Anim Sci J. 2020;91:e13472. wileyonlinelibrary.com/journal/asj | 1 of 11 https://doi.org/10.1111/asj.13472 © 2020 Japanese Society of Animal Science 1 | INTRODUCTION Ruminant husbandry, a prominent source of anthropogenic meth- ane (CH 4 ), has a considerable impact on global warming (Moss et al., 2000; Shibata & Terada, 2010). Globally, the emission of enteric CH 4 from ruminant livestock accounts for up to 28% of anthropo- genic CH 4 emissions and an estimated 30%–40% of emissions from agricultural sources (Beauchemin et al., 2008; Moss et al., 2000). Global CH 4 emissions increased by almost 40% from 1970 to 2004 (IPCC, 2007), and they are estimated to increase by 60% on the basis of proportional CH 4 emissions from expected livestock pop- ulations in 2030 (FAO, 2003). In addition to its influence on climate change, the formation of enteric CH 4 also leads to a significant en- ergy loss (2%–12%) of dietary gross energy intake (GEI) in ruminants (Pen et al., 2006). Supplementation of diets with leguminous forage is thought to mitigate CH 4 emissions from ruminants and improve Received: 29 July 2020 | Accepted: 9 September 2020 DOI: 10.1111/asj.13472 ORIGINAL ARTICLE Effects of oat hay and leguminous forage mixture feeding on enteric methane emission, energy utilization, and feed conversion efficiency in male crossbred Simmental beef cattle Wuchen Du 1 | Fujiang Hou 2 | Atsushi Tsunekawa 3 | Nobuyuki Kobayashi 3 | Fei Peng 1 | Toshiyoshi Ichinohe 4 1 International Platform for Dryland Research and Education, Tottori University, Tottori, Japan 2 State Key Laboratory of Grassland Agro- ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, Gansu, China 3 Arid Land Research Center, Tottori University, Tottori, Japan 4 Faculty of Life and Environmental Science, Shimane University, Matsue, Japan Correspondence Fujiang Hou, State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, Gansu 730000, China. Email: cyhoufj@lzu.edu.cn Atsushi Tsunekawa, Arid Land Research Center, Tottori University, Tottori 680-0001, Japan. Email: tsunekawa@tottori-u.ac.jp Funding information Marginal Region Agriculture Project of Tottori University; the Program for Changjiang Scholars and Innovative Research Team in the University of China, Grant/Award Number: IRT_17R50; Strategic Priority Research Program of Chinese Academy of Sciences of China, Grant/Award Number: XDA20100102 Abstract Dietary manipulation has the potential to mitigate methane (CH 4 ) emission and to maintain or enhance livestock productivity. We conducted two experiments to in- vestigate the effects of replacing oat hay by leguminous forages (alfalfa hay [AH], 0, 8, 16, and 24%, experiment 1; common vetch hay [CVH], 0, 10, 20, and 30%, experi- ment 2) on energy metabolism of crossbred Simmental cattle. In experiment 1, total volatile fatty acid (VFA) concentrations increased quadratically with increasing AH proportions ( p = .006) with a forage-to-concentrate ratio of approximately 50:50, whereas the CH 4 energy to gross energy intake ratio (CH 4 -E:GEI) was significantly lower with 16% AH compared with 24% AH diet ( p < .05). In experiment 2, there were no differences in the total VFA concentrations among the four diet groups with a forage-to-concentrate ratio of around 60:40 ( p > .05); however, CH 4 -E:GEI was significantly lower in the 30% CVH diet compared with the 10% CVH diet ( p < .05). There was no significant difference in feed conversion efficiency among the four diet groups in each experiment. The results suggest that substituting 16 and 30% oat hay by AH and CVH provide optimal diets with forage-to-concentrate ratios of 50:50 and 60:40, respectively, which may reduce CH 4 emission without compromising the feed conversion efficiency of crossbred Simmental cattle. KEYWORDS alfalfa, CH 4 emission, common vetch, dryland, Simmental cattle