Using nutritional strategies to mitigate ruminal methane emissions from ruminants

Within the agricultural sector, animal production contributes to 14.5% of global anthropogenic greenhouse gas emissions and produces around 37% of global CH4 emissions, mainly due to ruminal fermentation in ruminants. Over 90% of CH4 is synthesized by methanogens in the rumen during carbohydrate fermentation. According to different substrates, methanogenesis pathways can be divided into four categories: (1) hydrogenotrophic pathway; (2) acetoclastic pathway; (3) methyl dismutation pathway; and (4) methyl -reducing pathway. Based on the principle of biochemical reactions in the methanogenesis pathways, this paper reviews the latest publications on CH4 decreases in ruminants and described three nutritional strategies in terms of dietary nutrient manipulation (feeding management, feed composition, forage quality and lipids), microbial manipulation (ionophore, defaunation, methanogen inhibitors and probiotics), and chemical manipulation (nitrate, organic acids, plant secondary metabolites and phlorotannins, or halides in seaweeds). For each mitigation strategy, the review discusses effectiveness for decreasing CH4 emissions, application prescription, and feed safety based on results from in vitro and in vivo studies. This review summarizes different nutritional strategies to mitigate CH4 emissions and proposed comprehensive approaches for future feeding interventions and applications in the livestock industry.