Enteric methane (CH) 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 CH emissions is beneficial for understanding the range of variability in individual animal emission production (g CH head [hd] d) and emission intensity (g CH kg average daily gain [ADG]). Here, we used field-based technology to determine enteric CH 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 CH emissions ranging from 113.3 to 261.7 g hd d across the sampling period. Daily CH production values were 20% higher for steers ( = 9) from a local ranch compared with steers ( = 3) that originated from a mixed-grass prairie in south-central Nebraska (202.63 vs. 169.03 g CH hd d). ADG of local steers was three times greater than their counterparts (0.54 vs. 0.18 kg hd d), resulting in lower emission intensity (g CH/ADG; emission intensity) from local steers compared with the naïve steers (237.6 vs. 418.5 emission intensity). In addition, we compared measured CH 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.

中文翻译：

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放牧大面积半干旱牧场的牲畜肠道甲烷排放概况

在广阔的半干旱牧场放牧的牛的肠内甲烷（CH）排放在很大程度上是未知的，这代表了肉牛行业的巨大知识差距。了解基线肠道 CH 排放量有助于了解个体动物排放量（g CH 头 [hd] d）和排放强度（g CH kg 平均日增重 [ADG]）的变异范围。在这里，我们使用基于现场的技术来确定 2022 年仲夏在科罗拉多州东北部的北美短草草原放牧的一岁公牛的肠道 CH 排放量。26 只动物在 30 天内（6 月 1-30 日）适应了采样设备。测量排放量之前（7 月 1-31 日）。十二头 (46%) 一岁公牛完全适应环境，在整个采样期间平均 CH 排放量在 113.3 至 261.7 g hd·d 之间。与来自内布拉斯加州中南部混合草草原的阉牛 (= 3) 相比，来自当地牧场的阉牛 (= 9) 的每日 CH 生产值高出 20%（202.63 克 CH hd d 与 169.03 g CH hd d）。本地阉牛的平均日增重是同类阉牛的三倍（0.54 vs. 0.18 kg hd d），导致本地阉牛的排放强度（g CH/ADG；排放强度）低于幼稚阉牛（237.6 vs. 418.5 排放强度） ）。此外，我们将测量的 CH 排放量与使用政府间气候变化专门委员会二级方法计算的预测排放量进行了比较；实测排放量比本地阉牛的预测高出 31%，比非本地阉牛的排放量高出 18%。结果表明，需要进一步研究解决大面积牧场中放牧动物肠道 CH4 排放问题。此外，工作应针对牧场生态系统和动物起源之间的比较工作的具体情况，以便更准确地评估与温室气体减排战略相关的放牧肉牛的可持续性。