Greenhouse gas emissions from the beef industry are largely attributed to the grazing sector, specifically from beef cattle enteric methane emissions. Therefore, the study objective was to examine how forage diversity impacts forage productivity, nutritive value, animal performance, and enteric methane emissions. This study occurred over three consecutive grazing seasons (2018 to 2020) and compared two common Midwest grazing mixtures: 1) a simple, 50:50 alfalfa:orchardgrass mixture (SIMP) and 2) a botanically diverse, cool-season species mixture (COMP). Fifty-six steers and heifers were adapted to an Automated Head Chamber System (AHCS) each year (C-Lock Inc., Rapid City, SD) and stratified into treatment groups based on acclimation visitation. Each treatment consisted of four pastures, three 3.2-ha and one 1.6-ha, with eight and four animals each, respectively. Forage production was measured biweekly in pre- and postgrazed paddocks, and forage nutritive value was analyzed using near-infrared reflectance spectroscopy. Shrunk body weights were taken monthly to determine animal performance. Forage availability did not differ between treatments (P = 0.69) but tended lower in 2018 (P = 0.06; 2.40 t dry matter ha−1) than 2019 (2.92 t dry matter ha−1) and 2020 (P = 0.10; 2.81 t dry matter ha−1). Crude protein was significantly lower for COMP in 2018 compared with SIMP. Forage acid detergent fiber content was significantly lower for the COMP mixture (P = 0.02). The COMP treatment resulted higher dry matter digestibility (IVDMD48) in 2018 and 2019 compared with the SIMP treatment (P < 0.01). Animal performance did not differ between treatments (P > 0.50). There was a tendency for the COMP treatment to have lower enteric CH4 production on a g d−1 basis (P = 0.06), but no difference was observed on an emission intensity basis (g CH4 kg−1 gain; P = 0.56). These results would indicate that adoption of the complex forage mixture would not result in improved forage productivity, animal performance, or reduced emission intensity compared with the simple forage mixture.

中文翻译：

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牧草多样性对牧草生产力、营养价值、肉牛生产性能和肠道甲烷排放的影响

牛肉行业的温室气体排放主要归因于放牧部门，特别是肉牛肠道甲烷排放。因此，本研究的目的是研究牧草多样性如何影响牧草生产力、营养价值、动物生产性能和肠道甲烷排放。这项研究发生在三个连续的放牧季节（2018 年至 2020 年），并比较了两种常见的中西部放牧混合物：1）简单的 50:50 苜蓿：果园草混合物（SIMP）和 2）植物多样性的凉爽季节物种混合物（COMP ）。每年有 56 头公牛和小母牛适应自动头室系统 (AHCS)（C-Lock Inc.，拉皮德城，SD），并根据适应情况分为治疗组。每个处理包括四个牧场，三个 3.2 公顷和一个 1.6 公顷，每个有八只和四只动物，分别。每两周在放牧前和放牧后的围场测量草料产量，并使用近红外反射光谱分析草料营养价值。每月测量缩小的体重以确定动物的表现。不同处理之间的草料可用性没有差异（P = 0.69），但 2018 年（P = 0.06；2.40 吨干物质 ha-1）趋于低于 2019 年（2.92 吨干物质 ha-1）和 2020 年（P = 0.10；2.81 吨）干物质 ha-1)。与 SIMP 相比，2018 年 COMP 的粗蛋白显着降低。COMP 混合物的牧草酸性洗涤剂纤维含量显着降低（P = 0.02）。与 SIMP 处理相比，COMP 处理在 2018 年和 2019 年产生了更高的干物质消化率（IVDMD48）（P < 0.01）。动物表现在处理之间没有差异（P > 0.50）。在 agd-1 基础上，COMP 处理具有较低的肠道 CH4 产量的趋势（P = 0.06），但在排放强度基础上没有观察到差异（g CH4 kg-1 增益；P = 0.56）。这些结果表明，与简单的草料混合物相比，采用复合草料混合物不会提高草料生产力、动物性能或降低排放强度。