Microbiology Research 2015; volume 6:6120 Use of feed additives for tures have risen considerably and the IPCC predicts increases in global average surface Correspondence: Roonal Pritam Kataria, Jai Hind reducing greenhouse gas temperature tobe 1.8-4°C by 2100.2 The aver- College, A Road, backbay Reclamation, emissions from dairy farms age arctic temperature in 2012 was about Churchgate. Mumbai 400020, India. 14.6°C, which is 0.6°C warmer than the mid- Tel.: +91 9664219103 Roonal Pritam Kataria 20th century baseline. The average global tem- E-mail: [email protected] perature has risen about 0.8°C since 1880, Jai Hind College, Mumbai, India Key words: CH4; methanogens; ruminants; ener- according to the new analysis.3 These temper- gy loss; greenhouse gas; reduction approaches. ature rises are much greater than those seen during the last century, when average temper- Conflcit of interest: the author declares no con- Abstract ature rose only 0.06°C per decade. Since the flict of interest. mid-1970s, however, the rate of increase in temperature rise has tripled.4 The IPPC’s Received for publication: 23 July 2015. This review analyses methane emissions report warns that climate change could lead to Revision received: 11 October 2015. from dairy farms due to enteric fermentations impacts on have tremendous impact on envi- Accepted for publication: 22 October 2015. and use of different feed additives as a strategy ronment, animals and humans that are abrupt This work is licensed under a Creative Commons to control them. CH4 is a product that forms or irreversible. during the fermentation of food in the rumen Attribution NonCommercial 3.0 License (CC BY- of ruminants and on average represents a 7% NC 3.0). loss of the energy ingested by the animal. CH 4 ©Copyright R.P. Kataria, 2015 is also a potent greenhouse gas. Various Contribution of ruminants to Licensee PAGEPress, Italy approaches have been studied in many coun- greenhouse gas Microbiology Research 2015; 6:6120 tries with the aim of reducing methane emis- doi:10.4081/mr.2015.6120 sions of digestive origin like the use of biotechnologies to modify the microbial The rising concentration of methane is ecosystem. This include selection of rumen correlated to increasing populations and cur- micro-organisms through the elimination of rently about 70% of methane production arises protozoans or the inoculation of exogenous from anthropogenic sources and the remain- Ruminal fermentation and the bacterial strains, vaccination against der from natural sources. Agriculture is con- production of methane methanogenic micro-organisms, etc. or use of sidered to be responsible for about two-thirds new food additives like plant extracts, organic of the anthropogenic sources.5 Biological gen- acids, etc. and are theoretically promising eration in anaerobic environments (natural Methane is produced as a result of anaer- paths. Their application is however still not and man-made wetlands, enteric fermentation obic fermentation in the rumen and the hind- known because trials are being performed and anaerobic waste processing) is the major gut. Enzymes present in the rumen hydrolyze mainly in vitro. This article focuses on reduc- source of methane. the dietary organic matter to aminoacids and ing methanogenesis by adjusting the composi- Agricultural sources derived from enteric simple sugars. The rumen is an ideal habitat tion of the feed distributed to animals. fermentation (81-92 million tonnes), paddy for a large and diverse microbial population.11 rice production (60-100 million tonnes), bio- The main functions of this group is to degrade mass burning (40 million tonnes) and animal plant polymers which cannot be digested by wastes (25 million tonnes) are the major the host enzymes. The feed material is fer- Introduction sources responsible for methane production.6 mented to volatile fatty acids (VFA), carbon At a global scale, livestock farming contributes dioxide and methane. These VFAs pass Methane is a potent greenhouse gas to 30-50% of total greenhouse gas emissions. through the rumen wall into the circulatory which absorbs the sun’s heat and warms the India has a livestock wealth of 272.1 million system and are oxidised in the liver, supplying atmosphere. Thus, if the concentration of heat cattles, 159.8 million buffaloes, 71.6 million a major part of the energy needs of the host. absorbing gas like methane increases, the sheep, 140.6 millions goats and 13.1 million Volatile fatty acids may also be directly utilised atmosphere will warm up resulting in global other ruminants which produce large amount by the host as building blocks for synthesis of warming. of methane as a part of their normal digestive cell material. Fermentation is also coupled to The global warming potential (GWP) of process.7 this constitutes about 20% of the microbial growth and the microbial cell protein 8 synthesised forms the major source of protein methane is 25 times higher than that of CO2, world’s ruminants population. Thus, in order and hence methane significantly contributes to improve the greenhouse gas balance of for the animal. The gases produced are waste to enhanced greenhouse effect. According to farming, methane reduction by ruminants is of products of the fermentation and are mainly NOAA reports in 2011, methane levels rose in great concern. It would have a rapid effect on removed from the rumen by eructation.12 A 2010 for the fourth consecutive year after the environment as the life span of methane in small proportion of methane is absorbed in the remaining nearly constant for the preceding 10 atmosphere is 12 years as compared to 100-200 blood and is eliminated through the lungs. 9 years, up to 1799 parts per billion. Methane years of CO2 and N2O, respectively. Decreasing Both methanogenic bacteria and protozoa concentration was measured 1794 ppb in 2009, methane emissions from these sources by 10 are involved in methane production in rumen. and 1714 ppb in 1990.1 One of the environmen- to 15% would stabilise atmospheric methane at Virtually all of the bacteria attached to proto- tal threats our planet faces today is the poten- its present level and is a realistic objective. zoa are methanogens. These bacteria are tial for long-term changes in the earth’s cli- Hence, enormous efforts are being made responsible for between 0.25 and 0.37% of the mate and temperature patterns known as glob- across the world to find methods that are effec- total methane produced. Besides protozoa, a al climate change. Average global tempera- tive, safe and sustainable.10 number of other organisms are also involved [Microbiology Research 2015; 6:6120] [page 19] Review in ruminal fermentation and methane produc- which rumen fermentation will be optimised terminals electron acceptor and therefore may tion.13 Rumen methanogenic archaebacteria requires an understanding of the nutrient behave as an alternate hydrogen sink, thereby utilize hydrogen and carbon dioxide or for- requirements of the mixed microbial popula- reducing the amount of methane produced mate, acetate, methylamine and methanol for tion. Growth of rumen microbes is influenced under anaerobic conditions. The nitrate and production of methane. The involvement of by chemical, physiological and nutritional nitrite along with CO2 are the hydrogen accep- these bacteria in inter-species hydrogen trans- components. The major chemical and physio- tors in the rumen. Conversion of nitrate to fer (maintaining low partial pressure of hydro- logical modifiers of rumen fermentation are nitrite and finally to ammonia is carried out by gen within the rumen) is an important inter- rumen pH and turnover rate and both of these rumen bacteria. action which alters the fermentation balance are affected by diet and other nutritionally Leng21 provided a comprehensive review and results in a shift of the overall fermenta- related characteristics such as level of intake, of the earlier literature on nitrates. Recent tion from less-reduced to more-reduced end- feeding strategies, forage length and quality research with sheep and cattle has shown products. and forage:concentrate ratios. Recent research promising results with nitrates decreasing CH4 has suggested that interventions in early life production by up to 50%. Asanuma et al.22 of the animal can trigger differential microbial investigated the effects of dietary nitrate addi- rumen colonization and development, which tion on ruminal fermentation characteristics Mitigation of methane emis- may result in differential rumen CH4 produc- and microbial populations in goats. As the sions tion. This interesting concept may offer new result of nitrate feeding, a decrease in the total opportunities for mitigating CH4 emission in concentration of ruminal volatile fatty acids Generally speaking, the level of methane ruminants but needs to be further tested and and the populations of methanogens, protozoa 16 production from the rumen is inversely related verified. Since methane represents a loss of and fungi was noted. Stoichiometric calcula- 23 to the quantity (energy value) and quality carbon from the rumen and therefore an tions by Hegarty show that to reduce (digestibility) of the feed an animal consumes. unproductive use of dietary energy, scientists methane emissions by 50%, about 0.75 moles As the amount of feed consumed increases, have been looking for ways to suppress its pro- of sulphate or nitrate ingestion per day is the energy available for conversion to methane duction. required. However, since sulphate and nitrate also increases. There is a relationship between are toxic to ruminants at approximately 0.1 methane emissions and feed digestibility. moles/day and 0.25 moles/day respectively, Therefore, if the effeciency with which the they cannot be fed safely at levels required to animal digests its feed is increased, the Forage selection and processing reduce methane emission. amount of energy released in the form of methane gas by rumen can be reduced.14 From Reduction in methane emissions have about 5-15% of the digestible energy in feed is been observed through forage selection.