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Understanding beef cattle enteric emissions on extensive western U.S. rangeland systems is critical for implementing sustainable grazing practices that reduce greenhouse gas (GHG) emissions. These practices must also improve livestock and plant productivity and climate resiliency while maintaining or reducing production costs. However, enteric emissions of grazing cattle under different stocking rates and grazing management strategies are largely unknown for western U.S. rangelands. Thus, our objective was to evaluate the differences in enteric emissions of stocker steers grazing native rangeland. Yearling Angus steers (n = 127) were stratified by initial body weight (BW) to six groups, then randomly assigned to one of six pastures grazed from June to September 2023 at the South Dakota State University Cottonwood Field Station (Cottonwood, SD) as part of a long-term stocking rate trial (80+ yr). Each pasture was equipped with a GreenFeed (C-Lock Inc, Rapid City, SD) pasture system to measure individual animal CH4 and CO2 emissions for continuous grazing (CG) and rotational grazing (RG) strategies in three stocking rates (Light, Moderate, and Heavy, 0.32, 0.40, and 0.72 animal unit months, respectively) in a 2 x 3 factorial design. Differences in enteric emissions among stocking rate and grazing strategy were analyzed using a linear mixed effects model in R, using the lme4 package, with animal as a random effect, and a post-hoc contrast among treatments was assessed using the lsmeans package. Steer initial and final BW were similar (P > 0.05) among treatments. For CH4 emissions, there was a significant interaction between stocking rate and grazing strategy (P < 0.05). Specifically, CH4 emissions for moderate-RG (195 ± 4.3 g/d) were less than those from heavy-CG (221 ± 4.5 g/d) and light-RG (221 ± 4.7 g/d) over the study period (P < 0.05). For CO2 emissions, light-CG steers respired greater CO2 emissions (6892 ± 101 g/d) than heavy-RG (6398 ± 107 g/d; P < 0.05). All other treatment lsmeans were similar (P > 0.05) and intermediate to these treatment effects. The assessment of GHG emission values for cattle grazing native rangeland is essential for informing climate mitigation strategies, improving animal efficiency, and understanding changes in GHG emissions over production phases and across animal classes. [ABSTRACT FROM AUTHOR]

Our objective was to evaluate how virtual fencing grazing management during the stocker phase influences steer growth performance, carcass traits, and enteric emissions during the finishing phase. Angus steers [n = 96; initial body weight (BW) = 375 ± 7.2 kg) grazed native rangeland from 07 June 2023 to 31 August 2023 in Cottonwood, SD at South Dakota State University’s Cottonwood Field Station. Following summer grazing, steers were transported to Brookings, SD and fed for 130-d at the South Dakota State University Cow-Calf Education and Research Facility. During the summer grazing season, steers were assigned to different stocking rates (Light, Moderate, and Heavy, at 0.32, 0.42, and 0.72 animal unit months, respectively), and grazing strategies [continuous (CG) or virtual fencing rotational (RG)] in a 2 × 3 factorial design. Steers were transitioned from a 30% roughage to a 10% roughage diet over 21-d. The finishing diet (13.7% CP, 17.2% NDF, 1.36 Mcal/kg NEg, and 30 g/907-kg monensin sodium) was manufactured twice daily and provided ad libitum. Feed consumption was tracked using precision monitoring equipment (Insentec, The Hague, Netherlands). Steers were individually weighed on d 1 (entry BW), 21, 63, 90, and 130 and administered a steroidal implant (200 mg trenbolone acetate and 20 mg estradiol; Revalor-200, Merck Animal Health, DeSoto, KS) on d 21. Enteric emissions, including methane and carbon dioxide, were monitored using the GreenFeed trailer system (C-Lock Inc., Rapid City, SD), growth performance, carcass traits, and categorical carcass traits were analyzed in a factorial design using a randomized complete block design with individual steer considered the experimental unit. Final BW was determined from hot carcass weight divided by 0.625. Steers from heavy-CG had greater feedlot entry BW (P ≤ 0.05) compared with all treatments except light-CG and light-RG. Light-CG and light-RG had greater entry BW compared with heavy-RG (P ≤ 0.05). Gain efficiency was greater for light-CG compared with light-RG, moderate-CG, and heavy-CG (P ≤ 0.05), while moderate-RG and heavy-RG were intermediate (P ≤ 0.05). Steers from moderate-RG had greater marbling scores compared with heavy-RG (P = 0.05), and all other treatments were intermediate. Neither stocking density (P ≥ 0.15) nor grazing management strategy (P ≥ 0.13) had any influence on other measures of growth performance, emissions (CH4 and CO2 ) production rate, or carcass traits. These findings suggest that stocking density and grazing-management strategy (CG vs. virtual fencing-RG) influence gains on pasture and alter feedlot entry BW, highlighting the need for further investigation into their implications for greenhouse gas emissions, as well as for determining optimal stocking densities and management strategies for ranchers [ABSTRACT FROM AUTHOR]