 16 mg estradiol) and 57 (Component TE-200; 200 mg trenbolone acetate + 20 mg estradiol). All steers were fed 70 mg Zn/kg on a dry matter (DM) basis from ZnSO 4 + 30 mg Zn/kg DM from either basic ZnCl (Vistore Zn, Phibro Animal Health, Teaneck, NJ), Zn glycinate (Gemstone Zn, Phibro Animal Health), or ZnSO 4 (ZnB, ZnG, or ZnS, respectively). Steers were blocked by weight into pens of 6 and fed a dry rolled corn-based diet via GrowSafe bunks (GrowSafe Systems Ltd.; Airdrie, AB, Canada). Data were analyzed using the Mixed Procedure of SAS, with fixed effects of Zn, IMP, and the interaction. Steer was the experimental unit ( n = 12 steers/treatment). Liver and muscle collected on days -5, 14, 71, and 120 were analyzed for Zn concentration, and data were analyzed as repeated measures (repeated effect = Day). An IMP × Zn tendency ( P = 0.07) was observed for day 126 body weight with no effects of Zn within NoIMP, whereas ZnS tended to be heavier than ZnB with ZnG intermediate within IS/200. Carcass-adjusted overall feed efficiency (G:F) was greatest for ZnS (Zn; P = 0.02). Implanted cattle had greater DM intake, G:F, and carcass-adjusted performance ( P ≤ 0.01). Liver Zn concentrations were greater for IS/200 by day 120 (IMP × Day; P = 0.02). Within IS/200, ZnG tended to have greater muscle Zn than ZnS, whereas ZnB was intermediate (Zn × IMP; P = 0.09). No Zn or IMP × Zn ( P ≥ 0.12) effects were observed for carcass data. However, IS/200 had greater hot carcass weight, dressing percentage, and ribeye area than NoIMP ( P ≤ 0.001). These data suggest that implants improve growth and influence Zn metabolism. Future work should examine Zn sources and supplementation alongside implant strategies., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Angus-crossbred steers ( n = 180; 292 ± 18 kg) from a single ranch were used to investigate the effects of a novel rumen-protected folic acid (RPFA) supplement on feedlot performance and carcass characteristics. On d 0, steers were blocked by body weight to pens (5 steers/pen), and pens within a block were randomly assigned to dietary treatments ( n = 6 pens/treatment): target intake of 0 (CON), 30 (RPFA-30), 60 (RPFA-60), 90 (RPFA-90), 120 (RPFA-120), or 150 (RPFA-150) mg RPFA·steer -1 ·d -1 . Steers were weighed before feeding on d -1, 0, 55, 56, 86, 87, 181, and 182. Pen average daily gain (ADG), dry matter intake (DMI), and gain:feed (G:F) were calculated for growing (d 0 to 56), dietary transition (d 56 to 87), finishing (d 87 to 182), and overall (d 0 to 182). Liver and blood samples were collected from two steers/pen before trial initiation and at the end of growing and finishing. Steers were slaughtered on d 183, and carcass data were collected after a 48-h chill. Data were analyzed as a randomized complete block design using ProcMixed of SAS 9.4 (fixed effects of treatment and block; experimental unit of pen). Liver abscess scores were analyzed using the Genmod Procedure of SAS 9.4. Contrast statements assessed the polynomial effects of RPFA. Supplemental RPFA linearly increased plasma folate at the end of growing and finishing ( P < 0.01), and linearly decreased plasma glucose at the end of growing ( P = 0.01). There was a cubic effect of RPFA on liver folate at the end of growing ( P = 0.01), driven by lesser concentrations for RPFA-30, RPFA-60, and RPFA-150. Growing period ADG and G:F were greatest for CON and RPFA-120 (cubic P ≤ 0.03). Transition period DMI was linearly increased due to RPFA ( P = 0.05). There was a tendency for a cubic effect of RPFA on the percentage of livers with no abscesses ( P = 0.06), driven by a greater percentage of non-abscessed livers in RPFA-30 and RPFA-60. Despite supplementing 1 mg Co/kg DM, and regardless of treatment, plasma vitamin B12 concentrations were low (<200 pg/mL), which may have influenced the response to RPFA as vitamin B12 is essential for recycling of folate., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The objective of this study was to determine the effects of increased supplemental Zn from differing sources on growth performance of steers fed diets differing in net energy. Angus steers ( n = 72, 324 ± 2.1 kg) with Genemax gain scores of 3, 4, or 5 were blocked by BW and stratified by Genemax gain score into 12 pens of 6 steers each for 158 d. Pens were randomly assigned to 1 of 3 Zn treatments (ZNTRT): 1) control (no supplemental Zn, analyzed 33 mg Zn/kg DM; CON); 2) inorganic Zn (CON + 120 mg supplemental Zn/kg DM as ZnSO 4 for entire trial; INZN); or 3) 120 mg supplemental Zn/kg DM as Zn-amino acid complex (Availa-Zn; Zinpro, Eden Prairie, MN) for first 60 d, then a blend of ZnSO 4 and Zn-AA complex (CON + 60 mg supplemental Zn/kg DM as ZnSO 4 + 60 mg supplemental Zn/kg DM as Zn-amino acid complex) for the remainder of the trial (ZNBLD). Two dietary energy strategies (ENERGY) were formulated to reach ADG rates of 1) 1.6 kg/d (LE) or 2) 2.0 kg/d (HE) utilizing a 3 × 2 factorial arrangement (12 steers/treatment). All steers were fed LE for a 60 d growing period, then pens were randomly assigned to ENERGY treatments fed the remaining 91 d. Day 60 BW tended to be greater ( P = 0.07) in steers receiving supplemental Zn vs. CON. Liver Cu was decreased in Zn supplemented steers vs. CON ( P = 0.02). Liver Zn concentrations on d 56 did not differ for Zn vs. CON ( P = 0.22) nor were there differences due to Zn source ( P = 0.98). There were or tended to be ZNTRT × ENERGY effects for d 67-90 ADG and G:F ( P ≤ 0.01), and d 122 BW and d 90-122 G:F ( P ≤ 0.10) driven by improved performance for ZNBLD-HE over ZNBLD-LE, while ENERGY within CON and INZN did not differ. Day 90-122 ADG, overall ADG and overall G:F was greater ( P ≤ 0.02) and d 67-90 G:F tended to be greater ( P = 0.10) for HE vs. LE. No ZNTRT × ENERGY or ZNTRT effects were detected for HCW, REA, BF, KPH, MS, or YG ( P ≥ 0.37) while HE increased HCW, BF, MS, and YG compared with LE ( P ≤ 0.05). In the liver, ZNTRT affected d 97 MT1A expression ( P = 0.03) where INZN was greater than ZNBLD or CON ( P ≤ 0.02), while ZIP14 was unaffected due to ZNTRT, ENERGY, or the interaction ( P ≥ 0.39). Supplying supplemental Zn as ZNBLD during the transition period appeared to improve performance measures, but no final performance advantages were noted due to increased supplemental Zn, regardless of source. Additionally, differences in liver MT1A expression may indicate differing post-absorptive metabolism between Zn sources., (© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The objective of this study was to evaluate growth performance, carcass characteristics, and plasma amino acid profiles of feedlot steers fed rumen-protected Lys. Forty-two Angus-cross steers (304 ± 25 kg) were blocked by weight and fed treatment diets for 180 d (growing days 0 to 55; finishing days 56 to 180): 1) Lys-deficient diet (CON; n = 12 steers), 2) Lys-adequate diet containing soybean meal (POS; n = 12 steers), or 3) Lys-deficient diet plus supplemental rumen-protected Lys (RPL; AjiPro-L; Ajinomoto Animal Nutrition North America, Eddyville, IA; n = 18 steers). Consecutive day bodyweights (BWs) were recorded to begin and end growing and finishing. Individual steer dry matter intake (DMI) was recorded. Blood was collected on days 0, 56, and 179 for analysis of physiological free amino acids. Steers were harvested on day 180 and carcass characteristics were recorded. Data were analyzed using Proc Mixed of SAS 9.4. Steer was the experimental unit and treatment was the fixed effect for all parameters. Block was a fixed effect for growth performance, feed intake, and carcass data. The day 0 value for each parameter of physiological free amino acids was used as a covariate during analysis. The CON steers had greater BW, average daily gain (ADG), and gain to feed (G:F) at the end of growing (day 56; P ≤ 0.05) vs. POS and RPL. The CON steers also had greater final BW ( P = 0.04) and overall ADG ( P = 0.04) than RPL, while POS was intermediate. Carcass characteristics were not different across treatments [hot carcass weight, dressing percent, ribeye area, back fat, kidney/pelvic/heart (KPH) percent, marbling, or calculated yield grade; P ≥ 0.13]. Plasma urea N was greater in POS steers on days 56 and 179 ( P ≤ 0.04). Plasma Lys and Arg concentrations were greater in POS at day 56 ( P ≤ 0.02); however, there was no difference among treatments for these two variables at day 179 ( P ≥ 0.44). Steers in all treatments had greater DMI than predicted, causing a negative metabolizable Lys balance for all treatments during growing. Though the metabolizable Lys balance was positive for POS and RPL-fed steers during finishing, the increased metabolizable Lys in these treatments may have decreased performance if other amino acids were imbalanced due to increased intakes., (© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Forty-eight newly weaned crossbred beef steers from a single-source were used to determine the effects of feeding a Saccharomyces cerevisiae fermentation product (SCFP; NaturSafe, Diamond V) on receiving period performance, nutrient digestibility, and antioxidant defense. Seven days after arrival, steers were stratified by BW (257 ± 18 kg), sorted into pens ( n = 1 pen/treatment), and pens assigned to dietary treatments: SCFP at 0 (CON), 12 (SCFP12), 18 (SCFP18), or 0 g·steer -1 ·d -1 during preconditioning (PRE; days -19 to 0), then 18 g·steer -1 ·d -1 during receiving (REC; days 0 to 58; CON18). On day -1 BW and blood were collected, steers were loaded onto a semitruck and transported 1,748 km over 19 h. Upon return, steers were weighed, stratified by BW within treatment and sorted into pens with GrowSafe bunks ( n = 12 steers/treatment). Steers were weighed on days -1, 0, 29, 30, 57, and 58. Blood was collected from all steers on days -1, 1, and 8 and liver biopsies were performed on all steers on days -20, -3, and 59. Titanium dioxide was included as an indigestible marker in the diet of all steers from days 14 through 29 to determine total tract nutrient digestibility. Data were analyzed as a completely randomized design using ProcMixed of SAS with the fixed effect of treatment. Steer was the experimental unit for REC period variables. Contrast statements compared the linear and quadratic effects of feeding SCFP throughout the trial (CON, SCFP12, and SCFP18) and the effect of supplementation at 18 g·steer -1 ·d -1 for the entire trial or starting in REC (SCFP18 vs. CON18). Steers fed SCFP12 exhibited the greatest ADG and G:F from days 0 to 30 (quadratic P ≤ 0.04). Total tract digestibility of NDF and ADF was linearly decreased by SCFP (linear P ≤ 0.03). On day -3, SCFP12-fed steers tended to have the greatest liver concentrations of total, oxidized, and reduced glutathione (quadratic P = 0.06). Red blood cell lysate Mn:total-superoxide dismutase activity was 16% greater 1 d posttransit compared with pretransit values (day P ≤ 0.01). Timing of SCFP supplementation (SCFP18 vs. CON18) did not affect any of the variables assessed herein ( P ≥ 0.19). Supplementing SCFP at 12 g·steer -1 ·d -1 tended to affect antioxidant capacity prior to transit and improved early receiving period performance; however, overall receiving period performance was not affected by SCFP supplementation. Further research is necessary to determine the optimal dose and timing of SCFP supplementation for beef cattle., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The objective was to determine if zinc (Zn) retention improved with supplemental Zn above recommended concentrations with increasing dietary fiber concentration. Angus steers ( n = 32; 309 ± 4.2 kg body weight [BW]) with GeneMax gain scores of 3, 4, or 5 were utilized in a 2 × 2 factorial arrangement (8 steers per treatment). Steers were stagger started (four blocks of eight steers) and stratified by BW within growing diets to one of two Zn strategies (ZNTRT), no supplemental Zn (analyzed 36 mg Zn/kg dry matter [DM]; CON) or supranutritional Zn (CON + 60 mg Zn/kg DM as ZnSO 4 + 60 mg Zn/kg DM as Zn-amino acid complex; SUPZN). Dietary fiber strategies (FIBER) were formulated to target two fiber supplementation rates representing high fiber (HF; ~35% neutral detergent fiber [NDF]) or low fiber (LF; ~25% NDF). Within block, steers received HF for 60 d; then pens were randomly assigned to LF or HF for finishing. Steers fed LF were transitioned for 15 d; on day 75, steers were moved to metabolism crates and adapted for 10 d, followed by 5 d of total fecal and urine collection. Retention of Zn, Mn, Fe, Cu, and N were calculated. The model for analysis of metabolism data included the fixed effects of ZNTRT, FIBER, block, and the interaction of ZNTRT × FIBER, with the three-way interaction of ZNTRT × FIBER × block as random. Steer was the experimental unit ( n = 8 per treatment combination). Zinc did not affect initial 60-d performance ( P ≥ 0.62). DM and organic matter digestibility were lesser ( P = 0.02) and N digestibility tended to be lesser ( P = 0.07) in CON vs. SUPZN. Intake and digestibility of NDF and acid detergent fiber were greater ( P ≤ 0.01) in HF vs. LF. Digestibility and retention of N as a percentage of intake were greater ( P ≤ 0.04) whereas N retention as grams per day tended to be greater in HF vs. LF ( P = 0.06). Apparent absorption of Zn tended to be greater ( P = 0.06) in CON vs. SUPZN. A ZNTRT × FIBER effect was identified for Zn retention (milligrams per day; P = 0.01) where within SUPZN Zn retention was greater in HF vs. LF ( P < 0.01). Apparent absorption and retention of Zn were greater (% of intake; P ≤ 0.02) in HF vs. LF. Apparent absorption of Cu, Fe, and Mn was unaffected by ZNTRT or FIBER ( P ≥ 0.24). Increasing dietary Zn increased Zn retained regardless of changes in coefficient of absorption. In addition, dietary fiber content may impact trace mineral and N metabolism by steers, potentially due to increased release of these nutrients from feed as fiber digestibility increases. It appears dietary Zn concentrations and diet composition influence trace mineral absorption in beef steers., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science.)