Advanced estimation and mitigation strategies: a cumulative approach to enteric methane abatement from ruminants

REVIEW J Anim Sci Technol 2019;61(3):122-137 https://doi.org/10.5187/jast.2019.61.3.122 Journal of Animal Science and Technology pISSN 1598-9429 eISSN 2055-0391 Advanced estimation and mitigation strategies: a cumulative approach to enteric methane abatement from ruminants Mahfuzul Islam and Sang-Suk Lee* Ruminant Nutrition and Anaerobe Laboratory, Department of Animal Science and Technology, Sunchon National University, Suncheon 57922, Korea Abstract Methane, one of the important greenhouse gas, has a higher global warming potential than that of carbon dioxide. Agriculture, especially livestock, is considered as the biggest sector in producing anthropogenic methane. Among livestock, ruminants are the highest emitters of enteric methane. Methanogenesis, a continuous process in the rumen, carried out by archaea either with a hydrogenotrophic pathway that converts hydrogen and carbon dioxide to methane or with methylotrophic pathway, which the substrate for methanogenesis is methyl groups. For accurate estimation of methane from ruminants, three methods have been successfully used in various experiments under different environmental conditions such as respiration chamber, sulfur hexafluoride tracer technique, and the automated head-chamber or GreenFeed system. Methane production and emission from ruminants are increasing day by day with an increase of ruminants which help to meet up the nutrient demands of the increasing human population throughout the world. Several mitigation strategies have been taken separately for methane abatement from ruminant productions such as animal intervention, diet selection, dietary feed additives, probiotics, defaunation, supplementation of fats, oils, organic acids, plant secondary metabolites, etc. However, sustainable mitigation strategies are not established yet. A cumulative approach of accurate enteric methane measurement and existing mitigation strategies with more focusing on the biological reduction of methane emission by direct-fed microbials could be the sustainable methane mitigation approaches. Keywords: Accurate methane estimation, Methane mitigating approach, Direct-fed microbials Background Methane (CH4), one of the three main greenhouse gases (GHG) besides of carbon dioxide (CO2) and nitrous oxide (N2O), have a global warming potential of 28-fold than that of carbon dioxide (CO2) [1]. Agricultural sector is considered to contribute the biggest methane emission, which calculated around 50.6% from anthropogenic methane [2]. Within agriculture, the livestock sector contributes approximately 18% of the global anthropogenic GHG emission [3]. Among livestock, ruminant contributes about 81% of GHG [4] due to massive methanogenesis by rumen microbes, which produce 90% of total CH4 production from ruminants [5]. Globally, CH4 emissions of dairy and beef cattle denote 30% and 35% of the livestock sectors’ emissions. However, buffalos and small ruminants are lower contributors, demonstrating 8.7% and 6.7% of sector emissions, respectively [6]. The CH4 production in Received: Mar 7, 2019 Revised: Apr 9, 2019 Accepted: May 13, 2019 * Corresponding author: Sang-Suk Lee, Ruminant Nutrition and Anaerobe Laboratory, Department of Animal Science and Technology, Sunchon National University, Suncheon 57922, Korea. Tel: +82-61-750-3237, E-mail: This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © 2019 Korean Society of Animal Science and Technology. 122 https://www.ejast.org Mahfuzul Islam, et al. ruminants represents a gross energy loss from 2% to 14% of gross energy consumption [7]. Therefore, reduction of methane emission in animal conserves an energy and enhances productivity. For the fulfilling of nutrition demand of growing population, the number of domesticated animals increasing rapidly. This high number of animals is directly proportional to CH4 production. In developed countries, it often recommends culling of nonproductive and low-producing animals to reduce CH4 budget [8]. They maintained high-producing animals in herds for reducing CH4 emissions per unit of product. Conversely, this is often impractical for poor countries due to their socioeconomic and religious background. It is well established that with the increasing animal productivity, CH4 emissions also decrease per unit of products. There are many options for enhancing the productivity of animals such as the proper formulation of diets, supplementation of protein and energy to low-quality forages, ionophores, bovine somatotrophin, and probiotics [9]. Lately, both the increasing of animal production as well as decreasing the methane emission by the animal especially ruminants are the main focus among researchers throughout the world. A number of CH4 abetment strategies from ruminants have been revised earlier [2,8,10–26]. However, these strategies summarized more concreate and cumulative approaches to set up future research needs for sustainable methane mitigation strategies in ruminants focusing direct-feed microbials. As a part of cumulative approach, accurate estimation of methane production is also very important in order to make a suitable methane mitigation strategy. Therefore, this review also summarized the methods of enteric methane measurement and their applications. Rumen microbiome and methanogenesis The rumen microbiome including a wide variety of microorganisms, viz. bacteria, archaea, ciliated protozoa, fungi, and viruses, stay in a symbiotic relationship in a strict anaerobic condition within the rumen [27]. The protozoa can comprise up to 50% of the microbial biomass in rumen [28]. While, the fungi were estimated at around 8% of the total biomass [29] but may reach 20% in sheep [30]. The archaea include only 0.3%–4% [31], and the bacteria cover the remainder, characteristically the largest component of the rumen microbial biomass [26]. This rumen microbiome plays a significant role in feed fermentation within the rumen and produces different volatile fatty acids (VFAs), CO2 and H2. These VFAs are essential for energy metabolism and protein synthesis of the ruminant host [32]. Among the diverse rumen microbiomes, only a few of these have been successfully characterized earlier based on culture-techniques. Recently, the application of multi-omics techniques such as metagenomics by next-generation sequencing (NGS) or high-throughput sequencing [33–37], metatranscrip- https://doi.org/10.5187/jast.2019.61.3.122 tomics [38–40], metaproteomics [41,42], and metabolomics [43–45] have been increased greatly [40]. Methanogenesis is a process of CH4 production in the rumen where H2 reduced the CO2 with the help of methanogenic archaea [46]. CH4 production is the main way for H2 clearance from (...truncated)