Advertisement

Effects of changes in finishing diets and growth technologies on animal growth performance and the carbon footprint of cattle feeding: 1990 to 2020

      ABSTRACT

      Objective

      Our objective was to estimate the effects of changes in feedlot diets and the availability of performance-enhancing technologies on growth performance and the carbon footprint of cattle feeding between 1990 and 2020.

      Materials and Methods

      A model was developed to represent feedlot diets and technologies used in 1990 versus 2020 and evaluate changes in growth performance and carbon footprint. Byproduct feeds became more common between 1990 and 2020; thus, corn and dry roughage inclusion rates decreased. Estradiol-only implants and monensin were the available technologies in 1990, whereas in 2020 use of implants with combinations of trenbolone acetate and estradiol, monensin, and ractopamine hydrochloride (in the final 28 to 42 d) were common.

      Results and Discussion

      In both 1990 and 2020 use of all available technologies increased final BW, ADG, G:F, and hot carcass weight compared with no technology. From 1990 to 2020 initial BW, final BW, ADG, G:F, hot carcass weight, and daily DMI increased. Total days on feed increased by 44 d from 1990 to 2020. Compared with no technology, use of technologies in both 1990 and 2020 decreased total greenhouse gas emissions per animal (CO2 equivalent, CO2e). Because cattle had greater days on feed in 2020, all sources of greenhouse gas emissions per animal increased compared with the values estimated in 1990. However, when expressed as CO2e/kg of BW gain, emissions have decreased by 4.4% because of greater total BW gain in 2020 versus 1990.

      Implications and Applications

      Feedlot cattle decreased relative emissions from 4.78 kg of CO2e/kg of BW gain in 1990 to 4.58 kg of CO2e/kg of BW gain in 2020. Overall, feedlots in 2020 produced 47.5% more BW gain with 1.4% less cattle, while only increasing total CO2e by 39.5%. Therefore, changes in available technologies and diet formulations have improved efficiency and reduced the carbon footprint of feedlot cattle production in the past 30 yr.

      Key words

      INTRODUCTION

      As the global population grows and demand for beef increases, management practices must evolve to accommodate changes in feedstuff availability, enhance growth efficiency, and address consumer concerns regarding the environmental sustainability of livestock production. To facilitate these enhancements, research has focused on developing technologies and animal management techniques to improve growth performance and accommodate the needs of an ever-changing beef industry. For example, between 1990 and 2020 there have been distinct changes in feedlot cattle diets and an increase in the availability and use of growth-promoting technologies. Grain-milling byproducts such as corn gluten feed and distillers grains have become common ingredients in feedlot cattle diets (
      • 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..
      ), yet these ingredients were scarcely available in 1990. Availability and use of growth-promoting technologies such as implants, ionophores, and β-adrenergic agonists (βAA) have also changed significantly over the past 30 yr as research has been conducted to refine the management practices surrounding their administration and develop new products.
      Consumers are continually expressing greater concern for the effect that beef cattle production has on the environment and how this may affect sustainability of the beef production system. Methane (CH4), CO2, and N2O are greenhouse gases emitted as waste products from inefficiencies of ruminal fermentation, as metabolic byproducts, and from degradation of manure. Calculating a carbon footprint (C-footprint) adjusts each of the greenhouse gases to a common CO2 equivalent (CO2e) to represent the total potential for global warming (GWP).
      Changes in diets and the use of growth-promoting technologies have improved growth performance of beef cattle compared with natural beef production systems (
      • Wileman B.W.
      • Thomson D.U.
      • Reinhardt C.D.
      • Renter D.G.
      Analysis of modern technologies commonly used in beef cattle production: Conventional beef production versus nonconventional production using meta-analysis..
      ). In addition, these improvements in growth performance have increased feed efficiency and reduced the environmental impact of raising cattle in feedlots (
      • Stackhouse-Lawson K.R.
      • Calvo M.S.
      • Place S.E.
      • Armitage T.L.
      • Pan Y.
      • Zhao Y.
      • Mitloehner F.M.
      Growth promoting technologies reduce greenhouse gas, alcohol, and ammonia emissions from feedlot cattle..
      ). Our objective was to estimate the effects of current feedlot diets and technologies on animal growth performance and the C-footprint of cattle feeding between 1990 and 2020.

      MATERIALS AND METHODS

      Because no live animals were used, this research was not evaluated by the Institutional Animal Care and Use Committee at West Texas A&M University. For this study, a model was developed to represent typical feedlot finishing diets (Table 1) fed to cattle in 1990 and 2020 using dietary ingredients that had a C-footprint reported in the literature (
      • Adom F.
      • Maes A.
      • Workman C.
      • Clayton-Nierderman Z.
      • Thoma G.
      • Shonnard D.
      Regional carbon footprint analysis of dairy feeds for milk production in the USA..
      ). The diets contained steam-flaked corn, alfalfa hay, soybean meal, tallow, and supplement in 1990, and in 2020 wet distillers grains plus solubles (WDGS) replaced a portion of steam-flaked corn and all of soybean meal. Steam flaking was used in both years because it was the most widely used processing method for corn according to
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      and
      • 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..
      . The 20.0% of dietary DM inclusion of WDGS in the 2020 diet was selected based on the most recent consulting nutritionist survey conducted in 2015 (
      • 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..
      ). Technologies reported in the 1990 model included no technology, growth-promoting implants (estrogen only), ionophores, and the use of both implants and an ionophore in combination. In contrast, the 2020 model included no technology; implants (estrogen and androgen combination); ionophores; implants and ionophores in combination; βAA; and the combination of implants, ionophores, and βAA. Ractopamine hydrochloride (RH) was used to model the performance improvements associated with βAA administration because it was the only βAA used in the United States in 2020. Monensin sodium was selected to describe the effects of ionophores in both 1990 and 2020 because it was reported to be the most widely used ionophore in feedlot cattle diets (
      • Russell J.B.
      • Strobel H.J.
      Effect of ionophores on ruminal fermentation..
      ;
      • 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..
      ). Although not every possible combination of technologies is presented, those reported in the model represent commonly used technologies in the feedlot industry in the last 30 yr.
      Table 1Ingredient and nutrient composition of typical feedlot finishing diets fed in 1990 and 2020
      Item1990 Diet2020 Diet
      Ingredient, % of DM
       Steam-flaked corn76.465.4
       Alfalfa hay, mature13.09.0
       Wet distillers grains plus solubles20.0
       Soybean meal5.0
       Tallow2.52.5
       Supplement3.13.1
      Tabular nutrient estimate, DM basis
       CP, %12.5015.42
       Fat, %5.176.87
       Starch, %66.6751.35
       NDF, %14.9615.93
       Calcium, %0.640.82
       Phosphorus, %0.250.35
       NEm,
      Based on tabular values reported by NASEM (2016).
      Mcal/kg
      2.222.34
       NEg,
      Based on tabular values reported by NASEM (2016).
      Mcal/kg
      1.531.63
      1 Based on tabular values reported by

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      .
      For the 1990 model, a review of feedlot cattle studies published in theJournal of Animal Science between 1990 and 1995 and closeout records from the 1997 Kansas State University Focus on Feedlots Reports (

      Kuhl, G. 1997. Kansas State University Focus on Feedlots. Accessed Sep. 18, 2021. https://www.asi.k-state.edu/about/newsletters/focus-on-feedlots/monthly-reports.html.

      ) were conducted to establish values for comparison of growth performance under different management conditions. Manuscripts were excluded if they contained treatments that used programed feeding, where cattle were fed to achieve a certain ADG and thereforead libitum intake was not achieved. In addition, manuscripts that did not contain growth performance measurements were excluded. The 1997 Kansas State University Focus on Feedlots Reports were used because they represented the earliest publicly available date for cattle fed in the 1990s. A total of 9 publications and 3 Kansas Focus on Feedlots Reports were used in a weighted average to calculate initial and final BW and ADG from the selected study treatment means (
      • Lewis J.M.
      • Klopfenstein T.J.
      • Stock R.A.
      Effects of rate of gain during winter on subsequent grazing and finishing performance..
      ;
      • Zinn R.A.
      Influence of flake density on the comparative feeding value of steam-flaked corn for feedlot cattle..
      ;
      • Xiong Y.
      • Bartle S.J.
      • Preston R.L.
      Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers..
      ;
      • Zinn R.A.
      Comparative feeding value of steam-flaked corn and sorghum in finishing diets supplemented with or without sodium bicarbonate..
      ;
      • Ham G.A.
      • Stock R.A.
      • Klopfenstein T.J.
      • Larson E.M.
      • Shain D.H.
      • Huffman R.P.
      Wet corn distillers byproducts compared with dried corn distillers grains with solubles as a source of protein and energy for ruminants..
      ;
      • Bauer M.L.
      • Herold D.W.
      • Britton R.A.
      • Stock R.A.
      • Klopfenstein T.J.
      • Yates D.A.
      Efficacy of laidlomycin propionate to reduce ruminal acidosis in cattle..
      ;
      • Krehbiel C.R.
      • Stock R.A.
      • Shain D.H.
      • Richards C.J.
      • Ham G.A.
      • McCoy R.A.
      • Klopfenstein T.J.
      • Britton R.A.
      • Huffman R.P.
      Effect of level and type of fat on subacute acidosis in cattle fed dry-rolled corn finishing diets..
      ;
      • Ladely S.R.
      • Stock R.A.
      • Goedeken F.K.
      • Huffman R.P.
      Effect of corn hybrid and grain processing method on rate of starch disappearance and performance of finishing cattle..
      ;
      • Ludden P.A.
      • Cecava M.J.
      • Hendrix K.S.
      The value of soybean hulls as a replacement for corn in beef cattle diets formulated with or without added fat..
      ). Baseline DMI was determined using the DMI prediction equation proposed by the

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      , DMI = 4.54 + 0.0125 × initial BW). Gain-to-feed ratio was calculated by dividing the ADG by DMI. These values were used to model baseline growth performance for cattle receiving both an implant and monensin. Performance (final BW and ADG) for cattle receiving an implant only, monensin only, and no technology (no implant, no monensin) was then back-calculated by removing the improvements in performance associated with each technology from the baseline.
      Initial BW was not adjusted based on the different technologies used. However, final BW was reduced by 35 kg when implants were not used (no technology and monensin only) in accordance with the

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      . The DMI was decreased by 6% for the non-use of implants (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      ) and increased by 4% when monensin was not included in the diet (
      • Galyean M.L.
      • Malcolm K.J.
      • Duff G.C.
      Performance of feedlot steers fed diets containing laidlomycin propionate or monensin plus tylosin, and effects of laidlomycin propionate concentration on intake patterns and ruminal fermentation in beef steers during adaptation to a high-concentrate diet..
      ). The ADG was decreased by 1.5% for cattle that did not receive monensin (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      ) and 17.0% (
      • Duckett S.K.
      • Andrae J.G.
      Implant strategies in an integrated beef production system..
      ) for cattle that did not receive estrogenic implants. The performance changes associated with estrogenic implants were chosen from
      • Duckett S.K.
      • Andrae J.G.
      Implant strategies in an integrated beef production system..
      because they represented the available technology in 1990, as use of an implant containing estrogen only was a common management practice during this time. The effects of both monensin and implant on DMI and ADG were assumed to be additive. The total number of days on feed (DOF) was calculated for each group by dividing the total BW gain by the ADG and is similar to the selected reference studies. Dressing percentage for the all technology group was set at 63.0% of final BW (personal communication, Ty Lawrence, West Texas A&M University, Canyon, TX). In the groups that did not receive an estrogenic implant, DP was increased by 0.16% points (
      • Reinhardt C.D.
      • Wagner J.J.
      High-dose anabolic implants are not all the same for growth and carcass traits of feedlot steers: A meta-analysis..
      ). Hot carcass weight was calculated by multiplying the DP by the final BW.
      To model growth performance of cattle fed in 2020, baseline values were determined using a literature search of feedlot research published in theJournal of Animal Science between 2015 and 2020 and monthly closeout reports from the 2020 Kansas Focus on Feedlots (

      Waggoner, J. 2020. Kansas State University Focus on Feedlots. Accessed Sep. 18, 2021. https://www.asi.k-state.edu/about/newsletters/focus-on-feedlots/monthly-reports.html.

      ). Manuscripts were eliminated from the data pool if monensin, a combination implant, or RH was not used. A total of 10 journal articles were used (
      • Russell J.R.
      • Lundy E.L.
      • Minton N.O.
      • Sexten W.J.
      • Kerley M.S.
      • Hansen S.L.
      Influence of growing phase feed efficiency classification on finishing phase growth performance and carcass characteristics of beef steers fed different diet types..
      ;
      • Schwandt E.F.
      • Wagner J.J.
      • Engle T.E.
      • Bartle S.J.
      • Thomson D.U.
      • Reinhardt C.D.
      The effects of dry-rolled corn particle size on performance, carcass traits, and starch digestibility in feedlot finishing diets containing wet distiller’s grains..
      ;
      • Stokes R.S.
      • Loy D.D.
      • Hansen S.L.
      Effects of increased inclusion of algae meal on finishing steer performance and carcass characteristics..
      ;
      • Thompson A.J.
      • Smith Z.K.F.
      • Corbin M.J.
      • Harper L.B.
      • Johnson B.J.
      Ionophore strategy affects growth performance and carcass characteristics in feedlot steers..
      ;
      • Genther-Schroeder O.N.
      • Branine M.E.
      • Hansen S.L.
      Effects of increasing supplemental dietary Zn concentration on growth performance and carcass characteristics in finishing steers fed ractopamine hydrochloride..
      ;
      • Müller H.C.
      • Van Bibber-Krueger C.L.
      • Ogunrinu O.J.
      • Amachawadi R.G.
      • Scott H.M.
      • Drouillard J.S.
      Effects of intermittent feeding of tylosin phosphate during the finishing period on feedlot performance, carcass characteristics, antimicrobial resistance, and incidence and severity of liver abscesses in steers..
      ;
      • Budde A.M.
      • Sellins K.
      • Lloyd K.E.
      • Wagner J.J.
      • Heldt J.S.
      • Spears J.W.
      • Engle T.E.
      Effect of zinc source and concentration and chromium supplementation on performance and carcass characteristics in feedlot steers..
      ;
      • Teixeira P.D.
      • Tekippe J.A.
      • Rodrigues L.M.
      • Ladeira M.M.
      • Pukrop J.R.
      • Kim Y.H.B.
      • Schoonmaker J.P.
      Effect of ruminally protected arginine and lysine supplementation on serum amino acids, performance, and carcass traits of feedlot steers..
      ;
      • Warner A.L.
      • Beck P.A.
      • Foote A.P.
      • Pierce K.N.
      • Robison C.A.
      • Hubbell D.S.
      • Wilson B.K.
      Effects of utilizing cotton byproducts in a finishing diet on beef cattle performance, carcass traits, fecal characteristics, and plasma metabolites..
      ;
      • Wellmann K.B.
      • Baggerman J.O.
      • Burson W.C.
      • Smith Z.K.
      • Kim J.
      • Hergenreder J.E.
      • Rounds W.
      • Bernhard B.C.
      • Johnson B.J.
      Effects of zinc propionate supplementation on growth performance, skeletal muscle fiber, and receptor characteristics in beef steers..
      ), and a weighted average between the journal articles and the Kansas reports was used for initial BW, final BW, and ADG. Dry matter intake was calculated using the equation DMI = 3.830 + 0.0143 × ISBW described for use in feedlot steers by the

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      , where ISBW is initial shrunk BW. Baseline values represented the use of all available technologies in 2020 (monensin, a combination implant, and RH). From these values, the performance for the monensin, implant and monensin, implant, and no technology groups were calculated by removing the performance enhancements associated with each technology.
      In the groups that did not receive an implant in 2020, final BW was decreased by 7.46% and ADG was decreased by 20.0% as reported for implants containing a combination of androgenic and estrogenic hormones by
      • Duckett S.K.
      • Andrae J.G.
      Implant strategies in an integrated beef production system..
      . For the non-implanted cattle, G:F was decreased by 15.6% (
      • Duckett S.K.
      • Andrae J.G.
      Implant strategies in an integrated beef production system..
      ). For the cattle not fed monensin, there were no adjustments to initial or final BW (
      • Duffield T.F.
      • Merrill J.K.
      • Bagg R.N.
      Meta-analysis of the effects of monensin in beef cattle on feed efficiency, body weight gain, and dry matter intake..
      ). Average daily gain of cattle not fed monensin was decreased 2.5%, and DMI was increased by 3.2% as described by
      • Duffield T.F.
      • Merrill J.K.
      • Bagg R.N.
      Meta-analysis of the effects of monensin in beef cattle on feed efficiency, body weight gain, and dry matter intake..
      . Based on previous research conducted by
      • Beck P.
      • Hess T.
      • Hubbell D.
      • Hufstedler G.D.
      • Fieser B.
      • Caldwell J.
      Additive effects of growth promoting technologies on performance of grazing steers and economics of the wheat pasture enterprise..
      , additive effects were assumed when using implants and monensin in combination.
      Ractopamine hydrochloride was assumed to be fed during the final 28 d before slaughter according to practices commonly used by feedlot nutritionists (
      • 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..
      ) and within label recommendations. Excluding RH decreased final BW by 1.3% and ADG by 15.3% compared with diets with RH (
      • Gruber S.L.
      • Tatum J.D.
      • Engle T.E.
      • Mitchell M.A.
      • Laudert S.B.
      • Schroeder A.L.
      • Platter W.J.
      Effects of ractopamine supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type..
      ). The model did not adjust DMI for cattle fed RH, which agrees with the majority of published literature (

      Schroeder, A. L., D. M. Polser, S. B. Laudert, G. J. Vogel, T. Ripberger, and M. T. Van Koevering. 2004. The effect of Optaflexx on growth performance and carcass traits of steers and heifers. Pages 65–72 in Proc. Southwest Nutr. Manage. Conf., Univ. Arizona, Tucson.

      ;
      • Abney C.S.
      • Vasconcelos J.T.
      • McMeniman J.P.
      • Keyser S.A.
      • Wilson K.R.
      • Vogel G.J.
      • Galyean M.L.
      Effects of ractopamine hydrochloride on performance, rate and variation in feed intake, and acid-base balance in feedlot cattle..
      ;
      • Quinn M.J.
      • Reinhardt C.D.
      • Loe E.R.
      • Depenbusch B.E.
      • Corrigan M.E.
      • May M.L.
      • Drouillard J.S.
      The effects of ractopamine-hydrogen chloride (Optaflexx) on performance, carcass characteristics, and meat quality of finishing feedlot heifers..
      ;
      • López-Carlos M.A.
      • Ramírez R.G.
      • Aguilera-Soto J.I.
      • Aréchiga C.F.
      • Méndez-Llorente F.
      • Rodríguez H.
      • Silva J.M.
      Effect of ractopamine hydrochloride and zilpaterol hydrochloride on growth, diet digestibility, intake and carcass characteristics of feedlot lambs..
      ).
      The effects of RH, monensin, and implants on animal performance were also assumed to be additive in the 2020 model (
      • Bryant T.C.
      • Engle T.E.
      • Galyean M.L.
      • Wagner J.J.
      • Tatum J.D.
      • Anthony R.V.
      • Laudert S.B.
      Effects of ractopamine and trenbolone acetate implants with or without estradiol on growth performance, carcass characteristics, adipogenic enzyme activity, and blood metabolites in feedlot steers and heifers..
      ). Dressing percentage for the all technology group was increased to 64.0% in the 2020 model (personal communication, Ty Lawrence). Based on data published by
      • Quinn M.J.
      • Walter L.J.
      • Swingle R.S.
      • Defoor P.J.
      • Harper L.B.
      • Lawrence T.E.
      Comparison of the effects of Actogain or Optaflexx on finishing feedlot steer performance and carcass characteristics..
      , the DP of cattle not fed RH was decreased by 0.34% points. In addition, if cattle were not provided a combination implant, DP was decreased by 0.32% points (
      • Reinhardt C.D.
      • Wagner J.J.
      High-dose anabolic implants are not all the same for growth and carcass traits of feedlot steers: A meta-analysis..
      ).
      A C-footprint analysis was also conducted and included CO2e sources: enteric CH4, manure CH4, and nitrous oxide (N2O); indirect N2O production from feedyard ammonia emissions, processing of grain, and transport of feed and manure (
      • Cole N.A.
      • Parker D.B.
      • Brown M.S.
      • Jennings J.S.
      • Hales K.E.
      • Gunter S.A.
      Effects of steam flaking on the carbon-footprint of finishing beef cattle..
      ). The C-footprint of feed equipment and facilities was not included in our analyses. Animal respiratory CO2 emissions and net emissions of soil-C from manure application were assumed to be zero. Animal respiration CO2e is not a net source of greenhouse gas (

      Steinfeld, H., P. Gerber, T. Wassenaaar, V. Castel, M. Rosales, and C. DeHaan. 2006. Livestock’s Long Shadow: Environmental Issues and Options. Food Agric. Org. United Nations. Accessed Jul. 14, 2021. ftp://ftp.fao.org/docrep/fao/010/a0701e/a0701e00.pdf.

      ;
      • Cole N.A.
      • Parker D.B.
      • Brown M.S.
      • Jennings J.S.
      • Hales K.E.
      • Gunter S.A.
      Effects of steam flaking on the carbon-footprint of finishing beef cattle..
      ), and there is only a marginal decrease in soil-C on land used to produce crops the animals consumed and where manure was applied and respiratory losses are derived (
      • Schlesinger W.H.
      • Amundson R.
      Managing for soil carbon sequestration: Let’s get realistic..
      ;
      • Cole N.A.
      • Parker D.B.
      • Brown M.S.
      • Jennings J.S.
      • Hales K.E.
      • Gunter S.A.
      Effects of steam flaking on the carbon-footprint of finishing beef cattle..
      ).
      All greenhouse gas emissions were converted to constant CO2e. We used the GWP of 1 for CO2, 25 for CH4, and 298 for N2O (

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ,

      IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

      ). In our calculation of the C-footprint, we estimated the GWP of natural gas used in the steam flaking process to be 25 × CO2. A 5-region C-footprint analysis of crops fed to dairy cattle was conducted by
      • Adom F.
      • Maes A.
      • Workman C.
      • Clayton-Nierderman Z.
      • Thoma G.
      • Shonnard D.
      Regional carbon footprint analysis of dairy feeds for milk production in the USA..
      . The analysis included the C-footprint of herbicides, fertilizers, and so on that were used in crop production, but the C-footprint of equipment used in the farming process was not included. The C-footprint reported by
      • Adom F.
      • Maes A.
      • Workman C.
      • Clayton-Nierderman Z.
      • Thoma G.
      • Shonnard D.
      Regional carbon footprint analysis of dairy feeds for milk production in the USA..
      varied by region; thus, the average of the Great Plains and Midwest regions were used in the current C-footprint analysis because most cattle on feed in the United States are fed within these regions. Therefore, the following geometric mean C-footprints were used: (1) corn grain, 390 kg of CO2e/1,000 kg of DM; (2) alfalfa hay, 200 kg of CO2e/1,000 kg of DM; (3) soybean meal, 460 kg of CO2e/1,000 kg of DM; (4) miscellaneous feed additives used the same value as soybean meal (460 kg of CO2e/1,000 kg of DM); and (5) WDGS, 330 kg of CO2e/1,000 kg of DM. It is likely that there are differences in the C-footprint of ingredients produced in 1990 versus 2020; however, these differences are not known with certainty, and the C-footprints used in the analyses were those reported by
      • Adom F.
      • Maes A.
      • Workman C.
      • Clayton-Nierderman Z.
      • Thoma G.
      • Shonnard D.
      Regional carbon footprint analysis of dairy feeds for milk production in the USA..
      .
      The C-footprint of distillers grains production is variable, depending on production methodology and assumptions used in the calculations (
      • Kim S.
      • Dale B.E.
      Allocation procedure in ethanol production system from corn grain i. System expansion..
      ;
      • Searchinger T.
      • Heimlich R.
      • Houghton R.A.
      • Dong F.
      • Elobeid A.
      • Fabiosa J.
      • Tokgoz S.
      • Hayes D.
      • Yu T.-H.
      Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change..
      ;
      • Hünerberg M.
      • Little S.M.
      • Beauchemin K.A.
      • McGinn S.M.
      • O’Connor D.
      • Okine E.K.
      • Harstad O.M.
      • Kröbel R.
      • McAllister T.A.
      Feeding high concentrations of corn dried distillers’ grains decreases methane, but increases nitrous oxide emissions from beef cattle production..
      ). The proportions of the total C-footprint for grain ethanol production can be assigned to ethanol and the byproduct distillers grains based on mass, energy content, or economic value. Therefore, it is unclear what proportion of the C-footprint of ethanol should be allotted to the ethanol industry and what proportion should be allotted or credited when using an ethanol byproduct in cattle feeding, such as WDGS. To equally distribute the C-footprint of WDGS across both industries by mass, we assigned 50% of the C-footprint to the ethanol industry and 50% to the beef industry (total C-footprint of WDGS is 660 kg of CO2e/1,000 kg of DM). Therefore, in the present C-footprint analysis, we assumed the C-footprint of WDGS was 330 kg of CO2e/1,000 kg of DM.
      Enteric CH4 emissions were calculated using the feedlot enteric CH4 model used in the USDA-OCE 2014 publication (

      Powers, W., B. Auvermann, N. A. Cole, C. Gooch, R. Grant, J. Hatfield, P. Hunt, K. Johnson, A. Leytem, W. Liao, and J. M. Powell. 2014. Chapter 5: Quantifying greenhouse gas sources and sinks in animal production systems. Pages 5.5–5.160 in Quantifying Greenhouse Gas Fluxes in Agriculture and Forestry: Methods for Entity-Scale Inventory. Tech. Bull. No. 1939. M. Eve, D. Pape, M. Flugge, R. Steele, D. Man, M. Riley-Gilbert, and S. Biggar, ed. Office Chief Econ., USDA.

      ). The model assumes that the Ym (CH4 production as a percentage of gross energy intake) is 3.0% (

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ); however, adjustments are made based on ionophore inclusion, supplemental fat inclusion, grain type, and grain concentration. In the instance where monensin was included in the diet, the Ym was adjusted down in the equation for enteric CH4. Methane production in grams per day is then calculated from the adjusted Ym.
      Manure CH4 production was determined from volatile solid (VS; i.e., OM) excretion using the methods of

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ,

      IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

      ), where CH4 production = VS excretion × the maximum potential CH4 emission (Bo) × the CH4 conversion factor (MCF). The MCF is the percentage of Bo emitted and is based on manure handling factors and environmental conditions. For our calculations, VS excretion was estimated from DMI and OM digestibility (assumed to be 72% for these diets), and we assumed the diets contained 95% OM. Assuming the environmental conditions were a drylot in a temperate environment, a Bo of 0.19 m3/kg of VS and an MCF of 1.5% were used (

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ,

      IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

      ).
      Nitrogen excretion was calculated as the difference in N intake and N retention from ADG and BW (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ). Direct N2O emissions from manure were estimated to be 2.0% of N excreted (

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ,

      IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

      ), whereas the indirect N2O emissions were estimated assuming that 65.0% of the N excreted was lost as ammonia (
      • Todd R.W.
      • Cole N.A.
      • Clark R.N.
      • Flesch T.K.
      • Harper L.A.
      • Baek B.H.
      Ammonia emissions from a beef cattle feedyard on the southern High Plains..
      ) and, subsequently, that 1.0% of the ammonia-N was lost as N2O (

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      ,

      IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

      ). The amount of enteric N2O emissions only accounts for less than 0.5% of total CO2e (
      • Parker D.B.
      • Meyer B.
      • Jennings T.
      • Jennings J.
      • Dougherty H.
      • Cole N.A.
      • Casey K.
      Enteric nitrous oxide emissions from beef cattle..
      ;
      • Cole N.A.
      • Meyer B.E.
      • Parker D.B.
      • Neel J.
      • Turner K.E.
      • Northup B.K.
      • Jennings T.
      • Jennings J.S.
      Effects of diet quality on energy metabolism and methane production by beef steers fed a warm-season grass-based hay diet..
      ). The quantity of manure collected and transported to be field applied was estimated based on
      • Buttrey E.K.
      • Cole N.A.
      • Jenkins K.H.
      • Meyer B.E.
      • McCollum III, F.T.
      • Preece S.L.M.
      • Auvermann B.W.
      • Heflin K.R.
      • MacDonald J.C.
      Effects of twenty percent corn wet distillers grains plus solubles in steam-flaked and dry-rolled corn-based finishing diets on heifer performance, carcass characteristics, and manure characteristics..
      , where the quantity of manure DM collected from treatment pens was reported. We estimated the DM content of the collected manure to be 65.0%, which was used to calculate the total quantity of manure collected and land applied. For simplicity, we assumed that all manure was transported a common distance of 20 km.
      The C-footprint of transporting feed grains to the feedlot and to collect and transport manure to fields for application were calculated assuming a constant energy cost of 149.6 kg of CO2e/t-km (
      • Hünerberg M.
      • Little S.M.
      • Beauchemin K.A.
      • McGinn S.M.
      • O’Connor D.
      • Okine E.K.
      • Harstad O.M.
      • Kröbel R.
      • McAllister T.A.
      Feeding high concentrations of corn dried distillers’ grains decreases methane, but increases nitrous oxide emissions from beef cattle production..
      ). We estimated that all feedstuffs excluding WDGS were transported an average of 200 km to the feedlot. Wet distillers grains plus solubles are typically not trucked long distances to be fed; thus, we assumed they were hauled 50 km. The subsequent manure was hauled an average of 20 km, and the average distance to haul feed from the mill to the feed bunk was 3.2 km/1,000 kg of feed DM. Our estimates were based on a 50,000-animal-capacity feedlot with 130 ha of cattle pen area. The feed delivery logistics that we used were described by
      • da Silva J.C.B.
      • Cole N.A.
      • Ponce C.H.
      • Smith D.R.
      • Greene L.W.
      • Schuster G.
      • Brown M.S.
      Effects of supplemental fat concentration on feeding logistics, animal performance, and nutrient losses of heifers fed finishing diets based on steam-flaked corn and sorghum-based distiller’s grains..
      and
      • Ponce C.H.
      • Cole N.A.
      • Sawyer J.
      • da Silva J.C.B.
      • Smith D.R.
      • Maxwell C.
      • Brown M.S.
      Effects of wet corn distiller’s grains with solubles and nonprotein nitrogen on feeding efficiency, growth performance, carcass characteristics, and nutrient losses of yearling steers..
      , who estimated bulk densities of the diet and DM concentration and assumed a DMI.

      RESULTS AND DISCUSSION

      Because the performance and C-footprint values reviewed in this study were based on deterministic model estimates, no statistical analysis was conducted. Therefore, all data comparisons discussed will include consideration of numerical differences only.

      Dietary Changes from 1990 to 2020

      The ingredient and nutrient composition of feedlot diets in 1990 versus 2020 is presented in Table 1. One of the major dietary changes of note from 1990 compared with 2020 is the inclusion of fibrous grain-milling byproducts as a replacement for more expensive sources of energy and CP such as steam-flaked corn and soybean meal. High concentrations of digestible fiber and protein present within these feedstuffs allow a portion of the high-starch grains traditionally used in feedlot diets to be replaced, thus in some instances improving growth performance of cattle (
      • Hussein H.S.
      • Berger L.L.
      Effects of feed intake and dietary level of wet corn gluten feed on feedlot performance, digestibility of nutrients, and carcass characteristics of growing-finishing beef heifers..
      ;
      • Buttrey E.K.
      • Jenkins K.H.
      • Lewis J.B.
      • Smith S.B.
      • Miller R.K.
      • Lawrence T.E.
      • McCollum III, F.T.
      • Pinedo P.J.
      • Cole N.A.
      • MacDonald J.C.
      Effects of 35% corn wet distillers grains plus solubles in steam-flaked and dry-rolled corn-based finishing diets on animal performance, carcass characteristics, beef fatty acid composition, and sensory attributes.
      ;
      • Ponce C.H.
      • Cole N.A.
      • Sawyer J.
      • da Silva J.C.B.
      • Smith D.R.
      • Maxwell C.
      • Brown M.S.
      Effects of wet corn distiller’s grains with solubles and nonprotein nitrogen on feeding efficiency, growth performance, carcass characteristics, and nutrient losses of yearling steers..
      ) while potentially mitigating ruminal acidosis (
      • Krehbiel C.
      • Stock R.
      • Herold D.
      • Shain D.
      • Ham G.
      • Carulla J.
      Feeding wet corn gluten feed to reduce subacute acidosis in cattle..
      ). Although distillers grains were fed in limited amounts 100 yr ago, the increased demand for grain alcohol as a fuel source has made this feedstuff more widely available (
      • Klopfenstein T.J.
      • Erickson G.E.
      • Bremer V.R.
      Board-Invited Review: Use of distillers by-products in the beef cattle feeding industry..
      ). More recently, increased use of artificial sweeteners and oils has also increased the availability of wet corn gluten feed from the wet milling of corn.
      Because use of ethanol byproducts such as WDGS has increased, the cost per unit of dietary CP has decreased, thereby resulting in the 2020 feedlot diets having greater CP compared with 1990 (15.42 vs. 12.50% CP on a DM basis for 2020 and 1990, respectively). In a survey conducted by
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      , dietary CP ranged from 12.5 to 14.4% of DM, and by 2016,
      • 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 recommended CP concentrations ranged from 13.0 to 14.3% of DM in finishing diets. The slightly greater CP used in the 2020 model than that reported by
      • 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..
      is likely because urea was added to the diet in an effort to meet cattle requirements for RDP when feeding diets using WDGS as the sole byproduct. However,
      • 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..
      also identified a maximum tolerable concentration of 20.0% CP in finishing cattle diets and suggested that it is possible that some nutritionists were using greater than the recommended CP concentrations described previously because of the increased inclusion of high CP byproducts such as WDGS. Therefore, the authors felt the CP concentration of 15.42% was within the acceptable range for the 2020 diet.
      In addition to changes in dietary CP, differences in both fat and starch concentrations from 1990 to 2020 are likely a function of incorporating WDGS into the diet. For example, dietary fat concentrations increased from 1990 to 2020 (5.17 vs. 6.87%), despite similar concentrations of added fat from tallow, yellow grease, or other fat sources. According to the

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      , steam-flaked corn, soybean meal, and WDGS contain 3.19, 1.88, and 10.84% fat, respectively, suggesting that the greater fat concentration in the 2020 diet is a function of the greater contribution of fat from WDGS, as this byproduct replaced both steam-flaked corn and soybean meal in the diet. In contrast, dietary starch concentrations decreased (66.67 and 51.35% starch in 1990 and 2020, respectively) as WDGS replaced steam-flaked corn in the diet. The process of ethanol production uses starch as the main substrate for fermentation, thereby decreasing starch and concentrating the remaining fiber, protein, and fat within residual byproducts such as WDGS (
      • Bothast R.
      • Schlicher M.
      Biotechnological processes for conversion of corn into ethanol..
      ). Another consequence of the addition of byproducts to the current diets is greater concentrations of dietary phosphorus, which required greater inclusion of a supplementary source of calcium to maintain a 2:1 ratio of Ca:P. Overall, the concentration of CP, fat, and fiber has increased and starch has decreased between 1990 and 2020, resulting in greater net energy concentrations in 2020 compared with 1990.

      Technology Effects on Cattle Growth and Emissions

      Administration of anabolic implants is a common management practice used to increase ADG of feedlot cattle and has been widespread since the development of diethylstilbestrol in 1957 (
      • Raun A.
      • Preston R.
      History of diethylstilbestrol use in cattle..
      ). Just before 1990, trenbolone acetate was approved for use in growth-promoting implants for feedlot cattle (

      FOIA (Freedom of Information Act). 1987. Finaplix. US Food Drug Admin.

      ). Trenbolone acetate is a synthetic anabolic steroid that has 3 to 5 times the androgenic activity and 8 to 10 times the anabolic activity of testosterone (

      Bouffault, J., and J. Willemart. 1983. Anabolic activity of trenbolone acetate alone or in association with estrogens. Pages 155–179 in Anabolics in Animal Production. E. Meissonnier, ed. Office Int. Epizooties.

      ). A common management practice today includes the use of combination implants containing both estrogen and trenbolone acetate. The most recent survey describing implant use in beef cattle indicates that 92.3% of all feedlot cattle receive at least one implant during their lifetime (

      USDA-NAHMS. 2013. Trends in Health and Management Practices on US Feedlots, 1994–2011. USDA Natl. Anim. Health Monit. Syst.

      ). Growth-promoting implants increased ADG, final BW, hot carcass weight (HCW), DMI, and G:F in 1990 (Table 2) and 2020 (Table 3). In 1990 DP was decreased when an implant was used. However, the use of combination implants in 2020 increased DP. Use of estrogenic compounds, androgenic compounds, or both, increases DMI, which could increase gut fill and subsequently reduce DP (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      ). However, when used alone or in combination with estrogen, greater protein deposition within the carcass from administration of trenbolone acetate could offset the contribution of gut fill and increase DP (
      • Duckett S.K.
      • Andrae J.G.
      Implant strategies in an integrated beef production system..
      ). Furthermore, because the use of implants increased ADG at a similar proportion to the increase in final BW, the total number of DOF was comparable (0 additional DOF in 1990 and 1 in 2020) between cattle receiving either no technology or implants in both 1990 and 2000. The greater DMI in 1990 and 2020 with the use of implants caused manure production, N excretion, and enteric CH4 production to increase. However, when calculated per kilogram of total BW gain (data not shown), manure production, N excretion, and enteric CH4 production all decreased.
      Table 2Growth performance model for feedlot cattle finished using technologies available in 1990
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      Initial BW, kg335335335335
      Final BW, kg500535500535
      Days on feed, d137137134135
      ADG, kg1.211.461.231.48
      DMI, kg8.559.088.218.73
      G:F0.1420.1610.1500.170
      DP, %63.1663.0063.1663.00
      HCW,
      HCW = hot carcass weight.
      kg
      316337316337
      Enteric CH4
       g/d80.9685.9874.7579.49
       L/kg of DMI13.2213.2212.7212.72
      Total N balance during entire feeding period
       N intake, kg23.4324.8822.0023.57
       N excreted, kg20.5621.5319.1320.25
       Ammonia-N, kg15.2316.1714.3015.32
      Total manure excretion during entire feeding period
       Manure, kg of DM/animal273290256275
       Manure, kg as is/animal420446394422
      1 Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      2 Cattle received monensin.
      3 HCW = hot carcass weight.
      Table 3Growth performance model for feedlot cattle finished using technologies available in 2020
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      RH
      Cattle received ractopamine hydrochloride the last 28 d of feeding.
      Imp, Mon, and RH
      Initial BW, kg360360360360360360
      Final BW, kg602647602647610655
      Days on feed, d182183181179185179
      ADG, kg1.331.561.341.601.351.65
      DMI, kg8.899.288.658.988.948.98
      G:F0.1500.1720.1540.1790.1540.184
      DP, %63.3463.6663.3463.6663.6864.00
      HCW,
      HCW = hot carcass weight.
      kg
      381412381412388419
      Enteric CH4
       g/d87.3691.2081.7484.8587.8584.85
       L/kg of DMI13.7213.7213.2013.2013.7213.20
      Total N balance during entire feeding period
       N intake, kg39.9241.9038.6339.6640.8139.66
       N excreted, kg36.1437.9735.0035.6537.1135.59
       Ammonia-N, kg25.9527.2325.1125.7826.5225.78
      Total manure excretion during entire feeding period
       Manure, kg of DM/animal377396365375385375
       Manure, kg as is/animal580609561576593576
      1 Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      2 Cattle received monensin.
      3 Cattle received ractopamine hydrochloride the last 28 d of feeding.
      4 HCW = hot carcass weight.
      Ionophores are a feed additive used to improve feed efficiency (
      • Goodrich R.D.
      • Garrett J.E.
      • Gast D.R.
      • Kirick M.A.
      • Larson D.A.
      • Meiske J.C.
      Influence of monensin on the performance of cattle..
      ) and animal health by decreasing the risk for subclinical acidosis (
      • Stock R.A.
      • Laudert S.B.
      • Stroup W.W.
      • Larson E.M.
      • Parrott J.C.
      • Britton R.A.
      Effect of monensin and monensin and tylosin combination on feed intake variation of feedlot steers..
      ;
      • McGuffey R.K.
      • Richardson L.F.
      • Wilkinson J.I.D.
      Ionophores for dairy cattle: Current status and future outlook..
      ;
      • Birkelo C.P.
      Pharmaceuticals, direct-fed microbials, and enzymes for enhancing growth and feed efficiency of beef cattle..
      ;
      • Erickson G.E.
      • Milton C.T.
      • Fanning K.C.
      • Cooper R.J.
      • Swingle R.S.
      • Parrott J.C.
      • Vogel G.
      • Klopfenstein T.J.
      Interaction between bunk management and monensin concentration on finishing performance, feeding behavior, and ruminal metabolism during an acidosis challenge with feedlot cattle..
      ). Ionophore use has been widespread throughout the feedlot industry for many years (
      • Galyean M.L.
      Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
      ;
      • 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..
      ). Monensin sodium is the most commonly used ionophore (
      • 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..
      ) and was originally approved for use in beef cattle in 1975 (
      • Goodrich R.D.
      • Garrett J.E.
      • Gast D.R.
      • Kirick M.A.
      • Larson D.A.
      • Meiske J.C.
      Influence of monensin on the performance of cattle..
      ). In addition to growth performance and health benefits, monensin has the potential to reduce CH4 emissions (
      • Tedeschi L.O.
      • Fox D.G.
      • Tylutki T.P.
      Potential environmental benefits of ionophores in ruminant diets..
      ;
      • McGinn S.M.
      • Beauchemin K.A.
      • Coates T.
      • Colombatto D.
      Methane emissions from beef cattle: Effects of monensin, sunflower oil, enzymes, yeast, and fumaric acid..
      ;
      • Tedeschi L.O.
      Potential environmental benefits of feed additives and other strategies for ruminant production..
      ;
      • Hemphill C.N.
      • Wickersham T.A.
      • Sawyer J.E.
      • Brown-Brandl T.M.
      • Freetly H.C.
      • Hales K.E.
      Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance..
      ). Increased growth performance and decreased CH4 production observed in cattle consuming monensin are accomplished primarily via the reduction of gram-positive bacteria in the rumen (
      • Goodrich R.D.
      • Garrett J.E.
      • Gast D.R.
      • Kirick M.A.
      • Larson D.A.
      • Meiske J.C.
      Influence of monensin on the performance of cattle..
      ;
      • Cheng K.J.
      • McAllister T.A.
      • Popp J.D.
      • Hristov A.N.
      • Mir Z.
      • Shin H.T.
      A review of bloat in feedlot cattle..
      ;
      • Birkelo C.P.
      Pharmaceuticals, direct-fed microbials, and enzymes for enhancing growth and feed efficiency of beef cattle..
      ). Monensin does not directly inhibit methanogen growth but inhibits H2-producing bacteria and limits the total H2 available for methane production (
      • Chen M.
      • Wolin M.J.
      Effect of monensin and lasalocid-sodium on the growth of methanogenic and rumen saccharolytic bacteria..
      ). Furthermore, monensin reduces CH4 production by inhibiting the decomposition of formate that is produced during the breakdown of pyruvate (
      • Van Nevel C.J.
      • Demeyer D.I.
      Effect of monensin on rumen metabolism in vitro..
      ).
      When cattle were fed monensin as the only performance-enhancing technology, final BW and HCW were not different compared with no technology for either of the time periods evaluated. In 1990 and in 2020, feeding monensin increased ADG by 0.01 kg. Inclusion of monensin in the model also decreased DMI by 0.34 and 0.24 kg in 1990 and 2020, respectively. The minor change in ADG combined with decreased DMI resulted in a 5.6% increase in G:F in 1990 and 2.7% in 2020 when monensin was used compared with no technology. The improvement in G:F decreased the DOF by 3 d in 1990 and 1 d in 2020. The reduction in DMI resulted in decreased manure production, N intake, and enteric CH4. Likewise, monensin has been reported to decrease the dietary gross energy lost as CH4 in beef cattle (
      • Ranga Niroshan Appuhamy J.A.D.
      • Strathe A.B.
      • Jayasundara S.
      • Wagner-Riddle C.
      • Dijkstra J.
      • France J.
      • Kebreab E.
      Anti-methanogenic effects of monensin in dairy and beef cattle: A meta-analysis..
      ;
      • Hemphill C.N.
      • Wickersham T.A.
      • Sawyer J.E.
      • Brown-Brandl T.M.
      • Freetly H.C.
      • Hales K.E.
      Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance..
      ).
      When used together, the effects of both a growth-promoting implant and monensin were additive. Therefore, final BW of cattle in the implant and monensin group increased by 35.0 kg in 1990 (Table 2) and 45.0 kg in 2020 (Table 3) compared with no technology. Using both implants and monensin increased ADG by 0.27 kg in 1990 and 2020. Implants typically increase DMI and monensin decreases DMI; thus, using both technologies together resulted in a slightly increased DMI in 1990 (8.55 vs. 8.73 kg) and in 2020 (8.89 vs. 8.98 kg) when compared with not using technologies. As implants and monensin both increase G:F when used independently, the G:F is further increased in relation to no technology when the 2 technologies are used in combination. Because of these improvements in efficiency, enteric CH4, excreted N, and manure output were all decreased when implants and monensin were used in combination.
      Most recently, provision of a βAA for the last 28 to 42 d of the finishing period has become prevalent in the feedlot industry (
      • 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..
      ). β-Adrenergic agonists increase lean tissue growth by binding to β-adrenergic receptors present in the plasma membrane of both muscle and adipose tissue, which initiates a signaling cascade that results in lean tissue hypertrophy (
      • Lynch G.S.
      • Ryall J.G.
      Role of β-adrenoceptor signaling in skeletal muscle: Implications for muscle wasting and disease..
      ). The mechanism of lean muscle growth is not fully understood but could be because of increased protein synthesis, decreased protein degradation, or both (
      • Smith S.B.
      • Garcia D.K.
      • Anderson D.B.
      Elevation of a specific mRNA in longissimus muscle of steers fed ractopamine..
      ). Ractopamine hydrochloride was first approved in 2003, and in 2020 was the only βAA used in the United States.
      In the period between 1990 and 2020, use of RH became a common cattle management strategy and therefore was added as an additional technology in the 2020 model that could not be reported in the 1990 model. Ractopamine hydrochloride compared with no technology increased final BW by 1.3%, increased ADG by 1.5%, and increased G:F by 2.7%. In addition, DP was increased when RH was fed compared to no technology (63.3 vs. 63.7%). When all 3 technologies were used in 2020, DMI increased slightly compared with no technology and ADG was improved by 24.1%, resulting in a 22.7% increase in G:F, which decreased DOF by 3 d. The DP of cattle administered all technologies increased by 1.0% compared with no technology. The improvements in growth performance and feed efficiency associated with the use of all technologies decreased enteric CH4 (g/d) by 3.0% and liters per kilogram of DMI by 3.9% compared with no technology. In addition, use of all technologies in 2020 decreased N excretion per animal by 1.6%.

      MacDonald, J., N. A. Cole, J. Osterstock, and K. E. Hales. 2009. Technology in the Industry—Where Would We, and the World, Be Without It? Planis Nutr. Counc.

      indicated that use of implants, monensin, and a β-agonist decreased estimated enteric methane per animal by 7.6% and manure nitrogen of cattle by 5.7% when fed a 12.0% forage and 12.5% CP diet for 150 d. The greater difference observed by

      MacDonald, J., N. A. Cole, J. Osterstock, and K. E. Hales. 2009. Technology in the Industry—Where Would We, and the World, Be Without It? Planis Nutr. Counc.

      may be caused by greater DMI (9.36 kg). These data indicate sustainability of feedlot cattle production has improved through the use of technologies by decreasing the outputs that contribute to GWP.

      Effects of the Overall Production System on Cattle Growth and Emissions (1990 vs. 2020)

      Because of the differences in management practices and available technologies incorporated into the cattle management system from 1990 to 2020, direct comparisons of production outcomes between 1990 and 2020 should be interpreted with caution. However, the use of all technologies (implant and monensin in 1990 and implant, monensin, and RH in 2020) best represents the practices used on the majority of feedlots and should be representative of the cattle fed in each time period. Therefore, comparisons between 1990 and 2020 will only describe the combination of all available technologies within each year. From 1990 (Table 2) to 2020 (Table 3), the initial BW, final BW, and HCW increased by 7.5, 22.4, and 24.3% respectively. In addition to the increase in final BW, ADG increased from 1.48 to 1.65 kg/d, with an increase in DMI from 8.55 to 8.98 kg. This resulted in an 8.2% increase in G:F. Although a greater ADG was demonstrated in 2020 compared with 1990, the number of DOF was increased by 44 d to achieve the 95.0 kg of additional BW gain produced in 2020.
      Daily enteric CH4 production was less for cattle in feedlots in 1990 (79.49 g/d) compared with 2020 (84.85 g/d) because of less DMI in 1990. Reporting CH4 as a proportion of DMI removes differences in intake and represents how diets affect CH4 emissions. When CH4 is expressed as liters per kilogram of DMI to account for differences in DMI, the cattle fed in 2020 produced slightly more CH4 per kilogram of DMI than cattle in 1990 (13.20 vs. 12.72 L/kg of DMI) because the 2020 diet had greater calculated gross energy (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ) than the 1990 diet. Additionally, total fat and NDF concentrations in the diet increased from 1990 to 2020. It has been documented that increasing the dietary fat concentration can reduce CH4 production (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

      ;
      • Drehmel O.R.
      • Brown-Brandl T.M.
      • Judy J.V.
      • Fernando S.C.
      • Miller P.S.
      • Hales K.E.
      • Kononoff P.J.
      The influence of fat and hemicellulose on methane production and energy utilization in lactating Jersey cattle..
      ). However, increased NDF concentrations can increase CH4 production (
      • Hales K.E.
      • Brown-Brandl T.M.
      • Freetly H.C.
      Effects of decreased dietary roughage concentration on energy metabolism and nutrient balance in finishing beef cattle..
      ). The equations used in this model for enteric CH4 production (

      Powers, W., B. Auvermann, N. A. Cole, C. Gooch, R. Grant, J. Hatfield, P. Hunt, K. Johnson, A. Leytem, W. Liao, and J. M. Powell. 2014. Chapter 5: Quantifying greenhouse gas sources and sinks in animal production systems. Pages 5.5–5.160 in Quantifying Greenhouse Gas Fluxes in Agriculture and Forestry: Methods for Entity-Scale Inventory. Tech. Bull. No. 1939. M. Eve, D. Pape, M. Flugge, R. Steele, D. Man, M. Riley-Gilbert, and S. Biggar, ed. Office Chief Econ., USDA.

      ) did not account for differences in dietary analysis. Total N intake throughout the feeding period was greater in 2020 (39.66 kg per animal) compared with 1990 (23.57 kg per animal), thus resulting in greater total N excretion in 2020 compared with 1990 (35.59 vs. 20.25 kg per animal). The greater N intake in 2020 versus 1990 is because of the greater dietary CP as a result of inclusion of byproducts in the 2020 diet. The increased DOF and daily DMI, and the inclusion of WDGS, resulted in a 36.4% increase in total manure DM output per animal across the feeding period and 36.5% increase in as-is total manure per animal.

      Technology Effects on Total Carbon Footprint

      Because CH4 and other greenhouse gas emissions have different impacts on the environment, it is important to convert them to a CO2e basis. All emissions sources in 1990 (Table 4) and in 2020 (Table 5) increased when implants were used because of increased DMI. The increased DMI is supported by the equations established by
      • Fox D.G.
      • Sniffen C.J.
      • O’Connor J.D.
      • Russell J.B.
      • Van Soest P.J.
      A net carbohydrate and protein system for evaluating cattle diets: III. Cattle requirements and diet adequacy..
      indicating hormonal implants containing estrogenic compounds increase DMI. Therefore, in 1990 and 2020, implants increased total CO2e per animal by 6.0 and 5.0%, respectively. Although total emissions were increased with the use of implants, when expressed per unit of BW gain, implants decreased kilograms of CO2e per kilogram of BW gain by 0.73 kg in 1990 and 0.64 kg in 2020. Because DP was decreased in 1990 and increased in 2020 for implants, the decrease in kilograms of CO2e per kilogram of HCW was 0.6 and 2.8% in 1990 and 2020, respectively.
      • Stackhouse K.R.
      • Rotz C.A.
      • Oltjen J.W.
      • Mitloehner F.M.
      Growth-promoting technologies decrease the carbon footprint, ammonia emissions, and costs of California beef production systems..
      calculated that steers that received an implant in both the stocker and feedlot system had reduced CO2e per animal compared with cattle raised using a natural program that did not administer implants over their entire lifetime.
      Table 4Carbon footprint [kg of CO2 equivalents (CO2e) per animal] of feedlot cattle finished using different technologies available in 1990
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      Animal and manure
       Enteric CH4277.30294.49250.43268.27
       Manure N2O122.51128.35114.03120.68
       Manure CH418.5019.6517.3818.61
       Indirect N2O22.6924.1021.3122.83
      Crop production
       Corn349.02370.65327.80351.16
       Alfalfa hay30.4632.3428.6030.64
       Soybean meal26.9428.6125.3027.11
       Other30.1732.0428.3430.36
      Transport
       Feed42.1744.7939.6142.43
       Manure1.231.311.161.24
      Grain processing energy
       Natural gas26.8528.5125.2227.01
       Electricity14.7715.6813.8714.86
      Total production
       Total CO2e962.611,020.52893.04955.21
       kg of CO2e/kg of HCW
      HCW = hot carcass weight.
      3.053.032.832.83
       kg of CO2e/kg of BW gain5.835.105.414.78
      Total reactive N
       kg/animal15.5416.5014.5915.63
       g/kg of HCW49.2048.9446.2046.37
       g/kg of BW gain94.1782.4888.4378.14
      1 Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      2 Cattle received monensin.
      3 HCW = hot carcass weight.
      Table 5Carbon footprint [kg of CO2 equivalents (CO2e) per animal for the entire feeding period] of feedlot cattle finished using different technologies available in 2020
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      RH
      Cattle received ractopamine hydrochloride in the last 28 d of feeding.
      Imp, Mon,

      and RH
      Animal and manure
       Enteric CH4397.50417.22369.85379.72406.33379.72
       Manure N2O215.39226.33208.58212.50221.20212.09
       Manure CH425.5526.8224.7325.3926.1225.39
       Indirect N2O38.6640.5837.4138.4139.5238.41
      Crop production
       Corn412.68433.15399.33409.99421.84409.99
       Alfalfa hay29.1230.5728.1828.9329.7728.93
       Wet distillers grains plus solubles
      For carbon footprint of wet distillers grains plus solubles, 50% was applied to the ethanol industry and 50% to the wet distillers grains plus solubles.
      106.79112.08103.33106.09109.16106.09
       Other41.6843.7540.3341.4142.6041.41
      Transport
       Feed58.7061.6156.8058.3160.0058.31
       Manure1.701.791.651.691.741.69
      Grain processing energy
       Natural gas31.7433.3230.7231.5432.4531.54
       Electricity17.4618.3316.8917.3517.8517.35
      Total production
       Total CO2e1,376.991,445.551,317.811,351.331,408.581,350.92
       kg of CO2e/kg of HCW
      HCW = hot carcass weight.
      3.613.513.463.283.633.22
       kg of CO2e/kg of BW gain5.685.045.454.725.654.58
      Total reactive N
       kg/animal26.4927.8025.6326.3127.0826.31
       g/kg of HCW69.4467.5567.2663.9369.7762.77
       g/kg of BW gain109.3297.01106.0591.81108.5489.19
      1 Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      2 Cattle received monensin.
      3 Cattle received ractopamine hydrochloride in the last 28 d of feeding.
      4 For carbon footprint of wet distillers grains plus solubles, 50% was applied to the ethanol industry and 50% to the wet distillers grains plus solubles.
      5 HCW = hot carcass weight.
      As described previously, monensin decreased DMI and slightly increased ADG in both 1990 and 2020 compared with no technology. The increased ADG with no change in final BW resulted in 3 and 1 less DOF in 1990 and 2020, respectively. The decreased DMI and fewer DOF associated with monensin decreased the amount of CO2e from all sources, resulting in a reduction of total kilograms of CO2e per animal by 7.8% in 1990 and by 4.5% in 2020. The proportional decrease is the same when expressed as kilograms of CO2e per kilogram of BW gain when monensin is used because monensin did not increase the amount of BW gain during the feeding period.
      When implants and monensin were fed in combination in 1990, all emissions were either decreased or similar when compared with the no technology group when expressed per animal and per kilogram of BW gain. In 2020 all emissions decreased per animal and resulted in total emissions decreasing when expressed as kilograms of CO2e per animal compared with no technology. When implants and monensin were used in combination, the kilograms of CO2e per kilogram of BW gain was decreased from the no technology group by 22.0% in 1990 and by 20.3% in 2020. This indicates that in addition to the overall decrease in emissions when monensin and implants are used together, more BW gain is also obtained. Therefore, as cattle growth becomes more efficient, environmental impact decreases. The addition of RH in the 2020 model had little effect on kilograms of CO2e per animal because RH had no effect on DMI or DOF. However, because RH increases ADG with no effect on DMI or DOF, an additional decrease in kilograms of CO2e per kilogram of BW gain is captured. Thus, when all technologies were used in 2020, the kilograms of CO2e per kilogram of BW gain was decreased by 24.0% compared with no technology. Because the only available technologies in 1990 were monensin and implants, the 22.0% decrease in CO2e per kilogram of BW gain stated previously represents the effects of all technologies used in 1990. According to the

      IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      , growth technologies such as hormonal implants and ionophores have a technical reduction potential in North America of 9.0%, which is one of the largest reduction potentials in the world. The use of all available technologies in 1990 and 2020 reduced kilograms of CO2e per kilogram of HCW by 7.8 and 12.1%, respectively. In addition, the use of growth-promoting technologies in 2020 has had a larger effects on the CO2e per kilogram of BW gain in 2020 than in 1990 when compared with the use of no technologies in each year.

      Effects of the Overall Production System on Total Carbon Footprint (1990 vs. 2020)

      Overall, sources of emissions that have GWP from cattle and manure increased from 1990 (Table 4) to 2020 (Table 5) when expressed on a CO2e per animal basis and was caused by the 44 additional DOF and greater DMI in 2020. Corn grain in 1990 produced 351.16 kg of CO2e per animal and by 2020 increased by 16.8% to 409.99 kg of CO2e per animal. The decrease in inclusion rate of corn from 76.4 to 65.4% likely helped to offset the increased DMI and longer DOF that caused an increase in the C-footprint associated with growing corn. Soybean meal was removed from the diet from 1990 to 2020, thus eliminating its contribution. However, WDGS were added as a byproduct feed in the time between 1990 and 2020 and contribute 106.09 kg of CO2e per animal. Therefore, total crop production contribution of CO2e per animal increased from 439.27 kg in 1990 to 586.42 kg in 2020. If expressed on a basis of CO2e/100 kg of feed DM, in 1990 feed production contributed 37.27 CO2e/100 kg of feed DM and in 2020 contributed 36.48 CO2e/100 kg of feed DM (data not shown), indicating the effect of feed production has decreased. In addition, the proportion of total CO2e associated with feed has decreased from 46.0% (Table 6) to 43.4% (Table 7) but still has the greatest effect on the overall C-footprint.
      Table 6Carbon footprint (% of total carbon footprint) of feedlot cattle depending on technology use in 1990
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      Animal and manure
       Enteric CH428.8128.8628.0428.09
       Manure N2O12.7312.5812.7712.63
       Manure CH41.921.931.951.95
       Indirect N2O2.362.362.392.39
      Feed production
       Corn36.2636.3236.7136.76
       Alfalfa hay3.163.173.203.21
       Soybean meal2.802.802.832.84
       Other3.133.143.173.18
      Transport
       Feed4.384.394.444.44
       Manure0.1280.1280.1300.130
      Grain processing energy
       Natural gas2.792.792.822.83
       Electricity1.531.541.551.56
      Summary
       Enteric28.8128.8628.0428.09
       Manure17.0116.8617.1016.97
       Feed production45.3545.4345.9245.99
       Transport4.514.524.564.57
       Grain processing4.324.334.384.38
      1 Cattle received a growth-promoting implant that contained estradiol twice during the finishing period.
      2 Cattle received monensin.
      Table 7Carbon footprint (% of total carbon footprint) of feedlot cattle depending on technology use in 2020
      ItemNo technologyImp
      Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      Mon
      Cattle received monensin.
      Imp and

      Mon
      RH
      Cattle received ractopamine hydrochloride the last 28 d of feeding.
      Imp, Mon,

      and RH
      Animal and manure
       Enteric CH428.8728.8628.0728.1028.8528.11
       Manure N2O15.6415.6615.8315.7315.7015.70
       Manure CH41.861.861.881.881.851.88
       Indirect N2O2.812.812.842.842.812.84
      Feed production
       Corn29.9729.9630.3030.3429.9530.35
       Alfalfa hay2.122.112.142.142.112.14
       Wet distillers grains plus solubles
      For carbon footprint of wet distillers grains with solubles, 50% was applied to the ethanol industry and 50% to the wet distillers grains plus solubles.
      7.767.757.847.857.757.85
       Other3.033.033.063.063.023.07
      Transport
       Feed4.264.264.314.324.264.32
       Manure0.1240.1240.1250.1250.1240.125
      Grain processing energy
       Natural gas2.312.302.332.332.302.33
       Electricity1.271.271.281.281.271.28
      Summary
       Enteric28.8728.8628.0728.1028.8528.11
       Manure20.3120.3220.5420.4520.3620.42
       Feed production42.8742.8643.3443.4042.8443.41
       Transport4.394.394.444.444.384.44
       Grain processing3.573.573.613.623.573.62
      1 Cattle received a growth-promoting implant that contained trenbolone acetate and estradiol twice during the finishing period.
      2 Cattle received monensin.
      3 Cattle received ractopamine hydrochloride the last 28 d of feeding.
      4 For carbon footprint of wet distillers grains with solubles, 50% was applied to the ethanol industry and 50% to the wet distillers grains plus solubles.
      The CO2e per animal of feed transport to the feedlot has increased from 42.43 to 58.31 kg from 1990 to 2020 because animals are fed for an additional 44 DOF. Similarly, manure transport away from the feedlot increased from 1.24 to 1.69 kg of CO2e per animal because of the greater amount of manure produced, which is a result of the increased DOF in the 2020 model. The effects of natural gas and electricity required to steam flake corn has also increased from 1990 (27.01 and 14.86 kg of CO2e per animal, respectively) to 2020 (31.54 and 17.35 kg of CO2e per animal, respectively) because of the increase in dietary DMI per animal that was achieved from an increase in DOF. Although corn inclusion decreased from 1990 to 2020, total corn consumption per animal increased by 150.80 kg when comparing the all technology groups.
      Overall, cattle in 1990 produced 955.21 kg of CO2e per animal compared with 1,350.92 kg of CO2e per animal in 2020. These values are similar to those reported for California beef production by
      • Stackhouse-Lawson K.R.
      • Rotz C.A.
      • Oltjen J.W.
      • Mitloehner F.M.
      Carbon footprint and ammonia emissions of California beef production systems..
      . However, it is important to note these values are not scaled to the quantity of HCW produced. When using all available technologies, in 1990 cattle produced 2.83 kg of CO2e/kg of HCW compared with 3.22 kg of CO2e/kg of HCW in 2020. Because initial BW did not increase to the same extent as HCW (7.5 vs. 24.3%), there is a disproportionate amount of additional BW gain required in 2020 compared with 1990 within the feedlot. Therefore, to compare more evenly across year, C-footprint can also be expressed per unit of BW gain. The feedlot contributed 4.78 kg of CO2e/kg of BW gain in 1990, and in 2020 that was decreased by 4.4% to 4.58 kg of CO2e/kg of BW gain. The reduction in CO2e per kilogram of BW gain is supported by the

      IPCC. 2014. Technical summary. Pages 33–107 in AR5 Climate Change 2014: Mitigation of Climate Change. Intergov. Panel Climate Chang.

      indication that global kilograms of CO2e per kilogram of beef has reduced from 1960 to 2010 by about 1.0 kg. It is not surprising that the

      IPCC. 2014. Technical summary. Pages 33–107 in AR5 Climate Change 2014: Mitigation of Climate Change. Intergov. Panel Climate Chang.

      has a slightly greater reduction in CO2e per kilogram than the present study, because it incorporates all segments of the beef production system. In addition, there were fewer growth-promoting technologies available in 1960, causing the decrease from 1960 to 2010 to be more pronounced than that reported in the current model.
      Although it is outside the scope of this study, it should be noted that overall cattle age at slaughter has decreased between 2001 and 2016 despite greater DOF (
      • Lawrence T.E.
      • Whatley J.D.
      • Montgomery T.H.
      • Perino L.J.
      A comparison of the USDA ossification-based maturity system to a system based on dentition..
      ;
      • Eastwood L.C.
      • Boykin C.A.
      • Harris M.K.
      • Arnold A.N.
      • Hale D.S.
      • Kerth C.R.
      • Griffin D.B.
      • Savell J.W.
      • Belk K.E.
      • Woerner D.R.
      • Hasty J.D.
      • Delmore Jr., J.R.J.
      • Martin J.N.
      • Lawrence T.E.
      • McEvers T.J.
      • VanOverbeke D.L.
      • Mafi G.G.
      • Pfeiffer M.M.
      • Schmidt T.B.
      • Maddock R.J.
      • Johnson D.D.
      • Carr C.C.
      • Scheffler J.M.
      • Pringle T.D.
      • Stelzleni A.M.
      National Beef Quality Audit-2016: Transportation, mobility, and harvest-floor assessments of targeted characteristics that affect quality and value of cattle, carcasses, and by-products..
      ). Dentition analysis is the most accurate demonstration of the reduction in animal age. The earliest record of dentition data in the United States was in 2001 (
      • Lawrence T.E.
      • Whatley J.D.
      • Montgomery T.H.
      • Perino L.J.
      A comparison of the USDA ossification-based maturity system to a system based on dentition..
      ), where it was observed that 75.4% of cattle had no permanent incisors at slaughter. More recently, in the 2016 National Beef Quality Audit,
      • Eastwood L.C.
      • Boykin C.A.
      • Harris M.K.
      • Arnold A.N.
      • Hale D.S.
      • Kerth C.R.
      • Griffin D.B.
      • Savell J.W.
      • Belk K.E.
      • Woerner D.R.
      • Hasty J.D.
      • Delmore Jr., J.R.J.
      • Martin J.N.
      • Lawrence T.E.
      • McEvers T.J.
      • VanOverbeke D.L.
      • Mafi G.G.
      • Pfeiffer M.M.
      • Schmidt T.B.
      • Maddock R.J.
      • Johnson D.D.
      • Carr C.C.
      • Scheffler J.M.
      • Pringle T.D.
      • Stelzleni A.M.
      National Beef Quality Audit-2016: Transportation, mobility, and harvest-floor assessments of targeted characteristics that affect quality and value of cattle, carcasses, and by-products..
      reported that 80.5% of cattle had no permanent incisors at slaughter. As such, if cattle are slaughtered at a younger age, total C-footprint per animal will likely be reduced over the total cattle life cycle.
      Furthermore, as cattle spend more time in the feedlot, the amount of time spent in the cow-calf and stocker segments of the beef industry are reduced as a proportion of their total life. According to
      • Stackhouse-Lawson K.R.
      • Rotz C.A.
      • Oltjen J.W.
      • Mitloehner F.M.
      Carbon footprint and ammonia emissions of California beef production systems..
      , the feedlot produced 3.1 and 1.56 times less CO2e per kilogram of BW gain than the cow-calf and stocker operations, respectively. Cattle spent 212 d in the cow-calf phase, 182 d in the stocker phase, and 121 d in the feedlot.
      • Stackhouse-Lawson K.R.
      • Rotz C.A.
      • Oltjen J.W.
      • Mitloehner F.M.
      Carbon footprint and ammonia emissions of California beef production systems..
      indicated that if the stocker operation was removed, there is a potential decrease in total CO2e of 6.5% over the entire beef production system. In addition, more growth-promoting technologies can be applied in the feedlot compared with the cow-calf operation, allowing for greater reductions in CO2e.
      When this model is extrapolated to the 33.24 million cattle slaughtered in 1990 (

      USDA-ERS. 2020. Meat Statistics: Meat Production, Slaughter, Dressed Weights, and Cold Storage with History. USDA Econ. Res. Serv.

      ), feedlots produced a total of 29.88 billion kilograms of CO2e in 1990. In contrast, in 2020, 1.4% fewer cattle (

      USDA-ERS. 2020. Meat Statistics: Meat Production, Slaughter, Dressed Weights, and Cold Storage with History. USDA Econ. Res. Serv.

      ) were slaughtered but produced a total of 43.16 billion kilograms of CO2e. As cattle spend a greater proportion of their life in the feedlot, more of their lifetime emissions will be assigned to that segment of the industry. However, because cattle produced in 2020 had 47.5% more BW gain and 24.3% more HCW, the feedlot segment has reduced the quantity of emissions that contribute to GWP compared with the amount of beef produced, as evidenced by a 4.4% decrease in CO2e per kilogram of BW gain.

      APPLICATIONS

      Based on the estimates reported in this study, incorporating the use of growth-promoting technologies into the beef feedlot production system improves performance of finishing cattle. Although concerns regarding the use of products such as implants, ionophores, and βAA have become prevalent in recent years, previous research indicates that these conventional management practices improve feedlot cattle production (
      • Maxwell C.L.
      • Krehbiel C.R.
      • Wilson B.K.
      • Johnson B.T.
      • Bernhard B.C.
      • O’Neill C.F.
      • VanOverbeke D.L.
      • Mafi G.G.
      • Step D.L.
      • Richards C.J.
      Effects of beef production system on animal performance and carcass characteristics..
      ) and decrease the environmental impact (
      • Stackhouse K.R.
      • Rotz C.A.
      • Oltjen J.W.
      • Mitloehner F.M.
      Growth-promoting technologies decrease the carbon footprint, ammonia emissions, and costs of California beef production systems..
      ). The present study also suggests that these management strategies decrease the C-footprint of beef feedlots. From 1990 to 2020 feedlots have increased BW gain more than the increase in kilograms of CO2e, resulting in a 4.4% decrease of CO2e per kilogram of BW gain. The disproportionate increase in BW gain compared with CO2e indicates that feedlots are decreasing the environmental impact intensity and improving efficiency, while continuing to meet the protein needs of a growing population. Therefore, current management practices that include the use of growth-promoting technologies in combination with improved production practices have increased performance of beef cattle, reduced the environmental impact per kilogram of BW gain, and positively affected the sustainability of beef production over the past 30 yr.

      ACKNOWLEDGMENTS

      This study was funded by the Beef Checkoff. For more information, contact Myriah Johnson, senior director of the National Cattlemen’s Beef Association, which contracts to manage sustainability research for the Beef Checkoff Program, at mdjohnson@beef.org. The authors thank Myriah Johnson and Jessica Soule for their input on this manuscript.

      LITERATURE CITED

        • Abney C.S.
        • Vasconcelos J.T.
        • McMeniman J.P.
        • Keyser S.A.
        • Wilson K.R.
        • Vogel G.J.
        • Galyean M.L.
        Effects of ractopamine hydrochloride on performance, rate and variation in feed intake, and acid-base balance in feedlot cattle..
        J. Anim. Sci. 2007; 85: 3090-3098
        • Adom F.
        • Maes A.
        • Workman C.
        • Clayton-Nierderman Z.
        • Thoma G.
        • Shonnard D.
        Regional carbon footprint analysis of dairy feeds for milk production in the USA..
        Int. J. Life Cycle Assess. 2012; 17: 520-534
        • Bauer M.L.
        • Herold D.W.
        • Britton R.A.
        • Stock R.A.
        • Klopfenstein T.J.
        • Yates D.A.
        Efficacy of laidlomycin propionate to reduce ruminal acidosis in cattle..
        J. Anim. Sci. 1995; 73: 3445-3454
        • Beck P.
        • Hess T.
        • Hubbell D.
        • Hufstedler G.D.
        • Fieser B.
        • Caldwell J.
        Additive effects of growth promoting technologies on performance of grazing steers and economics of the wheat pasture enterprise..
        J. Anim. Sci. 2014; 92: 1219-1227
        • Birkelo C.P.
        Pharmaceuticals, direct-fed microbials, and enzymes for enhancing growth and feed efficiency of beef cattle..
        Vet. Clin. North Am. Food Anim. Pract. 2003; 19: 599-624
        • Bothast R.
        • Schlicher M.
        Biotechnological processes for conversion of corn into ethanol..
        Appl. Microbiol. Biotechnol. 2005; 67: 19-25
      1. Bouffault, J., and J. Willemart. 1983. Anabolic activity of trenbolone acetate alone or in association with estrogens. Pages 155–179 in Anabolics in Animal Production. E. Meissonnier, ed. Office Int. Epizooties.

        • Bryant T.C.
        • Engle T.E.
        • Galyean M.L.
        • Wagner J.J.
        • Tatum J.D.
        • Anthony R.V.
        • Laudert S.B.
        Effects of ractopamine and trenbolone acetate implants with or without estradiol on growth performance, carcass characteristics, adipogenic enzyme activity, and blood metabolites in feedlot steers and heifers..
        J. Anim. Sci. 2010; 88: 4102-4119
        • Budde A.M.
        • Sellins K.
        • Lloyd K.E.
        • Wagner J.J.
        • Heldt J.S.
        • Spears J.W.
        • Engle T.E.
        Effect of zinc source and concentration and chromium supplementation on performance and carcass characteristics in feedlot steers..
        J. Anim. Sci. 2019; 97: 1286-1295
        • Buttrey E.K.
        • Cole N.A.
        • Jenkins K.H.
        • Meyer B.E.
        • McCollum III, F.T.
        • Preece S.L.M.
        • Auvermann B.W.
        • Heflin K.R.
        • MacDonald J.C.
        Effects of twenty percent corn wet distillers grains plus solubles in steam-flaked and dry-rolled corn-based finishing diets on heifer performance, carcass characteristics, and manure characteristics..
        J. Anim. Sci. 2012; 90: 5086-5098
        • Buttrey E.K.
        • Jenkins K.H.
        • Lewis J.B.
        • Smith S.B.
        • Miller R.K.
        • Lawrence T.E.
        • McCollum III, F.T.
        • Pinedo P.J.
        • Cole N.A.
        • MacDonald J.C.
        Effects of 35% corn wet distillers grains plus solubles in steam-flaked and dry-rolled corn-based finishing diets on animal performance, carcass characteristics, beef fatty acid composition, and sensory attributes.
        J. Anim. Sci. 2013; 91: 1850-1865
        • Chen M.
        • Wolin M.J.
        Effect of monensin and lasalocid-sodium on the growth of methanogenic and rumen saccharolytic bacteria..
        Appl. Environ. Microbiol. 1979; 38: 72-77
        • Cheng K.J.
        • McAllister T.A.
        • Popp J.D.
        • Hristov A.N.
        • Mir Z.
        • Shin H.T.
        A review of bloat in feedlot cattle..
        J. Anim. Sci. 1998; 76: 299-308
        • Cole N.A.
        • Meyer B.E.
        • Parker D.B.
        • Neel J.
        • Turner K.E.
        • Northup B.K.
        • Jennings T.
        • Jennings J.S.
        Effects of diet quality on energy metabolism and methane production by beef steers fed a warm-season grass-based hay diet..
        Appl. Anim. Sci. 2020; 36 (a): 652-667
        • Cole N.A.
        • Parker D.B.
        • Brown M.S.
        • Jennings J.S.
        • Hales K.E.
        • Gunter S.A.
        Effects of steam flaking on the carbon-footprint of finishing beef cattle..
        Transl. Anim. Sci. 2020; 4 (b): S84-S89
        • da Silva J.C.B.
        • Cole N.A.
        • Ponce C.H.
        • Smith D.R.
        • Greene L.W.
        • Schuster G.
        • Brown M.S.
        Effects of supplemental fat concentration on feeding logistics, animal performance, and nutrient losses of heifers fed finishing diets based on steam-flaked corn and sorghum-based distiller’s grains..
        J. Anim. Sci. 2019; 97: 2583-2597
        • Drehmel O.R.
        • Brown-Brandl T.M.
        • Judy J.V.
        • Fernando S.C.
        • Miller P.S.
        • Hales K.E.
        • Kononoff P.J.
        The influence of fat and hemicellulose on methane production and energy utilization in lactating Jersey cattle..
        J. Dairy Sci. 2018; 101: 7892-7906
        • Duckett S.K.
        • Andrae J.G.
        Implant strategies in an integrated beef production system..
        J. Anim. Sci. 2001; 79: E110-E117
        • Duffield T.F.
        • Merrill J.K.
        • Bagg R.N.
        Meta-analysis of the effects of monensin in beef cattle on feed efficiency, body weight gain, and dry matter intake..
        J. Anim. Sci. 2012; 90: 4583-4592
        • Eastwood L.C.
        • Boykin C.A.
        • Harris M.K.
        • Arnold A.N.
        • Hale D.S.
        • Kerth C.R.
        • Griffin D.B.
        • Savell J.W.
        • Belk K.E.
        • Woerner D.R.
        • Hasty J.D.
        • Delmore Jr., J.R.J.
        • Martin J.N.
        • Lawrence T.E.
        • McEvers T.J.
        • VanOverbeke D.L.
        • Mafi G.G.
        • Pfeiffer M.M.
        • Schmidt T.B.
        • Maddock R.J.
        • Johnson D.D.
        • Carr C.C.
        • Scheffler J.M.
        • Pringle T.D.
        • Stelzleni A.M.
        National Beef Quality Audit-2016: Transportation, mobility, and harvest-floor assessments of targeted characteristics that affect quality and value of cattle, carcasses, and by-products..
        Transl. Anim. Sci. 2017; 1: 229-238
        • Erickson G.E.
        • Milton C.T.
        • Fanning K.C.
        • Cooper R.J.
        • Swingle R.S.
        • Parrott J.C.
        • Vogel G.
        • Klopfenstein T.J.
        Interaction between bunk management and monensin concentration on finishing performance, feeding behavior, and ruminal metabolism during an acidosis challenge with feedlot cattle..
        J. Anim. Sci. 2003; 81: 2869-2879
      2. FOIA (Freedom of Information Act). 1987. Finaplix. US Food Drug Admin.

        • Fox D.G.
        • Sniffen C.J.
        • O’Connor J.D.
        • Russell J.B.
        • Van Soest P.J.
        A net carbohydrate and protein system for evaluating cattle diets: III. Cattle requirements and diet adequacy..
        J. Anim. Sci. 1992; 70: 3578-3596
        • Galyean M.L.
        Protein levels in beef cattle finishing diets: Industry application, university research, and systems results..
        J. Anim. Sci. 1996; 74: 2860-2870
        • Galyean M.L.
        • Malcolm K.J.
        • Duff G.C.
        Performance of feedlot steers fed diets containing laidlomycin propionate or monensin plus tylosin, and effects of laidlomycin propionate concentration on intake patterns and ruminal fermentation in beef steers during adaptation to a high-concentrate diet..
        J. Anim. Sci. 1992; 70: 2950-2958
        • Genther-Schroeder O.N.
        • Branine M.E.
        • Hansen S.L.
        Effects of increasing supplemental dietary Zn concentration on growth performance and carcass characteristics in finishing steers fed ractopamine hydrochloride..
        J. Anim. Sci. 2018; 96: 1903-1913
        • Goodrich R.D.
        • Garrett J.E.
        • Gast D.R.
        • Kirick M.A.
        • Larson D.A.
        • Meiske J.C.
        Influence of monensin on the performance of cattle..
        J. Anim. Sci. 1984; 58: 1484-1498
        • Gruber S.L.
        • Tatum J.D.
        • Engle T.E.
        • Mitchell M.A.
        • Laudert S.B.
        • Schroeder A.L.
        • Platter W.J.
        Effects of ractopamine supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type..
        J. Anim. Sci. 2007; 85: 1809-1815
        • Hales K.E.
        • Brown-Brandl T.M.
        • Freetly H.C.
        Effects of decreased dietary roughage concentration on energy metabolism and nutrient balance in finishing beef cattle..
        J. Anim. Sci. 2014; 92: 264-271
        • Ham G.A.
        • Stock R.A.
        • Klopfenstein T.J.
        • Larson E.M.
        • Shain D.H.
        • Huffman R.P.
        Wet corn distillers byproducts compared with dried corn distillers grains with solubles as a source of protein and energy for ruminants..
        J. Anim. Sci. 1994; 72: 3246-3257
        • Hemphill C.N.
        • Wickersham T.A.
        • Sawyer J.E.
        • Brown-Brandl T.M.
        • Freetly H.C.
        • Hales K.E.
        Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance..
        J. Anim. Sci. 2018; 96: 1171-1180
        • Hünerberg M.
        • Little S.M.
        • Beauchemin K.A.
        • McGinn S.M.
        • O’Connor D.
        • Okine E.K.
        • Harstad O.M.
        • Kröbel R.
        • McAllister T.A.
        Feeding high concentrations of corn dried distillers’ grains decreases methane, but increases nitrous oxide emissions from beef cattle production..
        Agric. Syst. 2014; 127: 19-27
        • Hussein H.S.
        • Berger L.L.
        Effects of feed intake and dietary level of wet corn gluten feed on feedlot performance, digestibility of nutrients, and carcass characteristics of growing-finishing beef heifers..
        J. Anim. Sci. 1995; 73: 3246-3252
      3. IPCC (Intergovernmental Panel on Climate Change). 2006. Guidelines for national greenhouse gas inventories. Vol. 4. Agriculture, Forestry and Other Land Use. Accessed Jul. 15, 2021. http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol1.html.

      4. IPCC. 2014. Technical summary. Pages 33–107 in AR5 Climate Change 2014: Mitigation of Climate Change. Intergov. Panel Climate Chang.

      5. IPCC. 2019. Chapter 10. Emissions from livestock and manure management. Pages 10.1–10.87 in 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergov. Panel Climate Chang.

        • Kim S.
        • Dale B.E.
        Allocation procedure in ethanol production system from corn grain i. System expansion..
        Int. J. Life Cycle Assess. 2002; 7: 237
        • Klopfenstein T.J.
        • Erickson G.E.
        • Bremer V.R.
        Board-Invited Review: Use of distillers by-products in the beef cattle feeding industry..
        J. Anim. Sci. 2008; 86: 1223-1231
        • Krehbiel C.
        • Stock R.
        • Herold D.
        • Shain D.
        • Ham G.
        • Carulla J.
        Feeding wet corn gluten feed to reduce subacute acidosis in cattle..
        J. Anim. Sci. 1995; 73 (a): 2931-2939
        • Krehbiel C.R.
        • Stock R.A.
        • Shain D.H.
        • Richards C.J.
        • Ham G.A.
        • McCoy R.A.
        • Klopfenstein T.J.
        • Britton R.A.
        • Huffman R.P.
        Effect of level and type of fat on subacute acidosis in cattle fed dry-rolled corn finishing diets..
        J. Anim. Sci. 1995; 73 (b): 2438-2446
      6. Kuhl, G. 1997. Kansas State University Focus on Feedlots. Accessed Sep. 18, 2021. https://www.asi.k-state.edu/about/newsletters/focus-on-feedlots/monthly-reports.html.

        • Ladely S.R.
        • Stock R.A.
        • Goedeken F.K.
        • Huffman R.P.
        Effect of corn hybrid and grain processing method on rate of starch disappearance and performance of finishing cattle..
        J. Anim. Sci. 1995; 73: 360-364
        • Lawrence T.E.
        • Whatley J.D.
        • Montgomery T.H.
        • Perino L.J.
        A comparison of the USDA ossification-based maturity system to a system based on dentition..
        J. Anim. Sci. 2001; 79: 1683-1690
        • Lewis J.M.
        • Klopfenstein T.J.
        • Stock R.A.
        Effects of rate of gain during winter on subsequent grazing and finishing performance..
        J. Anim. Sci. 1990; 68: 2525-2529
        • López-Carlos M.A.
        • Ramírez R.G.
        • Aguilera-Soto J.I.
        • Aréchiga C.F.
        • Méndez-Llorente F.
        • Rodríguez H.
        • Silva J.M.
        Effect of ractopamine hydrochloride and zilpaterol hydrochloride on growth, diet digestibility, intake and carcass characteristics of feedlot lambs..
        Livest. Sci. 2010; 131: 23-30
        • Ludden P.A.
        • Cecava M.J.
        • Hendrix K.S.
        The value of soybean hulls as a replacement for corn in beef cattle diets formulated with or without added fat..
        J. Anim. Sci. 1995; 73: 2706-2711
        • Lynch G.S.
        • Ryall J.G.
        Role of β-adrenoceptor signaling in skeletal muscle: Implications for muscle wasting and disease..
        Physiol. Rev. 2008; 88: 729-767
      7. MacDonald, J., N. A. Cole, J. Osterstock, and K. E. Hales. 2009. Technology in the Industry—Where Would We, and the World, Be Without It? Planis Nutr. Counc.

        • Maxwell C.L.
        • Krehbiel C.R.
        • Wilson B.K.
        • Johnson B.T.
        • Bernhard B.C.
        • O’Neill C.F.
        • VanOverbeke D.L.
        • Mafi G.G.
        • Step D.L.
        • Richards C.J.
        Effects of beef production system on animal performance and carcass characteristics..
        J. Anim. Sci. 2014; 92: 5727-5738
        • McGinn S.M.
        • Beauchemin K.A.
        • Coates T.
        • Colombatto D.
        Methane emissions from beef cattle: Effects of monensin, sunflower oil, enzymes, yeast, and fumaric acid..
        J. Anim. Sci. 2004; 82: 3346-3356
        • McGuffey R.K.
        • Richardson L.F.
        • Wilkinson J.I.D.
        Ionophores for dairy cattle: Current status and future outlook..
        J. Dairy Sci. 2001; 84: E194-E203
        • Müller H.C.
        • Van Bibber-Krueger C.L.
        • Ogunrinu O.J.
        • Amachawadi R.G.
        • Scott H.M.
        • Drouillard J.S.
        Effects of intermittent feeding of tylosin phosphate during the finishing period on feedlot performance, carcass characteristics, antimicrobial resistance, and incidence and severity of liver abscesses in steers..
        J. Anim. Sci. 2018; 96: 2877-2885
      8. NASEM (National Academies of Sciences, Engineering, and Medicine). 2000. Nutrient Requirements of Beef Cattle. Update 2000. Natl. Acad. Press.

      9. NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Nutrient Requirements of Beef Cattle. 8th ed. Natl. Acad. Press.

        • Parker D.B.
        • Meyer B.
        • Jennings T.
        • Jennings J.
        • Dougherty H.
        • Cole N.A.
        • Casey K.
        Enteric nitrous oxide emissions from beef cattle..
        Prof. Anim. Sci. 2018; 34: 594-607
        • Ponce C.H.
        • Cole N.A.
        • Sawyer J.
        • da Silva J.C.B.
        • Smith D.R.
        • Maxwell C.
        • Brown M.S.
        Effects of wet corn distiller’s grains with solubles and nonprotein nitrogen on feeding efficiency, growth performance, carcass characteristics, and nutrient losses of yearling steers..
        J. Anim. Sci. 2019; 97: 2609-2630
      10. Powers, W., B. Auvermann, N. A. Cole, C. Gooch, R. Grant, J. Hatfield, P. Hunt, K. Johnson, A. Leytem, W. Liao, and J. M. Powell. 2014. Chapter 5: Quantifying greenhouse gas sources and sinks in animal production systems. Pages 5.5–5.160 in Quantifying Greenhouse Gas Fluxes in Agriculture and Forestry: Methods for Entity-Scale Inventory. Tech. Bull. No. 1939. M. Eve, D. Pape, M. Flugge, R. Steele, D. Man, M. Riley-Gilbert, and S. Biggar, ed. Office Chief Econ., USDA.

        • Quinn M.J.
        • Reinhardt C.D.
        • Loe E.R.
        • Depenbusch B.E.
        • Corrigan M.E.
        • May M.L.
        • Drouillard J.S.
        The effects of ractopamine-hydrogen chloride (Optaflexx) on performance, carcass characteristics, and meat quality of finishing feedlot heifers..
        J. Anim. Sci. 2008; 86: 902-908
        • Quinn M.J.
        • Walter L.J.
        • Swingle R.S.
        • Defoor P.J.
        • Harper L.B.
        • Lawrence T.E.
        Comparison of the effects of Actogain or Optaflexx on finishing feedlot steer performance and carcass characteristics..
        Prof. Anim. Sci. 2016; 32: 455-460
        • Ranga Niroshan Appuhamy J.A.D.
        • Strathe A.B.
        • Jayasundara S.
        • Wagner-Riddle C.
        • Dijkstra J.
        • France J.
        • Kebreab E.
        Anti-methanogenic effects of monensin in dairy and beef cattle: A meta-analysis..
        J. Dairy Sci. 2013; 96: 5161-5173
        • Raun A.
        • Preston R.
        History of diethylstilbestrol use in cattle..
        J. Anim. Sci. 2002; 80: 1-7
        • Reinhardt C.D.
        • Wagner J.J.
        High-dose anabolic implants are not all the same for growth and carcass traits of feedlot steers: A meta-analysis..
        J. Anim. Sci. 2014; 92: 4711-4718
        • Russell J.B.
        • Strobel H.J.
        Effect of ionophores on ruminal fermentation..
        Appl. Environ. Microbiol. 1989; 55: 1-6
        • Russell J.R.
        • Lundy E.L.
        • Minton N.O.
        • Sexten W.J.
        • Kerley M.S.
        • Hansen S.L.
        Influence of growing phase feed efficiency classification on finishing phase growth performance and carcass characteristics of beef steers fed different diet types..
        J. Anim. Sci. 2016; 94: 58-59
        • 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..
        J. Anim. Sci. 2016; 94: 2648-2663
        • Schlesinger W.H.
        • Amundson R.
        Managing for soil carbon sequestration: Let’s get realistic..
        Glob. Chang. Biol. 2018; 25: 386-389
      11. Schroeder, A. L., D. M. Polser, S. B. Laudert, G. J. Vogel, T. Ripberger, and M. T. Van Koevering. 2004. The effect of Optaflexx on growth performance and carcass traits of steers and heifers. Pages 65–72 in Proc. Southwest Nutr. Manage. Conf., Univ. Arizona, Tucson.

        • Schwandt E.F.
        • Wagner J.J.
        • Engle T.E.
        • Bartle S.J.
        • Thomson D.U.
        • Reinhardt C.D.
        The effects of dry-rolled corn particle size on performance, carcass traits, and starch digestibility in feedlot finishing diets containing wet distiller’s grains..
        J. Anim. Sci. 2016; 94: 1194-1202
        • Searchinger T.
        • Heimlich R.
        • Houghton R.A.
        • Dong F.
        • Elobeid A.
        • Fabiosa J.
        • Tokgoz S.
        • Hayes D.
        • Yu T.-H.
        Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change..
        Science. 2008; 319: 1238-1240
        • Smith S.B.
        • Garcia D.K.
        • Anderson D.B.
        Elevation of a specific mRNA in longissimus muscle of steers fed ractopamine..
        J. Anim. Sci. 1989; 67: 3495-3502
        • Stackhouse K.R.
        • Rotz C.A.
        • Oltjen J.W.
        • Mitloehner F.M.
        Growth-promoting technologies decrease the carbon footprint, ammonia emissions, and costs of California beef production systems..
        J. Anim. Sci. 2012; 90: 4656-4665
        • Stackhouse-Lawson K.R.
        • Calvo M.S.
        • Place S.E.
        • Armitage T.L.
        • Pan Y.
        • Zhao Y.
        • Mitloehner F.M.
        Growth promoting technologies reduce greenhouse gas, alcohol, and ammonia emissions from feedlot cattle..
        J. Anim. Sci. 2013; 91: 5438-5447
        • Stackhouse-Lawson K.R.
        • Rotz C.A.
        • Oltjen J.W.
        • Mitloehner F.M.
        Carbon footprint and ammonia emissions of California beef production systems..
        J. Anim. Sci. 2012; 90: 4641-4655
      12. Steinfeld, H., P. Gerber, T. Wassenaaar, V. Castel, M. Rosales, and C. DeHaan. 2006. Livestock’s Long Shadow: Environmental Issues and Options. Food Agric. Org. United Nations. Accessed Jul. 14, 2021. ftp://ftp.fao.org/docrep/fao/010/a0701e/a0701e00.pdf.

        • Stock R.A.
        • Laudert S.B.
        • Stroup W.W.
        • Larson E.M.
        • Parrott J.C.
        • Britton R.A.
        Effect of monensin and monensin and tylosin combination on feed intake variation of feedlot steers..
        J. Anim. Sci. 1995; 73: 39-44
        • Stokes R.S.
        • Loy D.D.
        • Hansen S.L.
        Effects of increased inclusion of algae meal on finishing steer performance and carcass characteristics..
        J. Anim. Sci. 2016; 94: 687-696
        • Tedeschi L.O.
        Potential environmental benefits of feed additives and other strategies for ruminant production..
        Rev. Bras. Zootec. 2011; 40: 291-309
        • Tedeschi L.O.
        • Fox D.G.
        • Tylutki T.P.
        Potential environmental benefits of ionophores in ruminant diets..
        J. Environ. Qual. 2003; 32: 1591-1602
        • Teixeira P.D.
        • Tekippe J.A.
        • Rodrigues L.M.
        • Ladeira M.M.
        • Pukrop J.R.
        • Kim Y.H.B.
        • Schoonmaker J.P.
        Effect of ruminally protected arginine and lysine supplementation on serum amino acids, performance, and carcass traits of feedlot steers..
        J. Anim. Sci. 2019; 97: 3511-3522
        • Thompson A.J.
        • Smith Z.K.F.
        • Corbin M.J.
        • Harper L.B.
        • Johnson B.J.
        Ionophore strategy affects growth performance and carcass characteristics in feedlot steers..
        J. Anim. Sci. 2016; 94: 5341-5349
        • Todd R.W.
        • Cole N.A.
        • Clark R.N.
        • Flesch T.K.
        • Harper L.A.
        • Baek B.H.
        Ammonia emissions from a beef cattle feedyard on the southern High Plains..
        Atmos. Environ. 2008; 42: 6797-6805
      13. USDA-ERS. 2020. Meat Statistics: Meat Production, Slaughter, Dressed Weights, and Cold Storage with History. USDA Econ. Res. Serv.

      14. USDA-NAHMS. 2013. Trends in Health and Management Practices on US Feedlots, 1994–2011. USDA Natl. Anim. Health Monit. Syst.

        • Van Nevel C.J.
        • Demeyer D.I.
        Effect of monensin on rumen metabolism in vitro..
        Appl. Environ. Microbiol. 1977; 34: 251
      15. Waggoner, J. 2020. Kansas State University Focus on Feedlots. Accessed Sep. 18, 2021. https://www.asi.k-state.edu/about/newsletters/focus-on-feedlots/monthly-reports.html.

        • Warner A.L.
        • Beck P.A.
        • Foote A.P.
        • Pierce K.N.
        • Robison C.A.
        • Hubbell D.S.
        • Wilson B.K.
        Effects of utilizing cotton byproducts in a finishing diet on beef cattle performance, carcass traits, fecal characteristics, and plasma metabolites..
        J. Anim. Sci. 2020; 98 (skaa038)
        • Wellmann K.B.
        • Baggerman J.O.
        • Burson W.C.
        • Smith Z.K.
        • Kim J.
        • Hergenreder J.E.
        • Rounds W.
        • Bernhard B.C.
        • Johnson B.J.
        Effects of zinc propionate supplementation on growth performance, skeletal muscle fiber, and receptor characteristics in beef steers..
        J. Anim. Sci. 2020; 98 (skaa210)
        • Wileman B.W.
        • Thomson D.U.
        • Reinhardt C.D.
        • Renter D.G.
        Analysis of modern technologies commonly used in beef cattle production: Conventional beef production versus nonconventional production using meta-analysis..
        J. Anim. Sci. 2009; 87: 3418-3426
        • Xiong Y.
        • Bartle S.J.
        • Preston R.L.
        Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers..
        J. Anim. Sci. 1991; 69: 1707-1718
        • Zinn R.A.
        Influence of flake density on the comparative feeding value of steam-flaked corn for feedlot cattle..
        J. Anim. Sci. 1990; 68: 767-775
        • Zinn R.A.
        Comparative feeding value of steam-flaked corn and sorghum in finishing diets supplemented with or without sodium bicarbonate..
        J. Anim. Sci. 1991; 69: 905-916