Snapshot of Enteric Methane Emissions from Stocker Cattle Grazing Extensive Semiarid Rangelands

Abstract

Enteric methane (CH₄) emissions from cattle grazing extensive semiarid rangelands are largely unknown and represent a considerable knowledge gap for the beef cattle industry. Knowledge of baseline enteric CH₄ emissions is beneficial for understanding the range of variability in individual animal emission production (g CH₄ head [hd]⁻¹ d⁻¹) and emission intensity (g CH₄ kg⁻¹ average daily gain [ADG]⁻¹). Here, we used field-based technology to determine enteric CH₄ emissions from yearling steers grazing the North American shortgrass steppe in northeastern Colorado in midsummer 2022. Twenty-six animals were acclimated for 30 d (1−30 June) to the sampling equipment in the field before the measurement of emissions (1−31 July). Twelve (46%) yearling steers fully acclimated, with mean CH₄ emissions ranging from 113.3 to 261.7 g hd⁻¹ d⁻¹ across the sampling period. Daily CH₄ production values were 20% higher for steers (n = 9) from a local ranch compared with steers (n = 3) that originated from a mixed-grass prairie in south-central Nebraska (202.63 vs. 169.03 g CH₄ hd⁻¹ d⁻¹). ADG of local steers was three times greater than their counterparts (0.54 vs. 0.18 kg hd⁻¹ d⁻¹), resulting in lower emission intensity (g CH₄/ADG; emission intensity) from local steers compared with the naïve steers (237.6 vs. 418.5 emission intensity). In addition, we compared measured CH₄ emissions with predicted emissions calculated using the Intergovernmental Panel on Climate Change tier 2 methodology; measured emissions were 31% greater than predicted for the local steers and 18% greater than steers from nonlocal steers. Results indicate that further research addressing grazing animal enteric CH4 emissions in extensive rangelands is needed. Further, efforts should be context specific for comparative efforts across rangeland ecosystems and animal origin to inform more accurate assessments of sustainability of grazing beef cattle related to greenhouse gas mitigation strategies.