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NUTRITION: Original Research| Volume 37, ISSUE 6, P722-732, December 2021

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Effects of feedlot bunk management and bulk density of steam-flaked corn on growth performance, carcass characteristics, and liver score of finishing beef steers fed high-concentrate diets without by-products or tylosin phosphate

      ABSTRACT

      Objective

      Our objective was to evaluate effects of bunk management strategy and bulk density of steam-flaked corn (SFC) on growth performance, carcass characteristics, and incidence and severity of liver abscesses in finishing beef steers fed diets without tylosin phosphate.

      Materials and Methods

      Beef steers (n = 192; initial BW = 332 ± 8.1 kg) were used in a randomized complete block design comprised of 12 BW blocks and 12 pen replications per treatment. A 2 × 2 factorial arrangement of treatments was used: (1) slick-bunk management + 335 g/L SFC-based diets (SFC); (2) modified ad libitum bunk management + 335 g/L SFC; (3) slick-bunk management + 425 g/L SFC; (4) modified ad libitum bunk management + 425 g/L SFC.

      Results and Discussion

      Bunk management strategy did not affect growth performance, carcass characteristics, or liver abscess score (P ≥ 0.10). The ADG of steers fed 425 g/L SFC was greater (P = 0.05) from d 35 to 105 than those fed 335 g/L SFC; however, overall ADG was not different (P = 0.36). The DMI of steers fed 425 g/L SFC was greater at each interim period (P ≤ 0.05) and overall (P ≤ 0.01) than those fed 335 g/L SFC. Gain-to-feed (G:F) of steers fed 425 g/L SFC tended (P = 0.10) to be lesser from d 0 to 35 but was not different overall (P = 0.12). Steers fed 425 g/L SFC tended to have greater backfat and calculated empty body fat percentage (P ≤ 0.07) than those fed 335 g/L SFC and greater calculated YG (P = 0.05). Steers fed 425 g/L SFC had 43.5% fewer (P = 0.04) liver abscesses than those fed 335 g/L SFC, but liver abscess severity did not differ (P ≥ 0.12).

      Implications and Applications

      Bunk management did not affect growth performance, carcass characteristics, or development of liver abscesses. Steers fed 425 g/L SFC-based diets had greater DMI and 43.5% fewer liver abscesses than those fed 335 g/L SFC-based diets with similar overall G:F, but carcasses were fatter. Greater bulk density of SFC may be a useful management strategy and a viable antimicrobial alternative to decrease liver abscesses.

      Key words

      INTRODUCTION

      Bunk management and accurate feed delivery are the primary components to management of clinical and subclinical metabolic disorders (
      • Pritchard R.H.
      • Bruns K.W.
      Controlling variation in feed intake through bunk management..
      ). Large daily DMI variation and irregular feeding behaviors are commonly implicated in diagnosis of metabolic disorders (
      • Schwartzkopf-Genswein K.S.
      • Beauchemin K.A.
      • Gibb D.J.
      • Crews Jr., D.H.
      • Hickman D.D.
      • Streeter M.
      • McAllister T.A.
      Effect of bunk management on feeding behavior, ruminal acidosis and performance of feedlot cattle: A review..
      ), a leading cause of feedlot mortality (

      USDA-NAHMS. 2011. United States Department of Agriculture-National Animal Health Monitoring System. Feedlot 2011. Part 1: Management Practices on U.S. Feedlots with a Capacity of 1,000 or More Head. Accessed Oct. 2020. https://www.aphis.usda.gov/animal_health/nahms/feedlot/downloads/feedlot2011/Feed11_dr_PartI_1.pdf.

      ). Likewise, subclinical acidosis may induce rumenitis, leading to decreased G:F and formation of liver abscesses (
      • Owens F.N.
      • Secrist D.S.
      • Hill W.J.
      • Gill D.R.
      Acidosis in cattle: A review..
      ). Slick-bunk management is widely used in the feedlot industry to facilitate ease of bunk management, as it is believed to result in greater DMI throughout the feeding period and to reduce overconsumption leading to metabolic disorders (
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      ;
      • Pritchard R.H.
      • Bruns K.W.
      Controlling variation in feed intake through bunk management..
      ).
      In the United States, corn is the predominant cereal grain in feedlot diets (
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      ;

      Galyean, M. L., and J. F. Gleghorn. 2001. Summary of the 2000 Texas Tech University Consulting Nutritionist Survey. Texas Tech University Burnett Center Progress Report No. 12. Accessed Jul. 27, 2021. https://www.depts.ttu.edu/afs/burnett_center/progress_reports/bc12.pdf.

      ;
      • Vasconcelos J.T.
      • Galyean M.L.
      Nutritional recommendations of feedlot consulting nutritionists: The 2007 Texas Tech University survey..
      ;
      • Samuelson K.L.
      • Hubbert M.E.
      • Galyean M.L.
      • Löest C.A.
      Nutritional recommendations of feedlot consulting nutritionists: The 2015 New Mexico State and Texas Tech University survey..
      ).
      • Zinn R.A.
      Influence of flake density on the comparative feeding value of steam-flaked corn for feedlot cattle..
      observed a linear increase in the extent of ruminal and total-tract starch digestion of steam-flaked corn (SFC) with an increased degree of processing by increasing roll pressure to produce lighter flake density. Although heat and pressure treatment improve starch availability of cereal grains and subsequent growth performance of cattle, the risk of developing metabolic disorders such as acidosis, rumenitis, and formation of liver abscesses are concomitantly increased (
      • Owens F.N.
      • Secrist D.S.
      • Hill W.J.
      • Gill D.R.
      Acidosis in cattle: A review..
      ). Cattle may develop liver abscesses during any production phase; however, prevalence and economic impact is greatest in the feedlot industry (
      • Amachawadi R.G.
      • Nagaraja T.G.
      Liver abscesses in cattle: A review of incidence in Holsteins and of bacteriology and vaccine approaches to control in feedlot cattle..
      ). Incidence of liver abscess at harvest for most feedlots is 12 to 32% and represents a major economic liability to the feeder, packer, and consumer (
      • Nagaraja T.G.
      • Chengappa M.M.
      Liver abscesses in feedlot cattle: A review..
      ).
      Bunk management and degree of corn processing affect DMI and growth performance of finishing beef cattle. Therefore, the study objective was to determine the effects of bunk management strategy and bulk density of SFC on growth performance, carcass characteristics, and liver abscess incidence in finishing beef cattle fed diets without tylosin phosphate.

      MATERIALS AND METHODS

      All live animal procedures were approved by the Texas Tech University Animal Care and Use committee before study initiation (ACUC #19094–11). The experiment was conducted from January 2020 to July 2020 at the Texas Tech University Burnett Center for Beef Cattle Research and Instruction, located 9.7 km east of New Deal, Texas.

      Animals, Arrival Processing, and Management

      Two-hundred four Bos taurus steers (arrival BW = 299 ± 26.2 kg) were sourced from a ranch in Southeast Colorado and transported approximately 8 h to the experimental location on December 12, 2019. Before arriving at the experimental location, the cattle had been weaned, castrated, and backgrounded for 30 d (details unknown). Steers rested overnight and were provided access to water and long-stem grass hay. The following morning, steers were individually weighed (Silencer hydraulic squeeze chute; Moly Manufacturing; Avery Weigh-Tronix load cells; readability ± 0.454 kg; scale calibrated with 454 kg of certified weights before use), affixed with an individually identifiable ear tag, administered an oral (Safeguard, Merck Animal Health) and transdermal (Dectomax, Zoetis) anthelmintic for treatment of internal and external parasites, and vaccinated against viral respiratory (Vista 5, Merck Animal Health), clostridial (Vision 8 with SPUR, Merck Animal Health), and Mycoplasma bovis (Myco-B One Dose, American Animal Health) pathogens. Steers were housed in soil-surfaced outdoor pens with partial shade during the 3-wk adaptation period and fed a 65% concentrate starter diet. Steers transitioned to the finishing diet using a 4-step process of 65, 70, 77, and 94% concentrate diets, where each interim diet was fed for 7 d. During this time, steers were moved from the soil-surfaced pens to acclimate to concrete-surfaced pens. On d 0, steers were consuming the final 94% concentrate diet. Day 0 was January 20, 2020. Throughout the study, the maximum observed temperature was 43.8°C, the minimum observed temperature was −10.5°C, and the average temperature was 18.2°C. Total precipitation was 223.8 mm and the average humidity was 45%.
      Before the experiment began, steers were administered a time-release implant containing 200 mg of trenbolone acetate + 40 mg of estradiol 17β (Revalor-XS, Merck). Steers were housed in concrete-surfaced pens with partially slotted floors providing 15.95 m2 of pen space and 60 cm of linear bunk space per animal (4 steers/pen). Each pen was equipped with automatic waterers, with float-action water supply, shared by adjacent pens. The cattle had no access to shade within the pens. On days when the temperature was exceeded 32°C, cattle were sprinkled with water once per hour until the temperature dropped below this threshold.
      All steers were treated for lice using a transdermal insecticide on d 35 (Cyclence, Bayer Animal Health) and 105 (Dectomax, Zoetis). Implant retention was confirmed via ear palpation on d 35. All implants were retained, and abscess rate was 2.5%. Body weight was individually measured on d 0 (initial), 35, 105, and 140. The d-70 BW measures were not completed because of the pandemic restrictions on campus research activity. Final BW was collected on d 162 (6 blocks) or 190 (6 blocks). A 4% shrink was applied to all BW.

      Treatment Application

      The randomized complete block design consisted of 12 BW blocks and 12 pen replications per treatment with pen as the experimental unit for all dependent variables. Experimental treatments were randomly assigned to pen within block and arranged in a 2 × 2 factorial: (1) slick-bunk management + 335 g/L (26 lb/bu) SFC-based diet, or (2) modified ad libitum bunk management + 335 g/L (26 lb/bu) SFC-based diet, or (3) slick-bunk management + 425 g/L (33 lb/bu) SFC-based diet, or (4) modified ad libitum bunk management + 425 g/L (33 lb/bu) SFC-based diet.

      Bunk Management

      Bunks were monitored for residual feed at 0700 and 1600 h daily. Separate individuals executed each respective bunk management method. A bunk scoring system (Table 1) adapted and modified from

      Pritchard, R. H. 1993. Bunk management. Proceedings. Land O’Lakes Delivering the Difference Conference. Accessed Jul. 27, 2021. http://gpvec.unl.edu/Elective_files/feedlot/BunkMgt_101_RP.pdf.

      was used to indicate bunk conditions at both reading times. At 1600 h, a bunk score 2 was targeted for both treatments. For slick-bunk management, a bunk score 0 or 1/2 was targeted at 0700 h. For modified ad libitum management, a bunk score 1 or 1 1/2 was targeted at 0700 h. If the bunk was scored 2 or greater, the feed delivery was decreased equally to the visual estimate of residual feed. If the bunk was scored less than 1, the daily feed delivery was increased 0.70 kg/animal as-fed to achieve some day-to-day residual feed carryover. For slick-bunk management at the 0700-h bunk read, the targeted bunk score of 0 or 1/2 was achieved 55% of the time, score of 1 for 21% of the time, score of 1 1/2 for 22% of the time, and score of 2 for 2% of the time. Likewise, the targeted bunk score of 1 or 1 1/2 at 0700 h for modified ad libitum management was achieved 59% of the time, and bunks were scored 0 for 19% of the time, 1/2 for 19% of the time, and 2 for 3% of the time.
      Table 1Bunk scoring system used throughout the experiment
      Adapted and modified from Pritchard (1993).
      ItemDescription
      0No feed remaining in bunk; slick

      0730 h target for slick-bunk management
      1/21 to 2% of previous day’s feed remaining
      1Up to 5% of previous day’s feed remaining

      0730 h target for modified ad libitum bunk management
      1 1/25% to 15% of previous day’s feed remaining
      215% to 50% of previous day’s feed remaining
      3>50% of previous day’s feed remaining, crown on feed is disturbed
      4Feed is virtually untouched, crown on feed is undisturbed
      1 Adapted and modified from

      Pritchard, R. H. 1993. Bunk management. Proceedings. Land O’Lakes Delivering the Difference Conference. Accessed Jul. 27, 2021. http://gpvec.unl.edu/Elective_files/feedlot/BunkMgt_101_RP.pdf.

      .
      Basal diet was the same regardless of bulk density treatment assignment, and only differed in the bulk density of SFC (Table 2). Diets were formulated to meet requirements for growing and finishing beef cattle (

      NASEM. 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ). All diets included 31.9 mg/kg DM monensin sodium (Rumensin 90, Elanco Animal Health). Steers were fed once daily beginning at 0800 h. Diets were mixed in a paddle-type mixer and conveyed to a tractor pulled mixer (Rotomix 84–8 wagon mixer; Rotomix; scale readability ± 0.45 kg). The diets were sampled 3 times each week throughout the study and composited by week. The weekly sample was divided by one-half and the first subsample was used to determine DM in a forced-air oven at 100°C for 24 h (The Grieve Corporation). The DM was used to calculate total DMI for each week. The second subsample was used for chemical analyses of CP, ADF, NDF, fat, starch, and ash content. On days when BW was collected, or when feed spoilage occurred, orts were collected, weighed, and dried in a forced-air oven as described previously. Data from measurement of orts were used to compute DMI.
      Table 2Ingredient and nutrient composition of the experimental diets where bulk density of steam-flaked corn varied
      The average weekly DM of the 335 g/L-steam-flaked corn-based diet was 83.2% and DM of 425 g/L steam-flaked corn-based diet was 82.9%.
      ItemFinishing diet
      Ingredient, %
       Steam-flaked corn78.95
       Alfalfa hay6.50
       Cottonseed meal4.25
       Cane molasses3.50
       Yellow grease2.50
       Limestone1.35
       Urea0.95
       Supplement
      Supplement supplied 5.99% potassium chloride, 44.40% CP, 3.82% sodium, 8.34 mg/kg cobalt carbonate, 395.00 mg/kg copper sulfate, 408.00 mg/kg iron sulfate, 764 mg/kg manganous oxide, 2.92 mg/kg selenium, and 2,490.00 mg/kg zinc sulfate on a DM basis.
      2.00
      Analyzed nutrient composition
      Analysis performed by ServiTech Laboratories (Amarillo, TX).
       CP, %12.25
       NDF, %11.75
       ADF, %7.20
       Fat, %4.95
       Ca, %0.46
       P, %0.26
       NEm,
      Tabular values based on Beef Cattle Nutrient Requirements Model (NASEM, 2016).
      Mcal/kg
      2.11
       NEg,
      Tabular values based on Beef Cattle Nutrient Requirements Model (NASEM, 2016).
      Mcal/kg
      1.45
      1 The average weekly DM of the 335 g/L-steam-flaked corn-based diet was 83.2% and DM of 425 g/L steam-flaked corn-based diet was 82.9%.
      2 Supplement supplied 5.99% potassium chloride, 44.40% CP, 3.82% sodium, 8.34 mg/kg cobalt carbonate, 395.00 mg/kg copper sulfate, 408.00 mg/kg iron sulfate, 764 mg/kg manganous oxide, 2.92 mg/kg selenium, and 2,490.00 mg/kg zinc sulfate on a DM basis.
      3 Analysis performed by ServiTech Laboratories (Amarillo, TX).
      4 Tabular values based on Beef Cattle Nutrient Requirements Model

      NASEM. 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      .

      Steam Flaking and Enzymatic Starch Availability Analysis

      Whole corn grain was transported via auger to a vertical chest (2,268 kg capacity), where steam and a surfactant (Mycoflake, Kemin Industries) were applied at atmospheric pressure for approximately 30 min at 93°C, decreasing the DM content of the whole corn from 88.16% DM to 80.63% DM after the steam flaking process, adding (8.5% moisture). Whole corn then passed through a roller mill (46 × 61 cm) with roll tension set accordingly to produce either 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu) flake bulk density, which was confirmed using a hand-type density tester (Seedburo Equipment Company). Steam-flaked corn of each bulk density was transported from the roller mill to individual, enclosed bulk bins via an air-lift system for storage. Steam-flaked corn was prepared 3 to 4 d per week for the duration of the study, and diets were mixed each morning as described previously. A sample of each bulk density was collected every 30 min during the steam flaking process directly beneath the roller mill. Samples, inclusive of flake and fines, were air-dried in a single, uniform layer for 24 h then frozen at −20°C for subsequent analysis of total and enzymatically available starch.
      Total and enzymatically available starch (Table 3) analysis was conducted in duplicate according to
      • Xiong Y.
      • Bartle S.J.
      • Preston R.L.
      Improved enzymatic method to measure processing effects and starch availability in sorghum grain..
      and modified to accommodate use of a biochemistry analyzer (2700D Select Biochemistry Analyzer, YSI Life Sciences). Samples were thawed and dried in a forced-air oven at 45°C for approximately 14 h, allowed to air-equilibrate, then ground in a Wiley mill (Thomas-Wiley Laboratory Mill Model 4, Arthur H. Thomas Co.) to pass a 1-mm screen before analysis. To determine total starch, 0.2 g of the ground sample was placed in a 50-mL digestion vial with 30 mL of acetate buffer solution (pH 4.50 ± 0.05), then placed in a 94°C reciprocating water bath for 75 min to gelatinize the starch. Following incubation, vials were cooled in an ice bath for 20 min then 1 mL of amyloglucosidase working solution [concentrated amyloglucosidase solution (ServiTech) diluted with acetate buffer solution to dispense 200 KU of enzyme per 1 mL of working solution] was added. Vials were then incubated at 40°C for 75 min in a reciprocating water bath, after which 4 mL of 10% (wt∙vol−1) zinc sulfate solution and 2 mL of 0.5 mol sodium hydroxide solution were added, and each vial was diluted to 50 mL with deionized water. Each suspension was gravity-filtered passing through Q5 filter paper (Fisher Scientific). Filtrate was analyzed for d-glucose. Samples for determination of available starch were prepared and analyzed in the same manner as those for total starch, excluding the initial gelatinization of starch. Powdered crystalline glucose (product A16828, Fisher Scientific) and purified corn starch (product S9679, Millipore-Sigma) were used as internal reference standards. Percentage total starch was 89.3 ± 1.82% for corn starch and 91.3 ± 2.35% for glucose.
      Table 3Analyzed total and enzymatically available starch of steam-flaked corn (SFC) processed to varying bulk densities on a DM basis
      Mean ± SD; n = 20 samples/mean for 335 g/L SFC and n = 19 samples/mean for 425 g/L SFC. Acceptable CV among duplicates was ≤3%.
      Item335 g/L425 g/L
      Total starch, %74.8 ± 1.8972.3 ± 2.19
      Enzymatic starch

       availability, %
      65.0 ± 4.1836.5 ± 3.92
      DM,
      Dried in a forced-air oven at 45°C for 14 h.
      %
      92.1 ± 0.6691.5 ± 0.41
      1 Mean ± SD; n = 20 samples/mean for 335 g/L SFC and n = 19 samples/mean for 425 g/L SFC. Acceptable CV among duplicates was ≤3%.
      2 Dried in a forced-air oven at 45°C for 14 h.

      Carcass Data

      Steers were fed to equal back fat (similar degree of finish) by visual appraisal, then transported to a commercial abattoir for slaughter. The 12 blocks of steers were slaughtered on 2 dates (blocks 1 to 6 were slaughtered after 162 d on feed and blocks 6 to 12 were slaughtered after 191 d on feed). Within block, each treatment was represented one time to prevent confounding of treatment and slaughter date. Individual carcass measurements and liver scores were collected by plant personnel. Liver scores are described subsequently as normal = edible; A− = 1 to 2 small abscesses or inactive scars; A = 1 to 2 large abscesses, or multiple small abscesses; or A+ = multiple large abscesses (
      • Brink D.R.
      • Lowry S.R.
      • Stock R.A.
      • Parrott J.C.
      Severity of liver abscesses and efficiency of feed utilization of feedlot cattle..
      ;
      • Brown T.R.
      • Lawrence T.E.
      Association of liver abnormalities with carcass grading performance and value..
      ). Quality and yield grades were determined by plant personnel using the E+V image analysis system described by
      • Shackelford S.D.
      • Wheeler T.L.
      • Koohmaraie M.
      On-line prediction of yield grade, longissimus muscle area, preliminary yield grade, adjusted preliminary yield grade, and marbling score using the MARC beef carcass image analysis system..
      . The ADG and G:F were calculated on a BW and carcass-adjusted basis. Final BW was carcass-adjusted by dividing the hot carcass weight by the overall average DP (66.15%). Carcass-adjusted ADG was calculated by subtracting the initial BW from the carcass-adjusted final BW, then divided by days on feed. The G:F (live basis) was computed as the quotient of ADG divided by daily DMI. The carcass-adjusted G:F was calculated by dividing the carcass-adjusted ADG by the d 0 to final DMI. Dry matter intake/metabolic body size was calculated according to

      Kleiber, M. 1961. The Fire of Life. An Introduction to Animal Energetics. John Wiley and Sons Inc.

      . Gain energy density was calculated as retained energy divided by 0 to final ADG. Performance-adjusted net energy for maintenance and gain were calculated using a quadratic formula (
      • Zinn R.A.
      • Shen Y.
      An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves..
      ). Empty body fat was estimated from the equations of
      • Guiroy P.J.
      • Fox D.G.
      • Tedeschi L.O.
      • Baker M.J.
      • Cravey M.D.
      Predicting individual feed requirements of cattle fed in groups..
      and adjusted final shrunk BW at 28% empty body fat was estimated using equations of
      • Tylutki T.P.
      • Fox D.G.
      • Anrique R.G.
      Predicting net energy and protein requirements for growth of implanted and nonimplanted heifers and steers and nonimplanted bulls varying in body size..
      .

      Statistical Analysis

      Pen was the experimental unit for all dependent variables. Growth performance and continuous carcass variables were analyzed using PROC MIXED (SAS v9.4, SAS Institute Inc.). Bunk management strategy, bulk density of SFC, and the bunk management × bulk density interaction was included as a fixed effect, and block was included as a random effect. Categorical carcass data and liver score were analyzed as a binomial proportion using PROC GLIMMIX where bunk management strategy, bulk density of SFC, and the bunk management × bulk density interaction were fixed effects, and block was the random effect. Differences in LSM were determined using least significant difference. Treatment effects were considered statistically significant when P ≤ 0.05, and tendencies were discussed when 0.05 < P ≤ 0.10.

      RESULTS AND DISCUSSION

      No significant interactions were observed (P ≥ 0.09), thus main-effect LSM of bunk management and bulk density of SFC are reported throughout.

      Feedlot Growth Performance

      Bunk management strategy did not affect growth performance (Table 4; P ≥ 0.15) except the standard deviation of ADG within pen, which was 25.6% greater among cattle under slick-bunk management from d 35 to 105 than those under modified ad libitum management (P = 0.02). Indeed, the magnitude of this variability was inconsequential as there were no further differences in growth performance attributed to bunk management strategy.
      Table 4Main effects of bunk management and bulk density of steam-flaked corn on live and carcass-adjusted growth performance of finishing beef steers
      Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.24).
      ItemBunk managementP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      Flake densityP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      SEM
      Pooled standard error of LSM (n = 24 pens/mean).
      ALS335 g/L425 g/L
      n, steers93959395
      n, pens24242424
      Live weight basis
      Shrink (4%) was applied to all BW.
       Initial BW, kg3333310.153333310.468.1
       Final BW, kg6086050.686056090.575.8
      ADG, kg
       d 0 to 351.741.840.191.801.780.770.064
       d 35 to 1051.841.830.901.781.890.050.039
       d 105 to final1.191.150.331.181.160.620.034
       d 0 to final
      Average days on feed was 177.
      1.561.560.931.541.580.360.028
      SD of ADG, kg
       d 0 to 350.380.330.300.350.370.560.033
       d 35 to 1050.290.390.020.340.340.930.028
       d 105 to final0.270.260.950.250.280.370.030
       d 0 to final0.200.220.480.210.210.850.022
      DMI, kg
       d 0 to 357.437.490.687.307.610.030.223
       d 35 to 1058.758.760.948.528.99<0.010.160
       d 105 to final8.548.460.608.348.660.050.129
       d 0 to final8.418.390.878.218.58<0.010.143
       DMI/MBS,
      Dry matter intake/metabolic body size (MBS), g/kg; MBS calculated according to Kleiber (1961).
      g/kg
      83.1783.290.8981.5084.96<0.010.866
      Gain:feed
       d 0 to 350.2340.2460.160.2470.2330.100.0058
       d 35 to 1050.2110.2100.850.2100.2110.790.0049
       d 105 to final0.1400.1360.520.1420.1340.170.0041
       d 0 to final0.1860.1870.730.1880.1840.120.0026
       GED,
      Gain energy density, Mcal/kg. Calculated as retained energy divided by d 0 to final ADG, kg.
      Mcal/kg
      7.087.060.767.057.100.530.058
      Carcass-adjusted basis
       Final BW,
      Calculated as hot carcass weight divided by overall DP (66.15%).
      kg
      6106060.676046120.386.38
       ADG, kg1.561.560.991.541.590.220.030
       Gain:feed0.1860.1870.870.1870.1850.580.0028
      paNE,
      pa = performance adjusted. Net energy for maintenance and gain were calculated using a quadratic formula (Zinn and Shen, 1998).
      Mcal/kg
       Maintenance2.242.240.882.272.21<0.010.016
       Gain1.551.550.881.581.53<0.010.014
      Tabular NE,
      Estimated using the Beef Cattle Nutrient Requirements Modeling software (NASEM, 2016).
      Mcal/kg
       Maintenance2.112.112.112.11
       Gain1.451.451.451.45
      Observed/expected NE
      paNE/tabular NE.
       Maintenance1.061.060.881.081.05<0.010.008
       Gain1.071.070.881.091.05<0.010.010
      1 Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.24).
      2 Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      3 Pooled standard error of LSM (n = 24 pens/mean).
      4 Shrink (4%) was applied to all BW.
      5 Average days on feed was 177.
      6 Dry matter intake/metabolic body size (MBS), g/kg; MBS calculated according to

      Kleiber, M. 1961. The Fire of Life. An Introduction to Animal Energetics. John Wiley and Sons Inc.

      .
      7 Gain energy density, Mcal/kg. Calculated as retained energy divided by d 0 to final ADG, kg.
      8 Calculated as hot carcass weight divided by overall DP (66.15%).
      9 pa = performance adjusted. Net energy for maintenance and gain were calculated using a quadratic formula (
      • Zinn R.A.
      • Shen Y.
      An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves..
      ).
      10 Estimated using the Beef Cattle Nutrient Requirements Modeling software (

      NASEM. 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ).
      11 paNE/tabular NE.
      Fundamentally, bunk management manipulates cattle behavior and DMI to maximize growth performance while preventing metabolic disease including acidosis, rumenitis, and the formation of liver abscesses (
      • Pritchard R.H.
      • Bruns K.W.
      Controlling variation in feed intake through bunk management..
      ). Slick-bunk management is a common practice in cattle feeding in the United States and is used to offer the amount of feed that matches maximal feed intake by the cattle, where the bunk is slick or empty just before the next feeding time. In slick-bunk management, carryover feed is minimized, so excessive starch is unavailable which discourages overeating that can lead to metabolic disorders. True ad libitum bunk management, albeit uncommon in commercial feedlots in the United States, is achieved when the animal has unrestricted access to feed in the bunk. Modified ad libitum bunk management used in the present study attempted to limit day-to-day feed carryover to ≤5% of feed delivered (bunk score 1 at 0730 h; Table 1) to prevent feed wastage and excessive overeating that can induce metabolic disorders. Average daily feed carryover in the present experiment was approximately 8% of the previous day’s feed for modified ad libitum, although bunks were slick 38% of the time. In contrast, average daily feed carryover was 1% of the previous day’s feed for slick-bunk management, although these bunks were slick most the time as discussed previously.
      While the contribution of bunk management strategy to ADG variability is not well documented, the present study noted the SD of ADG to be greater in cattle under slick-bunk management from d 35 to 105, the period in which total ADG was greatest. The lack of differences in bunk management observed in this study is noteworthy. Many consulting nutritionists advise the use of slick-bunk management. The purported idea is that it yields maximum intake more successfully than methods that allow some degree of feed carryover because there is less inherent variation in feed delivered and DMI (

      Pritchard, R. H. 1993. Bunk management. Proceedings. Land O’Lakes Delivering the Difference Conference. Accessed Jul. 27, 2021. http://gpvec.unl.edu/Elective_files/feedlot/BunkMgt_101_RP.pdf.

      ;
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      ). Rumen microbes function best when substrate availability and ruminal pH are consistent (

      Owens, F. N., F. J. Hill, D. S. Secrist, and D. R. Gill. 1995b. Intake by feedlot cattle. Page 97 in Proceedings: 56th Minnesota Nutrition Conference and Alltech Inc. Technical Symposium. Accessed Jan. 14, 2021. https://conservancy.umn.edu/handle/11299/170624.

      ;

      Russell, J. B. 2002. Rumen Microbiology and Its Role in Ruminant Nutrition. James B. Russell, Ithaca, NY.

      ). In the present experiment, both bunk management systems were intended to restrict the magnitude of day-to-day variation in feed delivery.
      Other studies have also examined the effects of imposed variation in day-to-day feed delivery.

      Galyean, M. L., K. J. Malcolm-Callis, D. R. Garcia, and G. D. Pulsipher. 1992. Effects of varying the pattern of feed consumption on performance by programmed-fed beef steers. New Mexico Experiment Station, Clayton Livestock Research Center. Progress Report #78. Accessed Feb. 1, 2021. https://aces.nmsu.edu/aes/clayton/progress_reports/Progress_Report_78.pdf.

      delivered steers either a constant daily feed allotment, or varied the amount of feed delivered by 10% daily or weekly. Although no differences in DMI were observed, the ADG of steers whose feed delivery varied daily was less than both those with constant feed delivery and those that varied weekly. Likewise, feed conversion (F:G) was poorest in cattle whose feed delivery varied daily (

      Galyean, M. L., K. J. Malcolm-Callis, D. R. Garcia, and G. D. Pulsipher. 1992. Effects of varying the pattern of feed consumption on performance by programmed-fed beef steers. New Mexico Experiment Station, Clayton Livestock Research Center. Progress Report #78. Accessed Feb. 1, 2021. https://aces.nmsu.edu/aes/clayton/progress_reports/Progress_Report_78.pdf.

      ). Similarly,
      • Cruz G.D.
      • Pereira I.C.
      • Millen D.D.
      • Arrigoni M.D.
      • Martins C.L.
      • Costa C.F.
      Natural dry matter intake fluctuation impacts performance, feeding behavior and rumen morphometrics of feedlot cattle: 10 yr of data assessment..
      conducted a 10-yr assessment of growth performance and feeding behavior of feedlot cattle with high or low daily DMI fluctuation calculated as DMI fluctuation (kg) ÷ previous day’s DMI (kg) × 100. Cattle with low average daily DMI fluctuation (4.79%) had 4.1% greater ADG, 2.9% greater DMI, and 4.2% greater total BW gain than cohorts with high daily DMI fluctuation (6.74%;
      • Cruz G.D.
      • Pereira I.C.
      • Millen D.D.
      • Arrigoni M.D.
      • Martins C.L.
      • Costa C.F.
      Natural dry matter intake fluctuation impacts performance, feeding behavior and rumen morphometrics of feedlot cattle: 10 yr of data assessment..
      ). Nonetheless, other studies have noted no differences in growth performance or digestive function in calf-fed Holsteins with 20% daily feed delivery variation (

      Zinn, R. A. 1994. Influence of fluctuating feed intake on feedlot cattle growth-performance and digestive function. In Proceedings 9th Southwest Nutrition Management Conference. Accessed Aug. 15, 2021. https://animalscience.ucdavis.edu/sites/g/files/dgvnsk446/files/faculty/zinn/pdf/07.pdf.

      ). In the present study, the effects of feed carryover through differing bunk management systems, but consistent day-to-day feed delivery were evaluated and no differences in feedlot growth performance were observed. Our results support the concept that consistent feed delivery is a component to maximizing production, but that feed carryover itself is perhaps less detrimental than believed.
      Final BW was not different among cattle fed differing bulk densities of SFC (P = 0.57). The ADG of steers fed the 425 g/L SFC-based diet was 5.8% greater from d 35 to 105 (P = 0.05) than those fed the 335 g/L SFC-based diet but was not different from d 105 to final or from d 0 to final (P ≥ 0.36). The standard deviation of ADG within pen did not differ (P = 0.37). At all interim periods, DMI of steers fed 425 g/L SFC-based diets was greater (P ≤ 0.05) than those fed 335 g/L SFC-based diets and was 4.3% greater overall (d 0 to final; P < 0.01). Likewise, grams of DMI per kilogram of metabolic body size (

      Kleiber, M. 1961. The Fire of Life. An Introduction to Animal Energetics. John Wiley and Sons Inc.

      ) was 4.1% greater in steers consuming 425 g/L SFC-based diets. Gain:feed of steers fed 425 g/L SFC-based diets tended (P = 0.10) to be 5.7% lesser from d 0 to 35 than those consuming 335 g/L SFC-based diets, but was not different from d 35 to 105, 105 to final, or 0 to final (P ≥ 0.12). Gain energy density (GED) was not different (P = 0.53). On a carcass-adjusted basis, no differences in final BW, overall ADG, or G:F were observed (P ≥ 0.22). As anticipated, both the performance-adjusted net energy (paNE) and the observed/expected NE was greater (P < 0.01) in 335 g/L SFC-based diets than 425 g/L SFC-based diets. This observation was validated by greater total starch and enzymatically available starch in 335 g/L SFC than 425 g/L SFC. The overall NEg advantage in both diets of the present study compared with tabular values is likely a result of feeding both low-risk, single-source cattle, and the combination of high-quality mid-bloom alfalfa hay and added yellow grease in the diet.
      Processing corn via steam flaking is critical in mitigating the cost of freight, specifically in the southern High Plains of the United States. Steam flaking improves rate and extent of starch digestion via a combination of moist heat and physical shear of starch granules, therefore creating greater surface area for microbial digestion (
      • Zinn R.A.
      • Owens F.N.
      • Ware R.A.
      Flaking corn: Processing mechanics, quality standards, and impacts on energy availability and performance of feedlot cattle..
      ). In addition, heat applied to corn grain results in gelatinization, the irreversible swelling of starch granules, which improves starch solubility (
      • Zinn R.A.
      • Owens F.N.
      • Ware R.A.
      Flaking corn: Processing mechanics, quality standards, and impacts on energy availability and performance of feedlot cattle..
      ). As corn is steam-flaked to a greater degree of processing, bulk density is lighter. In the present study, 335 g/L SFC had greater total starch and enzymatic starch availability than 425 g/L SFC. In comparison,
      • Hales K.E.
      • McMeniman J.P.
      • Leibovich J.
      • Vasconcelos J.T.
      • Quinn M.J.
      • May M.L.
      • DiLorenzo N.
      • Smith D.R.
      • Galyean M.L.
      Effects of varying bulk densities of steam-flaked corn and dietary roughage concentration on in vitro fermentation, performance, carcass quality, and acid-base balance measurements in finishing steers..
      reported total starch of 72.9% and enzymatic starch availability of 67.3% in corn steam-flaked to 335 g/L (26 lb/bu), and total starch of 73.7% and enzymatic starch availability of 63.4% in corn steam-flaked to 386 g/L (30 lb/bu) using the same facilities as the present study. Likewise,
      • Hales K.E.
      • Cole N.A.
      • Galyean M.L.
      • Leytem A.B.
      Nutrient concentrations and proportions in particle size fractions of corn steam flaked to different bulk densities..
      reported the total starch content of intact SFC to be 76.61%, and 74.23% in 335 g/L (26 lb/bu) or 386 g/L (30 lb/bu) flake, respectively.
      Greater DMI in cattle fed 425 g/L SFC-based diets was anticipated because DMI decreases in response to greater dietary energy density (335 g/L) via chemostatic intake regulation and increased metabolic acid concentration (
      • Krehbiel C.R.
      • Cranston J.J.
      • McCurdy M.P.
      An upper limit for caloric density of finishing diets..
      ), as was observed when cattle were fed 335 g/L SFC in the present study. Likewise,
      • Garrett W.N.
      • Johnson D.E.
      Nutritional energetics of ruminants..
      described concentration of ruminal acetate as the primary regulator of short-term DMI when dietary ME is above maintenance. In the present study, paNE and observed/expected NE of 425 g/L SFC diets was indeed lesser than that of 335 g/L SFC diets, supporting the observed increase in DMI when cattle eat to a constant energy. Generally, feedlot nutritionists prefer a medium bulk density (280 to 370 g/L; i.e., 23 to 29 lb/bu) over heavier bulk density counterparts to maximize the NEg value of corn, and to avoid decreased DMI and digestive disfunction often observed in lighter bulk densities (
      • Zinn R.A.
      Influence of flake density on the comparative feeding value of steam-flaked corn for feedlot cattle..
      ;
      • Owens F.N.
      • Secrist D.S.
      • Hill W.J.
      • Gill D.R.
      The effect of grain source and grain processing on performance of feedlot cattle: A review..
      ;
      • Swingle R.S.
      • Eck T.P.
      • Theurer C.B.
      • De la Llata M.
      • Poore M.H.
      • Moore J.A.
      Flake density of steam-processed sorghum grain alters performance and sites of digestibility by growing-finishing steers..
      ). Accordingly, steam flaking was the primary grain processing method in finishing diets in multiple consecutive feedlot nutritionist surveys (
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      ;

      Galyean, M. L., and J. F. Gleghorn. 2001. Summary of the 2000 Texas Tech University Consulting Nutritionist Survey. Texas Tech University Burnett Center Progress Report No. 12. Accessed Jul. 27, 2021. https://www.depts.ttu.edu/afs/burnett_center/progress_reports/bc12.pdf.

      ;
      • Vasconcelos J.T.
      • Galyean M.L.
      Nutritional recommendations of feedlot consulting nutritionists: The 2007 Texas Tech University survey..
      ;
      • Samuelson K.L.
      • Hubbert M.E.
      • Galyean M.L.
      • Löest C.A.
      Nutritional recommendations of feedlot consulting nutritionists: The 2015 New Mexico State and Texas Tech University survey..
      ). In the present study, final BW and overall ADG and G:F of cattle fed 425 g/L SFC-based diets did not differ from cattle fed 335 g/L diets. Likely, the magnitude of greater DMI in cattle fed 425 g/L SFC-based diets compensated for potential losses in NEg value of SFC processed to a lesser degree. Specifically, the cattle fed 425 g/L SFC-based diets consumed 4.3% more DMI, yet the difference in paNEg was 3.2% greater in cattle fed diets 335 g/L SFC-based diets.
      Differing growth performance results have been observed in previous corn processing studies using the same facilities as the present study.
      • Hales K.E.
      • McMeniman J.P.
      • Leibovich J.
      • Vasconcelos J.T.
      • Quinn M.J.
      • May M.L.
      • DiLorenzo N.
      • Smith D.R.
      • Galyean M.L.
      Effects of varying bulk densities of steam-flaked corn and dietary roughage concentration on in vitro fermentation, performance, carcass quality, and acid-base balance measurements in finishing steers..
      evaluated the effect of diets containing 335 g/L (26 lb/bu) or 386 g/L SFC (30 lb/bu) and 6% or 10% dietary roughage concentration. No differences were observed in ADG or DMI; however, overall G:F was lesser in cattle fed 386 g/L SFC. On a carcass-adjusted basis, G:F was not different (
      • Hales K.E.
      • McMeniman J.P.
      • Leibovich J.
      • Vasconcelos J.T.
      • Quinn M.J.
      • May M.L.
      • DiLorenzo N.
      • Smith D.R.
      • Galyean M.L.
      Effects of varying bulk densities of steam-flaked corn and dietary roughage concentration on in vitro fermentation, performance, carcass quality, and acid-base balance measurements in finishing steers..
      ).
      • Ponce C.H.
      • Domby E.M.
      • Anele U.Y.
      • Schutz J.S.
      • Gautam K.K.
      • Galyean M.L.
      Effects of bulk density of steam-flaked corn in diets containing wet corn gluten feed on feedlot cattle performance, carcass characteristics, apparent total tract digestibility, and ruminal fermentation..
      fed diets containing 25% wet corn gluten feed in combination with 283 g/L (22 lb/bu), 335 g/L (26 lb/bu), or 386 g/L (30 lb/bu) SFC and did not observe any differences in feedlot growth performance on both a live- and carcass-adjusted basis. Nonetheless, although not statistically significant, numerical trends were observed for overall DMI and carcass-adjusted ADG and G:F to increase with increasing bulk density (
      • Ponce C.H.
      • Domby E.M.
      • Anele U.Y.
      • Schutz J.S.
      • Gautam K.K.
      • Galyean M.L.
      Effects of bulk density of steam-flaked corn in diets containing wet corn gluten feed on feedlot cattle performance, carcass characteristics, apparent total tract digestibility, and ruminal fermentation..
      ).
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      fed 283 g/L or 360 g/L SFC (22 lb/bu or 28 lb/bu, respectively) in combination with differing dietary concentrations of wet corn gluten feed and roughage. No differences of bulk density were observed in ADG, DMI, or G:F on a live weight basis, but carcass-adjusted G:F was greater in cattle fed 360 g/L SFC (
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      ). The ADG and G:F results of these studies generally support what was observed in the present study. Lack of differences in DMI reported by
      • Ponce C.H.
      • Domby E.M.
      • Anele U.Y.
      • Schutz J.S.
      • Gautam K.K.
      • Galyean M.L.
      Effects of bulk density of steam-flaked corn in diets containing wet corn gluten feed on feedlot cattle performance, carcass characteristics, apparent total tract digestibility, and ruminal fermentation..
      and
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      could be a difference in diet composition, as these studies included corn milling by-products, and the present study did not. Many other studies using SFC and steam-flaked sorghum have reported greater DMI with greater bulk density (
      • Xiong Y.
      • Bartle S.J.
      • Preston R.L.
      Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers..
      ;
      • Reinhardt C.D.
      • Brandt Jr., R.T.
      • Behnke K.C.
      • Freeman A.S.
      • Eck T.P.
      Effect of steam-flaked sorghum grain density on performance, mill production rate, and subacute acidosis in feedlot steers..
      ;
      • Swingle R.S.
      • Eck T.P.
      • Theurer C.B.
      • De la Llata M.
      • Poore M.H.
      • Moore J.A.
      Flake density of steam-processed sorghum grain alters performance and sites of digestibility by growing-finishing steers..
      ;
      • Theurer C.B.
      • Lozano O.
      • Alio A.
      • Delgado-Elorduy A.
      • Sadik M.
      • Huber J.T.
      • Zinn R.A.
      Steam-processed corn and sorghum grain flaked at different densities alter ruminal, small intestinal, and total tract digestibility of starch by steers..
      ;
      • Zinn R.A.
      • Barreras A.
      • Owens F.N.
      • Plascencia A.
      Performance by feedlot steers and heifers: daily gain, mature body weight, dry matter intake, and dietary energetics..
      ).

      Carcass Characteristics

      No differences in hot carcass weight were observed for the main effects of bunk management (P ≥ 0.67; Table 5). Additionally, continuous carcass variables were not affected by bunk management (P ≥ 0.34).
      • Old C.A.
      • Garrett W.N.
      Effects of energy intake on energetic efficiency and body composition of beef steers differing in size at maturity..
      reported that percentage water, fat, protein, and Mcal/kg of the empty body did not differ among cattle fed ad libitum, or 70% or 85% of ad libitum intake. When expressed as a percentage of gain, cattle fed 70% of ad libitum had more water, less fat, and more protein than those fed to ad libitum intake or 85% of ad libitum (
      • Old C.A.
      • Garrett W.N.
      Effects of energy intake on energetic efficiency and body composition of beef steers differing in size at maturity..
      ). In carcasses adjusted to an equivalent hot carcass weight,
      • Preston R.L.
      • Vance R.D.
      • Cahill V.R.
      Energy evaluation of brewers grains for growing and finishing cattle..
      observed greater carcass adiposity in cattle fed ad libitum intake than those fed 80% of ad libitum by measure of marbling score, fat thickness, empty body fat percentage (EBF), and percentage KPH. Likewise,
      • Delfino J.G.
      • Mathison G.W.
      Effects of cold environment and intake level on the energetic efficiency of feedlot steers..
      reported hot carcass weight and DP to be greater with increasing feeding level (52, 64, or 70 g of DM/kg of BW0.75). When the data of
      • Preston R.L.
      • Vance R.D.
      • Cahill V.R.
      Energy evaluation of brewers grains for growing and finishing cattle..
      ,
      • Old C.A.
      • Garrett W.N.
      Effects of energy intake on energetic efficiency and body composition of beef steers differing in size at maturity..
      , and
      • Delfino J.G.
      • Mathison G.W.
      Effects of cold environment and intake level on the energetic efficiency of feedlot steers..
      were summarized in a meta-analysis by
      • Owens F.N.
      • Gill D.R.
      • Secrist D.S.
      • Coleman S.
      Review of some aspects of growth and development of feedlot cattle..
      , carcass composition did not differ, which is in agreement with the main effect of bunk management in the present study. Additionally, compared with that of the present study, DMI was more restrictive in the studies of
      • Preston R.L.
      • Vance R.D.
      • Cahill V.R.
      Energy evaluation of brewers grains for growing and finishing cattle..
      ,
      • Old C.A.
      • Garrett W.N.
      Effects of energy intake on energetic efficiency and body composition of beef steers differing in size at maturity..
      , and
      • Delfino J.G.
      • Mathison G.W.
      Effects of cold environment and intake level on the energetic efficiency of feedlot steers..
      , which ranged from 85% of ad libitum DMI as the least restrictive and 70% of ad libitum DMI as the most restrictive. By comparison, slick-bunk management and other programmed feeding systems apply lesser DMI restrictions of 5 to 10% less than expected ad libitum DMI (
      • Pritchard R.H.
      • Bruns K.W.
      Controlling variation in feed intake through bunk management..
      ), which further supports the lack of carcass differences between slick and modified ad libitum bunk management in the present study.
      Table 5Main effects of bunk management and bulk density of steam-flaked corn on carcass characteristics of finishing beef steers
      Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.33).
      ItemBunk managementP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      Flake densityP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      SEM
      Pooled SE of LSM (n = 24 pens/mean).
      ALS335 g/L425 g/L
      Hot carcass weight, kg4034000.673994040.384.2
      DP,
      Calculated as hot carcass weight divided by final shrunk BW.
      %
      66.1466.070.7765.9366.280.150.207
      Marbling score
      Leading digit in marbling indicates score; 2 = trace, 3 = slight, 4 = small, 5 = modest, 6 = moderate, 7 = slightly abundant, 8 = moderately abundant, 9 = abundant. The following digits indicate degree of marbling within marbling score.
      5075150.655025200.2913.3
      Fat thickness, cm1.661.680.761.591.750.070.065
      Longissimus dorsi area, cm
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      94.8893.590.3494.9893.490.271.053
      Calculated YG3.303.370.603.203.470.050.097
      EBF,
      Empty body fat, %. Estimated using equations of Guiroy et al. (2001).
      %
      31.1031.320.6930.6731.760.060.428
      AFBW,
      Adjusted final shrunk weight at 28% EBF estimated using equations of Tylutki et al. (1994).
      kg
      5425340.505485290.099.1
      1 Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.33).
      2 Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      3 Pooled SE of LSM (n = 24 pens/mean).
      4 Calculated as hot carcass weight divided by final shrunk BW.
      5 Leading digit in marbling indicates score; 2 = trace, 3 = slight, 4 = small, 5 = modest, 6 = moderate, 7 = slightly abundant, 8 = moderately abundant, 9 = abundant. The following digits indicate degree of marbling within marbling score.
      6 Empty body fat, %. Estimated using equations of
      • Guiroy P.J.
      • Fox D.G.
      • Tedeschi L.O.
      • Baker M.J.
      • Cravey M.D.
      Predicting individual feed requirements of cattle fed in groups..
      .
      7 Adjusted final shrunk weight at 28% EBF estimated using equations of
      • Tylutki T.P.
      • Fox D.G.
      • Anrique R.G.
      Predicting net energy and protein requirements for growth of implanted and nonimplanted heifers and steers and nonimplanted bulls varying in body size..
      .
      Hot carcass weight, DP, marbling score, and Longissimus dorsi area did not differ between steers fed 335 g/L SFC and 425 g/L SFC (P ≥ 0.15). Fat thickness (P = 0.07) and calculated EBF (P = 0.06) tended to be greater in steers fed 425 g/L SFC-based diets. Similarly, the calculated YG of steers fed 425 g/L SFC-based diets was greater than those fed 335 g/L SFC-based diets. The final BW adjusted to 28% EBF tended to be 3.5% lesser in steers fed 425 g/L SFC (P = 0.09).
      Percentage USDA Prime, Choice, or Select QG were not affected (Table 6; P ≥ 0.51) by bunk management or bulk density of SFC. There was a tendency (P = 0.10) for steers on slick-bunk management to have greater percentage of YG 1 carcasses, but a biological reason for this tendency is unclear given that no other differences in carcass composition or live growth performance was observed. Cattle fed 425 g/L SFC-based diets had a lesser incidence of YG 3 carcasses (P = 0.02), and a greater incidence of YG 4 or 5 carcasses (P < 0.01).
      Table 6Main effects of bunk management and bulk density of steam-flaked corn on categorical carcass characteristics of finishing beef steers
      Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.09).
      ItemBunk managementP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      Flake densityP-value
      Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      SEM
      Pooled SE of LSM (n = 24 pens/mean).
      ALS335 g/L425 g/L
      QG, %
       Prime5.566.600.784.867.290.512.597
       Choice82.9981.600.7982.6481.940.903.694
       Select11.4611.810.9312.5010.760.683.605
      YG, %
       17.2913.540.1010.7610.070.853.126
       228.4719.100.1324.3123.260.874.309
       346.5342.710.5552.0837.150.026.071
       4 or 517.7124.650.1912.8529.51<0.013.670
      Liver score, %
       Abscessed24.3127.880.6929.5116.670.044.205
       A
      A = 2 to 4 small active abscesses (<6 cm in diameter); minor abscesses.
      19.1016.670.6622.2213.540.123.820
       A+
      A+ = 1 or more large (>6 cm in diameter), active abscesses; severe abscesses.
      5.215.211.007.293.130.252.532
      1 Bunk management methods were modified ad libitum (AL; target up to 5% orts at 0730 h bunk read) or slick (S; target trace or slick at 0730 h bunk read). Bulk density of steam-flaked corn was 335 g/L (26 lb/bu) or 425 g/L (33 lb/bu). No interaction of bunk management × bulk density of steam-flaked corn was observed (P ≥ 0.09).
      2 Observed significance level for main-effect comparison of bunk management or bulk density of steam-flaked corn.
      3 Pooled SE of LSM (n = 24 pens/mean).
      4 A = 2 to 4 small active abscesses (<6 cm in diameter); minor abscesses.
      5 A+ = 1 or more large (>6 cm in diameter), active abscesses; severe abscesses.
      Adipose is an energetically efficient tissue and accretes at approximately 1.6 times the rate of protein on a caloric basis, and on a wet-tissue basis, protein accretion requires fewer kilocalories than adipose accretion (1.2 vs. 8.3 kcal/g, respectively;
      • Owens F.N.
      • Gill D.R.
      • Secrist D.S.
      • Coleman S.
      Review of some aspects of growth and development of feedlot cattle..
      ). Therefore, taking into consideration the water stored within protein, lean tissue gain is 4 times more efficient than adipose tissue gain (
      • Owens F.N.
      • Gill D.R.
      • Secrist D.S.
      • Coleman S.
      Review of some aspects of growth and development of feedlot cattle..
      ). Nonetheless, adipose becomes a greater proportion of tissue gain with advanced maturity (

      Simpfendorfer, S. 1974. Relationship of Body Type, Size, Sex, and Energy Intake to the Body Composition of Cattle. PhD Dissertation. Cornell University, Ithaca, NY.

      ;

      NASEM. 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ). Concomitantly, GED increases with advanced maturity, which leads to greater EBF% at harvest (
      • Gentry W.W.
      • Blom E.J.
      • Pritchard R.H.
      • Hales K.E.
      Effect of anabolic hormone exposure during the backgrounding-phase in calf-fed steers of different mature sizes..
      ). In the present study, cattle consuming 425 g/L SFC had greater carcass 12th rib fat thickness than 335 g/L SFC-fed cattle, had greater incidence of YG 4 and 5, and a tendency for greater calculated EBF% despite no differences observed in G:F or GED. Likewise, no difference in final BW were observed on both a live- and carcass-adjusted basis, but when final BW was adjusted to equivalent 28% EBF, steers fed 335 g/L SFC were heavier.
      Greater carcass adiposity in cattle consuming the lesser processed SFC was likely a result of greater DMI and throughout the feeding period. Cattle fed the 425 g/L SFC-based diets consumed approximately 4.3% more Mcal of NEg per animal daily than their counterparts fed 335 g/L SFC-fed cattle, which is consistent with a decreased net energy value for SFC processed to 425 g/L SFC. Greater carcass adiposity and lean yield in cattle consuming a lesser processed grain has been frequently, but not consistently reported by a variety of measurements, including greater hot carcass weight (
      • Reinhardt C.D.
      • Brandt Jr., R.T.
      • Behnke K.C.
      • Freeman A.S.
      • Eck T.P.
      Effect of steam-flaked sorghum grain density on performance, mill production rate, and subacute acidosis in feedlot steers..
      ;
      • Swingle R.S.
      • Eck T.P.
      • Theurer C.B.
      • De la Llata M.
      • Poore M.H.
      • Moore J.A.
      Flake density of steam-processed sorghum grain alters performance and sites of digestibility by growing-finishing steers..
      ;
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      ), DP (
      • Reinhardt C.D.
      • Brandt Jr., R.T.
      • Behnke K.C.
      • Freeman A.S.
      • Eck T.P.
      Effect of steam-flaked sorghum grain density on performance, mill production rate, and subacute acidosis in feedlot steers..
      ;
      • Ponce C.H.
      • Domby E.M.
      • Anele U.Y.
      • Schutz J.S.
      • Gautam K.K.
      • Galyean M.L.
      Effects of bulk density of steam-flaked corn in diets containing wet corn gluten feed on feedlot cattle performance, carcass characteristics, apparent total tract digestibility, and ruminal fermentation..
      ;
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      ), increase in percentage of Choice carcasses (
      • Xiong Y.
      • Bartle S.J.
      • Preston R.L.
      Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers..
      ;
      • Hales K.E.
      • McMeniman J.P.
      • Leibovich J.
      • Vasconcelos J.T.
      • Quinn M.J.
      • May M.L.
      • DiLorenzo N.
      • Smith D.R.
      • Galyean M.L.
      Effects of varying bulk densities of steam-flaked corn and dietary roughage concentration on in vitro fermentation, performance, carcass quality, and acid-base balance measurements in finishing steers..
      ), greater LM area (
      • Ponce C.H.
      • Domby E.M.
      • Anele U.Y.
      • Schutz J.S.
      • Gautam K.K.
      • Galyean M.L.
      Effects of bulk density of steam-flaked corn in diets containing wet corn gluten feed on feedlot cattle performance, carcass characteristics, apparent total tract digestibility, and ruminal fermentation..
      ), and greater fat thickness (
      • Domby E.M.
      • Anele U.Y.
      • Gautam K.K.
      • Hergenreder J.E.
      • Pepper-Yowell A.R.
      • Galyean M.L.
      Interactive effects of bulk density of steam-flaked corn and concentration of Sweet Bran on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility..
      ). These observations are likely caused by greater DMI throughout the feeding period (
      • Xiong Y.
      • Bartle S.J.
      • Preston R.L.
      Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers..
      ;
      • Reinhardt C.D.
      • Brandt Jr., R.T.
      • Behnke K.C.
      • Freeman A.S.
      • Eck T.P.
      Effect of steam-flaked sorghum grain density on performance, mill production rate, and subacute acidosis in feedlot steers..
      ;
      • Swingle R.S.
      • Eck T.P.
      • Theurer C.B.
      • De la Llata M.
      • Poore M.H.
      • Moore J.A.
      Flake density of steam-processed sorghum grain alters performance and sites of digestibility by growing-finishing steers..
      ;
      • Theurer C.B.
      • Lozano O.
      • Alio A.
      • Delgado-Elorduy A.
      • Sadik M.
      • Huber J.T.
      • Zinn R.A.
      Steam-processed corn and sorghum grain flaked at different densities alter ruminal, small intestinal, and total tract digestibility of starch by steers..
      ), which is in agreement with the present study.
      Liver abscess incidence and severity at slaughter were not affected by bunk management strategy (P ≥ 0.66). Steers fed 425 g/L SFC-based diets had 43.51% fewer (P = 0.04) liver abscesses; however, no difference in liver abscess severity was observed (P ≥ 0.12).
      As free glucose is liberated from starch granules in the rumen, lactate-producing microbes, especially Streptococcus bovis, are provided a favorable environment for proliferation and lactic acidosis may develop as a result (
      • Owens F.N.
      • Secrist D.S.
      • Hill W.J.
      • Gill D.R.
      Acidosis in cattle: A review..
      ). Streptococcus bovis are lactate-producing, acid-tolerant ruminal bacteria with rapid doubling time in environments where readily fermentable carbohydrate is available, thus easily dominating the microbial environment and altering the ruminal ecology to a more acidic state (

      Russell, J. B. 2002. Rumen Microbiology and Its Role in Ruminant Nutrition. James B. Russell, Ithaca, NY.

      ). As the severity of lactic acidosis progresses, integrity of the rumen wall may become compromised, allowing rumen microbes to escape, enter hepatic circulation, and become sequestered in the liver. Consequently, a liver abscess is formed (
      • Nagaraja T.G.
      • Chengappa M.M.
      Liver abscesses in feedlot cattle: A review..
      ). Liver abscesses have been known to be a detriment to growth performance and carcass value of beef cattle for several decades (
      • Brown H.
      • Bing R.F.
      • Grueter H.P.
      • McAskill J.W.
      • Cooley C.O.
      • Rathmacher R.P.
      Tylosin and chlortetracycline for the prevention of liver abscesses, improved weight gains and feed efficiency in feedlot cattle..
      ;
      • Brink D.R.
      • Lowry S.R.
      • Stock R.A.
      • Parrott J.C.
      Severity of liver abscesses and efficiency of feed utilization of feedlot cattle..
      ;
      • Reinhardt C.D.
      • Hubbert M.E.
      Control of liver abscesses in feedlot cattle: A review..
      ). In a meta-analysis,
      • Brink D.R.
      • Lowry S.R.
      • Stock R.A.
      • Parrott J.C.
      Severity of liver abscesses and efficiency of feed utilization of feedlot cattle..
      reported cattle with severely abscessed livers had 8.2% less ADG, 6.2% less DMI, 8 kg less final BW, and 4.5% less hot carcass weight compared with cohorts with no liver abscess. Likewise,
      • Brown T.R.
      • Lawrence T.E.
      Association of liver abnormalities with carcass grading performance and value..
      reported hot carcass weight of cattle with A− or A+ livers to be less compared with cohorts with normal livers. In a survey of consulting feedlot nutritionists representing over 14 million cattle on feed annually (approximately 11.1%),
      • Samuelson K.L.
      • Hubbert M.E.
      • Galyean M.L.
      • Löest C.A.
      Nutritional recommendations of feedlot consulting nutritionists: The 2015 New Mexico State and Texas Tech University survey..
      reported medicated feed additives were used by 83.4% of nutritionist’s clients to control liver abscesses. Of the compounds approved for this purpose, tylosin phosphate is considered most effective and therefore is the most widely used (
      • Nagaraja T.G.
      • Sun Y.
      • Wallace N.
      • Kemp K.E.
      • Parrott C.J.
      Effects of tylosin on concentrations of Fusobacterium necrophorum and fermentation products in the rumen of cattle fed a high-concentrate diet..
      ).
      In a national liver audit by

      Herrick, R. T. 2018. Experiments towards a greater understanding of the liver abscess complex in fed beef. Dissertation. West Texas A&M University, Canyon, TX.

      , 130,845 livers from 7 fed beef processing facilities were evaluated. Average liver abscess incidence was 20.3% overall (fed beef steers = 18.2%; fed beef heifers = 19.1%; fed Holsteins = 25.0%). Comparably, in the present study, liver abscess incidence in steers fed 425 g/L SFC-based diets without tylosin phosphate was 16.7%, a notable decrease compared with steers fed 335 g/L SFC-based diets (29.5%). Demonstrated in the present study, a lighter bulk density of SFC has greater enzymatic starch availability, which could serve as a predisposing factor for digestive dysfunction and the development of liver abscesses, especially in diets with decreased NDF from roughage. As the beef industry continues to seek alternatives to antimicrobials, increasing bulk density of SFC from the industry average of 350 g/L (27 lb/bu;
      • Samuelson K.L.
      • Hubbert M.E.
      • Galyean M.L.
      • Löest C.A.
      Nutritional recommendations of feedlot consulting nutritionists: The 2015 New Mexico State and Texas Tech University survey..
      ) could be a management-based alternative to feeding tylosin phosphate; however, more research should be conducted in this area.

      APPLICATIONS

      Bunk management and bulk density of SFC are common feedlot management practices, and more research is needed involving these procedures with diets without tylosin phosphate. In the present study, bunk management did not affect measures of growth performance, carcass characteristics, or liver abscess score and severity. Compared with steers fed diets containing 335 g/L SFC, steers fed 425 g/L SFC-based diets had greater DMI, similar overall feed efficiency, and 43.5% fewer liver abscesses; however, the steers fed 425 g/L SFC-based diets were also fatter according to carcass-based measurements. Increasing bulk density of SFC, thereby decreasing degree of processing, could be a useful management strategy as the beef industry strives to decrease antimicrobial use, but additional research is needed.

      ACKNOWLEDGMENTS

      This study was funded by the Thornton Endowment in Animal Science at Texas Tech University (Lubbock, TX). The authors thank Fiver Rivers Cattle Feeding (Johnstown, CO) for supplying cattle for this research; W. Nichols and J. Hutcheson (Merck Animal Health, Madison, NJ) for their donation of vaccines and implants; B. Bernhard (Zoetis, Florham Park, NJ) for their donation of dewormer; G. Vogel (Elanco Animal Health, Greenfield, IN) for their donation of monensin; P. W. Rounds (Kemin Industries, Des Moines, IA) for their donation of grain surfactant; DSM Animal Nutrition and Health (Parsippany, NJ) for their donation of vitamin E; B. Wasson (Servi-Tech Laboratories, Dodge City, KS), R. Cox (Servi-Tech Laboratories, Amarillo, TX), and A. Krieg (Texas Tech University) for their assistance in developing the starch availability assay; and K. Robinson and R. Rocha (Texas Tech University Burnett Center, Idalou, TX) for their technical assistance.

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