Objective: Wet distillers grains with solubles (WDGS) are a common feed ingredient used in cattle finishing diets. However, the NE values of WDGS have not been clearly delineated, and there may be an interaction between grain processing method and the feeding value of WDGS. This study was conducted to evaluate the relative NE values of WDGS and to evaluate possible associative effects between WDGS and steam -flaked corn (SFC) on energy and nitrogen utilization by finishing beef steers. Materials and Methods: Four British crossbred steers were used in a 4 x 4 Latin square design in which steers were fed 1 of 4 diets: (1) a basal 86% concentrate diet fed a 1x maintenance (B), (2) the basal diet + SFC fed at 1.5x maintenance (B+SFC), (3) the basal diet + WDGS fed at 1.5x maintenance (B+WDGS), and (4) the basal diet + a 50:50 blend of WDGS and SFC fed at 1.5x maintenance (BLEND). Each period of the Latin square was 28 d in length with steers confined to indirect opencircuit respiration chambers the last 5 d of each period. Nutrient digestibility, urinary nutrient excretion, methane and carbon dioxide production, and heat production were determined during the last 5 d of each period. Dietary and ingredient (SFC or WDGS) TDN, DE, ME, and NE values were calculated. Results and Discussion: The digestibility of DM and OM of B+SFC was greater than that of B+WDGS, with the BLEND diet being intermediate. Nitrogen balance was numerically greater for B+WDGS than for B+SFC, with BLEND being intermediate. Digestible energy, ME, and energy retention were greater for B+SFC than for B+WDGS, with BLEND being intermediate. The experimental method used affected the TDN, DE, ME, and NE values of diets, SFC, and WDGS. There were negative associative effects (-1% to -8.0%) between SFC and WDGS for energy values. Actual DE: TDN averaged 4.11 Mcal of DE/kg of TDN, which is less than the 4.4 value used by NASEM (2016). The DE: digestible OM ratio averaged 4.54 Mcal/kg, and the digestible OM: TDN ratio averaged 90.2. Implications and Applications: Our results suggest that within the range of rations fed in this study, the NE values for WDGS by NASEM (2016) may overestimate their relative NE (15%) when fed in diets based on SFC.

Objective: The objective of this study was to determine the effects of degree of steam flaking of corn (SFC) on energy metabolism of finishing cattle fed diets containing wet distillers grains with solubles (WDGS). Materials and Methods: Crossbred steers (n = 4; initial BW = 308 +/- 7.0 kg) were randomly assigned to 4 diets containing 0% or 20% WDGS and corn steam flaked to either 321 or 270 g/L bulk density (26 or 22 lb/bu, respectively) in a 2 x 2 factorial arrangement. Energy metabolism was measured in respiration chambers with a 4 x 4 Latin square design. Results and Discussion: There were no interactions between WDGS concentration and SFC bulk density for nutrient digestion, nitrogen metabolism, or energy metabolism values. Digestibility of OM, NDF, and ether extract were not influenced by the degree of steam flaking of corn. Decreasing bulk density of SFC increased starch digestion, tended to increase the ratio of DE to digestible OM, and numerically decreased the plasma urea-N concentration, but did not significantly affect ME concentration or the DE: TDN ratio. Replacing SFC with 20% WDGS decreased fat digestion but did not affect digestion of other nutrients or dietary energy values. Implications and Applications: Results suggest that increasing the degree of steam flaking of corn to less than 321 g/L does not improve diet digestibility or energy metabolism of cattle fed diets containing 0% or 20% WDGS.

Highlights Nitrous oxide and methane emissions were measured from a commercial beef feedyard following large rainfall events. Nitrous oxide emissions dropped below detection levels for ten days following a 77 mm rainfall event. Daily N 2 O and CH 4 emissions followed a diel pattern, peaking at manure temperatures of 36°C to 38°C. Results will be used to refine empirical models for predicting GHG emissions from open-lot feedyards. Abstract . More than six million beef cattle are fed annually in feedyards on the semiarid Southern Great Plains (SGP). Manure deposited on the open-lot pen surfaces contributes to greenhouse gas (GHG) emissions. Nitrous oxide (N2O) and methane (CH4) are GHGs linked to climate change, and both have global warming potentials greater than carbon dioxide (CO2). Two sampling campaigns were conducted in 2019 to quantify N2O and CH4 emissions from open-lot pen surfaces. The occurrence of large, unforecast rainfall events during both campaigns provided an opportunity to compare GHG emissions from the dry manure before rainfall and from the wetted pen surface for one to two weeks following precipitation. Temporal variability was quantified by continuous sampling using six to eight automated flux chambers, a multiplexer system, and real-time analyzers. Spatial variability was quantified using a recirculating portable chamber on a 5 × 8 grid. Nitrous oxide emissions dropped below detection levels for ten days after the precipitation event. Nitrous oxide emissions were related to nitrification or other aerobic processes. Methane emissions dropped below detection levels for five days after the precipitation event and then increased to pre-rainfall levels by day 8. When present, N2O and CH4 emissions followed a diel pattern, with the highest emissions occurring during the afternoon when manure pack temperatures at the 25 mm depth were 36°C to 38°C and ambient temperatures were 31°C to 32°C. Average CH4 emissions from the feedyard pen surface were 96-fold lower than estimated enteric CH4 emissions. The results of this field research will be used to refine empirical models for predicting annual N2O and CH4 emissions from open-lot beef cattle feedyards on the semiarid SGP. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Nitrous oxide, Rainfall.

Highlights Open-lot beef cattle feedyards are a source of greenhouse gas emissions. Pen surface methane emissions were quantified during the cool and warm seasons. Methane was generated in the lower anaerobic layers of the manure pack. Methane emissions decreased after rainfall due to methane oxidation or blocking of pore space. Pen surface methane emissions accounted for <1% of overall feedyard GHG as CO 2eq . Abstract . Texas is one of the top beef-producing states, where annually more than five million beef cattle are finished in large feedyards on earthen-surfaced pens. Manure deposited on open-lot pen surfaces can contribute to greenhouse gas (GHG) emissions such as methane (CH4). Two week-long sampling campaigns were conducted in April (cool season) and August (warm season) to quantify CH4 emissions from the feedyard pen surface. Emissions were monitored before and after 12.7 mm simulated rainfall events. Temporal and spatial variabilities in emissions were quantified using automated recirculating flux chambers, a multiplexer system, and a real-time CH4 analyzer. During the cool season, mean CH4 flux was 1.09 (SD ±2.39) and 0.12 (±0.25) g animal-1 d-1 before and after rainfall, respectively. During the warm season, mean CH4 flux was 0.65 (±1.01) and 0.26 (±0.44) g animal-1 d-1 before and after rainfall, respectively. This suggested that CH4 was produced in the lower, anaerobic layer of the manure pack and CH4 emissions were inhibited following rainfall, most likely due to microbial oxidation of CH4 in the upper layers through methanotrophy or from slowing of diffusion by blocking the manure pore space. The overall mean pen surface CH4 flux was 0.53 g animal-1 d-1. This flux accounted for a small percentage (<1%) of the overall estimated feedyard GHG emissions expressed as CO2eq. Thus, efforts to mitigate GHG from open-lot beef cattle feedyards in the Texas Panhandle should focus on sources with higher percentages of overall GHG, such as enteric methane, pen surface nitrous oxide, and nitrous oxide from fertilized cropland. Keywords: Beef cattle, Flux chamber, Greenhouse gas, Manure, Methane, Rainfall.

Providing supplements that enhance the efficiency of feed utilization can reduce methane (CH4) emissions from ruminants. Protein supplementation is widely used to increase intake and digestion of low-quality forages, yet little is known about its impact on CH4 emissions. British-cross steers (n = 23; initial body weight [BW] = 344 +/- 33.9 kg) were used in a three-period crossover design to evaluate the effect of protein supplementation to beef cattle consuming low-quality forage on ruminal CH4, metabolic carbon dioxide (CO2) emissions, forage intake, and ruminal fermentation. Steers individually had ad libitum access to low-quality bluestem hay (4.6% crude protein [CP]) and were provided supplemental protein based on (dry matter basis): cottonseed meal (CSM; 0.29% of BW daily; 391 g/d CP), dried distillers grains with solubles (DDGS; 0.41% of BW daily 563 g/d CP), or none (CON). Urea was added to DDGS to match rumen degradable protein provided by CSM. Ruminal CH4 and metabolic CO2 fluxes were obtained 2.4 +/- 0.4 times per steer daily using an automated open-circuit gas quantification system (GreenFeed emission monitoring system; C-Lock Inc., Rapid City, SD). Forage intake increased (P < 0.01) with protein supplementation; however, no difference in forage intake (P = 0.14) was observed between CSM and DDGS treatments. Flux of CO2 (g/d) was greater (P < 0.01) for steers fed CSM and DDGS than for steers fed CON. Steers supplemented with CSM had greater (P < 0.01) CH4 emissions (211 g/d) than DDGS (197 g/d) both of which were greater (P < 0.01) than CON (175 g/d). Methane emissions as a proportion of gross energy intake (GEI) were lowest (P < 0.01) for DDGS (7.66%), intermediate for CSM (8.46%) steers, and greatest for CON (10.53%). Steers fed DDGS also had the lowest (P < 0.01) ruminal acetate:propionate ratio (3.60), whereas CSM (4.89) was intermediate, and CON (5.64) steers were greatest. This study suggests that the common practice of supplementing protein to cattle consuming low-quality forage decreases greenhouse gas emissions per unit of GEI.

Emissions of greenhouse gases (GHG; methane, CH4; nitrous oxide, N2O) from dairy cattle manure contribute to global climate change. The aim of this study was to assess the associative effects of three different levels [0, 4 and 8% wet weight (WW) basis] of condensed tannins (CT; quebracho tannins) and hydrolysable tannins (HT; chestnut tannins) on CH4 and N2O emissions. The dairy manure consisted of a 50:50 volume mixture of fresh feces and dry manure scraped from the surface of an open-lot dairy in the Texas panhandle. Control (0% tannin), 4%, and 8% of CT or HT (w/w) were added to each bucket and homogenized with a hand mixer for 5 min. Aliquots of 220 g (WW) manure, with or without tannins, were placed into 1 L fermentation bottles (n = 3, total of 18 bottles) and incubated at 39o C for 14 days. A second set of 18 fermenters were set up in the same manner for sample collection at 0, 2, 3, 6, and 9 h to discern changes in pH and redox status. There were no differences in redox values with the addition of either tannin type to in vitro fermenters. However, application of CT to dairy manure reduced (P < 0.05-0.01) cumulative CH4 emissions by 68 to 63% at the concentrations of 4 and 8% WW, respectively, compared with the non-tannin control group. Both CT and HT decreased cumulative N2O emissions (P < 0.02). Examination of the emission kinetics revealed a tradeoff (interchange or pollution swapping) between CH4 and N2O emissions when tannins were applied to manure. These results suggested that the inclusion of 4% CT (WW) is a promising technique for reducing CH4 and N2O emissions from excreted dairy manure. Further study is warranted to investigate the effects of feeding CT and HT on manure-derived GHG in dairy systems.

Objective: Our objective was to determine the effects of dietary quality and protein supplementation of a low-quality warm-season grass hay on energy metabolism and methane emissions of beef steers. Materials and Methods: Eight Angus-cross steers were used in a respiration calorimetry study with a replicated 4 x 4 Latin square design. Experimental diets were (1) a low-quality forage-based diet (7.4% CP, 66.6% NDF); (2) a low-quality forage with supplemental cottonseed meal (10.0% CP, 66.3% NDF); (3) a medium-quality forage-based diet (10.5% CP, 65.0% NDF); and 4) a highquality forage-based diet (13.0% CP, 58.4% NDF). Diets were based on bluestem (Bothriochloa ischaemum) hay cut at 2 stages of maturity. Results and Discussion: Organic matter, fiber, energy, and protein digestibility and energy retention increased (P < 0.05) as the quality of the forage-based diets increased. Total methane production was not affected by diet, but methane production per unit of digested OM or energy retention decreased (P < 0.05) with increased diet quality. Protein supplementation of the low-quality grass hay increased (P < 0.05) DM, fiber, energy, and protein digestion but did not affect methane production. Methane production per unit of energy and protein retention decreased (P < 0.05) with protein supplementation. Enteric nitrous oxide emissions were minor and not affected by diet. An automated head chamber system gave average emission results similar to respiration chambers. Implications and Applications: Results demonstrate that protein supplementation of low-quality forage or increasing the quality of forage-based diets will potentially decrease the carbon-footprint of beef production.

HighlightsNitrous oxide is a greenhouse gas emitted from feedyard pen surfaces.Experiments were conducted to quantify nitrous oxide emissions from precipitation, urine, and feces.Nitrous oxide emissions from urine were about 30% of those from equal amounts of precipitation.Regression equations were developed for empirical modeling of emissions.Abstract. The amount of moisture deposited annually as urine (~320 mm) and feces (~95 mm) on typical semi-arid Texas beef cattle feedyard pens is considerable compared to the regional 470 mm mean annual precipitation. Precipitation is a primary factor affecting nitrous oxide (N2O) emissions from manure, but specific effects of urine and feces deposition are unknown. The objectives of this research were to (1) quantify N2O emissions following precipitation, urine, and feces deposition on a dry feedyard manure surface, and (2) develop equations for future empirical modeling of these emissions. Four experiments (Exp.) were conducted using recirculating flux chambers to quantify N2O emissions. Exp. 1 had treatments (TRT) of water (W), artificial urine (AU), and two urines collected from beef cattle fed high-quality forage (FU) or corn-based concentrate (CU). Exp. 2 had TRT of W, AU, and two feces levels (Fx1 and Fx2). In Exp. 3, N2O emissions were quantified from fresh feces pats. In Exp. 4, the effect of rainfall pH on N2O emissions was evaluated. Results from Exp. 1 showed that the W TRT had the highest mean cumulative N2O emission, while AU, FU, and CU ranged from 31.0% to 70.0% of W on an equal volume-applied basis. There was little correlation between N2O emissions and urine or water nitrogen (N) content. In Exp. 2, W again had the highest cumulative N2O. Cumulative N2O emissions expressed per unit of water added were 29.0, 3.8, 4.5, and 5.1 mg N kg-1 water added for W, AU, Fx1, and Fx2, respectively. In Exp. 3, fresh feces pats emitted no direct N2O, but N2O originated from the dry manure beneath the feces pat due to wetting. In Exp. 4, the highest N2O emissions occurred at pH 5 and pH 8, with lower emissions at pH 6 and pH 7. This research has shown that the addition of moisture to the pen surface from urine and feces contributes considerably to N2O emissions as compared to precipitation alone. The following recommendations were developed for future empirical modeling purposes: (1) N2O emissions from urine should be calculated as 32.7% of those emissions from the equivalent mass deposition of water, and (2) N2O emissions resulting from the mass of water in feces should be calculated as 15.6% of those emissions from the equivalent mass deposition of water. Keywords: Beef cattle, Greenhouse gas, Manure, Nitrous oxide, Urine, Precipitation.

Nitrous oxide (N2O) is a greenhouse gas with a higher global warming potential than carbon dioxide (CO2) or methane (CH4). The objectives of this research were to quantify enteric N2O emissions from beef cattle and determine effects of dietary nitrate (NO3) concentrations. Experiments consisted of one in vitro incubation trial and 2 live animal (LA) trials. During the in vitro trial, gas was collected from 4 forage-based and 5 corn-based diets. During the LA trials, emissions were monitored from steers in respiration chambers. In LA trial 1, 5 measurements of 256 to 720 min were conducted on a single steer within a 48-h period. In LA trial 2, measurements were conducted on 4 steers in the absence of manure. Highest in vitro N2O production was from diets containing added NO3 or alfalfa. In vitro N2O increased with dietary NO3 concentrations (r2 = 0.99), with little correlation to dietary CP (r2 = 0.17). Added NO3 decreased CH4 emissions. Mean N2O emission rates (±SD) from the LA trials were 6.93 ± 2.99 mg of N2O∙kg−1 of DMI in trial 1 and 2.20 ± 0.10 mg of N2O∙kg−1 of DMI in trial 2. Mean enteric N2O emissions accounted for 0.35% (LA trial 1) and 0.12% (LA trial 2) of CO2 equivalents. Enteric N2O emission rates were 6 to 40 times lower than values cited in earlier publications. Enteric N2O emission rates were also 58 to 108 times lower than manure emissions. Therefore, efforts to reduce greenhouse gas emissions from beef cattle should focus on enteric CH4 and manure N2O as opposed to enteric N2O.

Alkali treatment has been used to increase the digestibility of low-quality, fibrous crop residues. However, alkali treatment of the fiber fraction in distillers grains has only briefly been explored. Six ruminally cannulated steers (444 ± 4.0 kg of BW) were used to evaluate the effects of treating sorghum wet distillers grains plus solubles (SWDGS) with calcium hydroxide (CH) in finishing diets. Treatment diets were based on steam-flaked corn and included (1) 30% corn wet distillers grains plus solubles (CDG), (2) 30% SWDGS (SDG), or (3) 30% SWDGS treated with 2.27% CH (SDG-CH). Data were analyzed as a replicated Latin square with 3 dietary treatments and 3 periods using the MIXED procedure of SAS with animal within square as the experimental unit. No differences (P = 0.47) in DMI were observed. Steers consuming CDG had the greatest (P < 0.01) total ruminal VFA concentration, followed by SDG-CH, with SDG having the least. Steers consuming SDG had the greatest (P < 0.01) ruminal pH, followed by SDG-CH and then by CDG. Steers consuming SDG had the greatest (P < 0.01) ruminal acetate:propionate ratio, followed by SDG-CH, with CDG having the least. Steers consuming SDG-CH tended (P = 0.07) to have a greater apparent total-tract digestibility of NDF. No differences (P ≥ 0.15) were observed in apparent total-tract digestibility of DM, OM, ADF, starch, or N. Treating SWDGS with CH increased the digestibility of fiber compared with untreated SWDGS in finishing diets.

The increased use of by-products in finishing diets for cattle leads to diets that contain greater concentrations of crude protein (CP) and metabolizable protein (MP) than required. The hypothesis was that excess dietary CP and MP would increase maintenance energy requirements because of the energy costs of removing excess N as urea in urine. To evaluate the potential efficiency lost, two experiments were performed to determine the effects of feeding excess CP and MP to calves fed a finishing diet at 1 × maintenance energy intake (Exp. 1) and at 2 × maintenance intake (Exp. 2). In each experiment, eight crossbred Angus-based steers were assigned to two dietary treatments in a switchback design with three periods. Treatments were steam-flaked corn-based finishing diets with two dietary protein concentrations, 13.8% CP/9.63% MP (CON) or 19.5% CP/14.14% MP (dry matter basis; ECP), containing corn gluten meal to reflect a diet with excess CP and MP from corn by-products. Each period was 27 d in length with a 19-d dietary adaptation period in outdoor individual pens followed by a 4-d sample collection in one of four open circuit respiration chambers, 2-d fast in outdoor pen, and 2-d fast in one of four respiration chambers. Energy metabolism, diet digestibility, carbon (C) and nitrogen (N) balance, oxygen consumption, and carbon dioxide and methane production were measured. At both levels of intake, digestible energy as a proportion of gross energy (GE) tended to be greater (P < 0.06) in ECP than in CON steers. Metabolizable energy (ME) as a proportion of GE tended to be greater (P = 0.08) in the ECP steers than in the CON steers at 2 × maintenance intake. At 1 × and 2 × maintenance intake, urinary N excretion (g/d) was greater (P < 0.01) in the ECP steers than the CON steers. Heat production as a proportion of ME intake at 1 × maintenance tended (P = 0.06) to be greater for CON than for ECP (90.9% vs. 87.0% for CON and ECP, respectively); however, at 2 × maintenance energy intake, it was not different (63.9% vs. 63.8%, respectively). At 1 × maintenance intake, fasting heat production (FHP) was similar (P = 0.45) for both treatments, whereas at 2 × maintenance intake, FHP tended to be greater (P = 0.09) by 6% in ECP than in CON steers. Maintenance energy requirements estimated from linear and quadratic regression of energy retention on ME intake were 4% to 6% greater for ECP than for CON. Results of these studies suggest that feeding excess CP and MP from a protein source that is high in ruminally undegradable protein and low in protein quality will increase maintenance energy requirements of finishing steers.

Roughage is fed in finishing diets to promote ruminal health and decrease digestive upset, but the inclusion rate is limited because of the cost per unit of energy and feed management issues. Rumination behavior of cattle may be a means to standardize roughage in beef cattle finishing diets, and increasing the particle size of roughage could modulate the ruminal environment and aid in maintaining ruminal pH. Therefore, this experiment was conducted to determine the effects of corn stalk (CS) inclusion rate and particle size in finishing diets on digestibility, rumination, and ruminal fermentation characteristics of beef steers. Four ruminally cannulated steers were used in a 4 × 4 Latin square experiment. Treatments were arranged as a 2 × 2 factorial with treatments consisting of 5% inclusion of a short-grind roughage (5SG), 10% inclusion of a short-grind roughage (10SG), 5% inclusion of a long-grind roughage (5LG), and 10% inclusion of a long-grind roughage (10LG). Differences in particle size were obtained by grinding corn stalks once (LG) or twice (SG) using a commercial tub grinder equipped with a 7.6-cm screen and quantified using the Penn State Particle Separator (PSPS) to estimate physically effective NDF (peNDF). Each period included 14 d for adaptation and 4 d for diet, fecal, and ruminal fluid collections. Animals were outfitted with rumination monitoring collars to continuously measure rumination activity. The 10LG treatment had a greater ( < 0.01) percentage of large particles (retained on the top 3 sieves of the PSPS) compared to the other treatments. This resulted in a greater ( < 0.01) percentage of estimated peNDF for the 10LG diet compared to the others. Feeding diets containing 5% roughage tended to increase ( ≤ 0.09) DM, NDF, and starch total tract digestibility compared to diets containing 10% roughage. Cattle consuming LG treatments had greater ( < 0.01) rumination time and greater ( < 0.01) ruminal pH than cattle consuming diets containing SG roughage. Cattle receiving the 5% inclusion rate of roughage tended to have greater ( = 0.09) time (h/d) under a ruminal pH of 5.6 and a larger ( = 0.03) area under the threshold compared to cattle receiving the 10% roughage treatments. Overall, feeding a lower inclusion of roughage with a larger particle size may stimulate rumination and aid in ruminal buffering similar to that of a higher inclusion of roughage with a smaller particle size, without negatively impacting digestibility and fermentation.

Nitrous oxide (N2O) emission rates have traditionally been measured using non-flow-through (NFT), nonsteady-state (NSS) chambers, which rely on measuring the increase in N2O concentration in the sealed chamber headspace over time. These flux measurements are very labor-and time-intensive, requiring three to four gas samples collected over a 30 to 60 min period, followed by laboratory N2O measurement with a gas chromatograph (GC) and subsequent flux rate calculation. The objective of this research was to develop and evaluate improved, real-time flux chamber designs that rapidly quantify N2O emissions from manure and soil. The first chamber system consisted of six square 0.95 m(2) chamber pans. The chamber pans were mounted on a rail system to facilitate controlled indoor/outdoor laboratory research at a pilot scale. An aluminum lid was moved among the chamber pans. A second portable chamber system with a circular footprint (0.49 m internal dia.) was designed for use in field measurements. With both systems, N2O concentrations were measured each second with 0.1 ppb resolution by recirculating sample air through a real-time continuous N2O analyzer with return flow into the recirculating-flow-through (RFT-NSS) chamber. Performance and observational data are presented for different chamber vent designs, sealing mechanisms between the chamber pan and lid, recirculation pumps, and presence/absence of an internal fan that mixes headspace air within the sealed chamber. As examples of the repeatability and precision of the methodology, ten consecutive flux measurements were obtained using moist manure (32.6% wet basis water content, WCWB) within a 15 min period in which chamber pans were fitted with lids for 60 s and removed for 30 s. The mean calculated N2O flux was 43.08 +/- 0.89 mg N2O m(-2) h(-1). Using dry manure (WCWB = 10.8%), five consecutive flux measurements showed a very low, but consistent, flux that averaged 0.025 +/- 0.0016 mg N2O m(-2) h(-1). Five case study experiments demonstrate the usefulness of these chamber systems and highlight discoveries and lessons learned to enhance future research efforts. Major discoveries and observations include: (1) installation of a small internal fan within the chamber lids decreased N2O fluctuation over small time periods, allowing precise measurement of manure N2O fluxes as low as 0.0073 mg N2O m(-2) h(-1) during a 60 s measurement period; (2) two distinct N2O peaks were observed at 1 and 21 d following the addition of water to manure (initial WCWB = 32.6%), with the second peak accounting for 83% of the total N2O emitted over 45 d; and (3) there was notable diurnal variation in N2O fluxes due to temperature variation, even when the manure was dry (WCWB = 10.8%). These flux chamber systems proved to be more rapid, precise, and repeatable than traditional flux chamber methods and offer promise for future greenhouse gas emissions research on manure and soil.

Cattle grazing wheat pasture in the southern Great Plains are sometimes fed an energy supplement; however, the benefits of supplementation on nutrient balance, energy metabolism, and greenhouse gas emissions have not been elucidated. Therefore, we used 10 British crossbred steers (206 ± 10.7 kg initial BW) in a respiration calorimetry study to evaluate the effects of energy supplementation on energy losses, N balance, and nutrient digestibility of steers fed green-chopped wheat forage. The study design was an incomplete replicated 4 × 4 Latin square with treatments in a 2 × 2 factorial arrangement. Steers ( = 8) were assigned to 1 of 2 BW blocks (4 steers per block) with dietary factors consisting of 1) no supplementation (CON) or supplemented with a steam-flaked corn-based energy supplement (that also contained monensin sodium) at 0.5% of BW daily (SUP) and 2) NEm intakes of 1 times (1x) or 1.5 times (1.5x) maintenance. Wheat forage was harvested daily and continuously fed as green-chop to steers during the 56-d study. There were no differences ( ≥ 0.32) between CON and SUP for OM (78.3 vs. 80.7%, respectively) or NDF (68.3 vs. 64.8%, respectively) digestibility. At the 1.5x level of intake, there was no difference ( ≥ 0.16) in energy lost in feces (4.27 vs. 3.92 Mcal/d) or urine (0.58 vs. 0.55 Mcal/d), heat production (8.69 vs. 8.44 Mcal/d), or retained energy (3.10 vs. 3.46 Mcal/d) between supplementation treatments. Oxygen consumption (1,777 vs. 1,731 L/d; = 0.67) and CO production (1,704 vs. 1,627 L/d; = 0.56) of CON and SUP steers, respectively, were not different; however, SUP steers tended to have ( = 0.06) lower CH production (115 vs 130 L/d) than CON steers. Methane, as a proportion of GE intake, was similar for CON (6.87%) and SUP (6.07%; = 0.18), as was the ME:DE ratio ( = 0.24; 86.3% for CON and 87.9% for SUP). Fractional N excretion in urine and feces, as a proportion of total N excreted ( ≥ 0.84) or N intake ( ≥ 0.63), was not different between treatments. Calculated NEm and NEg values for CON were 1.76 and 1.37 Mcal/kg DM, respectively, whereas the NEm and NEg values for the SUP treatment were 2.32 and 1.61 Mcal/kg DM, respectively. Calculated NE values for steers fed additional energy were approximately 17.5% greater than the expected difference in energy content. This was probably the result of the inconsistent response at the 1x DMI level. Under these circumstances, energy supplementation did appear to enhance NEm and NEg value of the supplemented wheat forage diet.

An indirect calorimetry trial examined energy metabolism, apparent nutrient digestibility, C retention (CR), and N retention (NR) of cattle supplemented with zilpaterol hydrochloride (ZH). Beef steers ( = 20; 463 ± 14 kg) blocked ( = 5) by weight and source were individually fed and adapted to maintenance energy intake for 21 d before allotment to ZH (90 mg/steer∙d) or no β-adrenergic agonist treatment (control [CONT]) for 20 d (455 ± 14 kg at the start of treatment). Respiration chambers = 4 were used to quantify heat production (HP) during maintenance (d 12 to 16 of the ZH period) and fasting heat production (FHP; d 19 to 20 of ZH period; total 4 d of fast). Steers were harvested after a 6-d ZH withdrawal and carcasses were graded 24 h after harvest. Control cattle lost more BW ( < 0.01; 9 kg for CONT and 2 kg for ZH-treated) during maintenance whereas the BW loss of ZH-treated steers was greater ( < 0.01; 9 kg for ZH-treated and vs. 4 kg, for CONT) during FHP; no differences ( ≥ 0.76) were detected for G:F, ADG, and end BW. No differences in DMI, apparent nutrient digestibility, O consumption, or CH production ( ≥ 0.12) were detected; however, ZH-treated cattle had greater CO production during maintenance ( = 0.04; 23.6 L/kgBW for ZH-treated and 22.4 L/kg BW for CONT). Digestible energy and ME did not differ ( ≥ 0.19); however, urinary energy was greater ( = 0.05; 0.091 Mcal for CONT and 0.074 Mcal for ZH-treated) in CONT cattle. Steers treated with ZH tended to have greater HP ( = 0.09; 12.44 Mcal for ZH-treated and 11.69 Mcal for CONT), but the effect was reduced on a BW basis ( = 0.12; 0.126 Mcal/kg BW0.75 for ZH-treated and 0.120 Mcal/kg BW0.75 for CONT vs. 0.120 Mcal/kg BW). No treatment difference in FHP was observed ( ≥ 0.32) although CO production (L/steer) increased with ZH treatment ( = 0.04; 1,423 L/steer for ZH-treated and 1,338 L/steer for CONT). Control cattle excreted more ( = 0.05) N in urine (39.8 g/d for CONT and 32.4 g/d for ZH-treated); therefore, NR ( = 0.07; 22.14 g/d for ZH-treated and 14.12 g/d for CONT steers) tended to be greater for ZH-fed steers. Steers treated with ZH lost more C via CO ( = 0.04; 1,036.9 g/d for ZH-treated and 974.3 g/d for CONT) although total CR did not differ ( ≥ 0.23). Empty BW, HCW, and harvest yields (g/kg empty BW) were not different ( ≥ 0.13), whereas ZH increased dressed yield ( = 0.02; 62.12 % for ZH-treated and 60.65% for CONT) and LM area ( = 0.02; 77.81 cm for ZH-treated and vs. 70.90 cm for CONT). Separable carcass lean and actual skeletal muscle protein (SMP) were increased with ZH ( ≤ 0.04; 201.6 and 41.2 kg, respectively for ZH-treated and 196.0 and 38.4 kg, respectively for CONT). Results from this trial indicate that ZH treatment increased ( = 0.03) SMP and tended ( ≥ 0.07) to increase NR and modify HP during maintenance by increasing CO production.

Data from 3 trials were compiled to calculate microbial CP (MCP) production and MP requirements of growing calves on high forage diets. Individually fed steers (n = 335; 256 ± 15.6 kg midpoint BW) were utilized, each trial lasted 84. Diets consisted of 44% sorghum silage, 44% corn cobs, and 12% protein supplement. Source of protein within the supplement varied and included urea, meat and bone meal, soybean meal, feather meal, poultry by-product meal, or corn gluten meal. All trials included a urea only treatment. Dry matter intake of all calves within a trial was held constant, as a percent of BW, established by the urea supplemented group. The base diet was MP deficient, composition of the protein supplement varied with increasing amounts of test protein replacing urea. As protein in the diet increased, ADG plateaued. This methodology was used by Wilkerson et al. (1993) and is the basis of performance models used by the NRC (1996). Gain ranged from 0.19 to 0.56 kg/d, averaging 0.37 kg/d. Three microbial efficiencies were used to calculate MP. Maximum gain was then regressed against calculated MP to determine MP requirement for maintenance and gain. Method 1 (based on a constant 13% microbial efficiency suggested by the NRC, 1996) predicted an MP requirement of 3.4 g/kg BW0.75 for maintenance and 461 g/kg gain (r2 = 0.55). Method 2 (based on an equation developed by Patterson et al., 2006) predicted MP requirements of 2.9 g/kg BW0.75 and 483 g/kg gain (r2 = 0.56). Method 3 (based on an equation developed by Galyean et al., 2014) predicted MP requirements of 2.6 g/kg BW0.75 and 449 g/kg gain (r2 = 0.59). The factorial method of calculating MP maintenance requirements accounts for scurf, endogenous urinary, and metabolic fecal protein losses and averaged 4.2 ± 0.10 g/ kg BW0.75, for the 3 trials summarized here. Factors affecting MCP production include TDN, RDP, and microbial efficiency. Dietary TDN and RDP have been measured on a variety of feedstuffs; microbial efficiency is not well defined and is a crucial component in calculating MCP production and MP requirements of growing cattle.

One experiment was conducted to evaluate the influence of glycerin (GLY) on animal performance and health when used as a partial replacement for roughage in receiving diets. The second experiment was conducted using ruminally and duodenally cannulated steers in a 4 × 4 Latin square to determine the site of nutrient digestion and ruminal fermentation characteristics when GLY replaced roughage at 0%, 2.5%, 5%, and 10% of diet DM. In Exp. 1, steers (initial BW = 245 ± 2.3 kg) were fed treatment diets over a 42-d period that consisted of a control diet based on steam-flaked corn with GLY inclusion in replacement of dietary roughage at 0%, 5%, and 10% of diet DM. A linear reduction in DMI was observed as GLY increased (P = 0.01). Glycerin incorporation tended to improve G:F in a linear manner (P = 0.07); efficiency was improved 5.4% and 4.7% at 5% and 10% GLY. The number of animals receiving treatment for bovine respiratory disease did not differ among treatments. Furthermore, there were no differences among treatments for mortality or the frequency of steers that were seropositive for serum antibody titers to infectious bovine rhinotracheitis on d 28. In Exp. 2, apparent OM and apparent and true starch digestibility increased linearly (P < 0.05) as GLY concentration increased, whereas true OM digestibility responded in a quadratic (P < 0.01) manner. Bacterial OM and bacterial starch flow responded quadratically (P ≤ 0.02), and flow increased from 0% to 5% GLY inclusion and decreased thereafter. Feed OM flow responded quadratically (P ≤ 0.05), where it decreased from 0% to 2.5% GLY and increased from 2.5% to 10% GLY inclusion. Feed starch (P = 0.02) and total starch (P = 0.02) flow from the duodenum decreased linearly as the concentration of GLY increased in the diet. Bacterial N flow to the duodenum responded quadratically (P < 0.01); it increased with increasing GLY in the diet up to 5% and then decreased from 5% to 10%. The acetate to propionate (A:P) ratio in the ruminal fluid decreased (P < 0.05) as the concentration of GLY in the diet increased, which could have implications on improved G:F. The decrease in the A:P ratio as GLY increased in the diet, coupled with the linear decrease in DMI and improvement in G:F with GLY addition up to 5% of DM in place of roughage, implies that GLY is a viable dietary ingredient in growing and receiving diets.

Ethanol producers remove lipid from distillers grains (DG) for applications such as biodiesel production. The effects of the lipid removal on ruminal protein degradability and total-tract CP digestibility of DG are not known. Five ruminally and duodenally cannulated Angus-cross steers (BW = 434 ± 15 kg) were used to incubate in situ bags for determination of protein digestibility of low-lipid (5.54%) DG, medium-lipid (8.40%) DG, high-lipid (12.46%) DG, and cottonseed meal. Ingredients were weighed into individual in situ bags and incubated in the ventral sac of the rumen for 16 h. After ruminal incubation and simulated abomasal digestion, bags were inserted into the duodenal cannula of corresponding steers and collected from feces approximately 12 to18 h later. Bags were washed, dried, and analyzed for CP. The CP concentration in DG increased with decreasing lipid concentrations, and the RUP fraction of the CP in DG decreased with decreasing lipid concentration (54.5, 54.8, and 60.1 ± 1.8% RUP for low-, medium-, and high-lipid DG, respectively) suggesting that lipid extraction increased rumen protein degradability. The total-tract indigestible protein and postruminal digestibility of RUP were not different among the varying lipid concentrations in DG. The RUP digestibility of the low-, medium-, and high-lipid DG (79.5, 80.4, and 80.6 ± 2.0%, respectively) was consistent with the commonly used NRC model value of 80%. These data suggest the extraction of lipid from DG may alter ruminal degradability of CP but does not change the postruminal digestibility of the RUP.

Two hundred sixty-four crossbred heifers (initial BW = 354 kg ± 0.5) were used to determine effects of corn processing method and wet distillers grains plus solubles (WDGS) inclusion in finishing diets on animal performance, carcass characteristics, and manure characteristics. The study was conducted as a randomized complete block with a 2 × 2 factorial arrangement of treatments. Dietary treatments included steam-flaked corn (SFC)- and dry-rolled corn (DRC)-based finishing diets containing 0 or 20% WDGS (0SFC, 20SFC, 0DRC, and 20DRC, respectively). Heifers averaged 154 d on feed and were marketed in 3 groups. There were no interactions between corn processing method and WDGS detected (P ≥ 0.29) for any performance or carcass response variables. Heifers fed diets containing WDGS tended to have greater final BW (P = 0.10) and increased G:F (P = 0.08) compared with heifers fed diets without WDGS. Heifers fed SFC-based diets consumed 7% less feed (P < 0.01) and were 9% more efficient (P < 0.01) than heifers fed DRC-based diets. Carcass characteristics were not affected by corn processing method or WDGS inclusion (P ≥ 0.16). Intakes of OM, N, P, and K were greater (P ≤ 0.05) for heifers fed DRC-based diets than those fed SFC-based diets, which resulted in greater net accumulation of the nutrients in the manure (P ≤ 0.04). Heifers fed diets containing WDGS had greater (P < 0.01) intakes of N, P, and K than heifers fed diets without WDGS. As a result, a greater net accumulation of P and K (P ≤ 0.03) and N (P = 0.10) were present in the manure from cattle fed diets containing WDGS compared with those fed diets without WDGS. There was no interaction (P ≥ 0.16) between corn processing and WDGS on N volatilization losses. Nitrogen volatilization losses from manure (expressed as a percentage of intake and g·heifer(-1)·d(-1)) were greater (P < 0.01) for heifers fed SFC-based diets than heifers fed DRC-based diets. Feeding DRC-based finishing diets to heifers resulted in increased manure production and nutrient excretion and decreased N volatilization. Both corn processing method and WDGS inclusion affected animal performance and manure characteristics.