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; ; 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 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 , 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 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 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. The lost as methane gas. So, if we could reduce the work of McCaughey et al.17 have shown that Organic acids amount of methane produced by cattle, we the difference in the carbohydrate fraction of could significantly reduce the amount of feed forages such as grass silage, maize silage, Within the rumen, methane represents a they need and also protect the environment legumes or whole crop wheat silage gives rise terminal hydrogen sink. Propionate production from the hazards of greenhouse effect. to difference in productivity. Hence, it is represents an alternative hydrogen sink in The most promising approach for reducing important to select forage species that result normal rumen fermentation, provided suffi- methane emissions from livestock is by in reduced methane production. Grinding and cient precursors are available.The main pre- improving the productivity and efficiency of pelleting of forages can markedly decrease cursors to propionate within this cycle are livestock production. Increasing animal pro- methane production. At high intakes methane pyruvate, oxaloacetate, malate, fumarate, and ductivity will generally reduce methane emis- loss/unit of diet can be reduced 20-40%. succinate, or alternatively directly from pyru- sions per kg of product (milk or meat). Similarly, the work carried out by van Gastelen vate to propionate via the acrylate pathway Because of the improvement in production et al.18 show that replacing Grass silage with (high concentrate diets). Any of these organic effeciency, a greater proportion of the energy Corn Silage in a common forage-based diet for acids may promote alternative metabolic path- in the animal feed is directed towards produc- dairy cattle offers an effective strategy to ways to dispose of reducing power and hence tion of useful products and hence methane decrease enteric CH4 production by 8% without reduce methane production. Existing research emissions per unit product is reduced. This negatively affecting dairy cow performance. shows this to be a very promising approach. will also lead to a reduction in herd size to pro- The study undertaken by Lettat et al.19 indicat- Workers in the UK and Spain have studied in 15 duce the given level of product. In the devel- ed a 13 and 6% reduction in CH4 per unit of vitro the effect of different concentrations of oped countries of the world, livestock milk out when feeding a 25:75 grass fumarate in the rumen fermentation.24 are kept in well managed production systems silage:corn silage diet compared with a 75:25 Callaway and Martin25 have considered the and generally fed diets that are very high in grass silage:corn silage diet. Independent effect of fumarate and malate on rumen fer- digestibility and nutrients. The result is very studies carried out by several group of workers mentation in vitro. Their results indicated that efficient production (milk or meat) relative to demonstrated that comparative high reduction malate addition not only acted as an alterna- the amount of methane emitted. in enteric methane emissions can be achieved tive hydrogen sink, like fumarate, but also Unfortunately, ruminants in developing coun- by increasing the forage quality combined with buffers the ruminal contents by a dual mecha- tries are kept on diets that are low in both the management of stocking rates and rota- nism of reducing lactate accumulation and digestibility and nutrient content. This leads tional strategies.20 increasing carbon dioxide production. It is not only to greatly increased methane emis- essential, particularly with high concentrate sions, but also very diminished productivity diets that the disposal of ruminal lactate is relative to the animals’ genetic potential. This efficient to avoid a severe decline in rumen inefficient productivity has global implica- Nitrates and sulphates pH. Martin26 found malate and fumarate, as tions. direct metabolic precursors of propionate, However, establishing conditions under Both nitrates and sulphates may serve as a reduce methane production when fed in a pure

[page 20] [Microbiology Research 2015; 6:6120] Review form or in high malate forages. It decreases of two types: hydrolysable and condensed tan- from ruminants. In a study, Quillaja saponin methane emissions by directing hydrogen into nins. The condensed tannins also called as and nitrate in combination at low dose inhibit- succinate rather than into methane. Asanuma proanthocyanidins, has a characteristic influ- ed methanogenesis substantially while et al.27 observed that the addition of fumarate ence on proteins and carbohydrates. Tannins increasing feed degradability.47 to rumen utilizers both hydrogen as well as for- have both bacteriocidal and bacteriostatic mate, which are the substrates for the effect and can also inactivate ruminal methane formation. Malate has similar effects enzymes. Tannins supress methanogenesis on fermentation as fumarate.28 directly through their antimethanogenic and Use of probiotics The option of the use of the organic acids defaunation property.37 as daily supplements to reduce methane would Tannins, as feed supplements or as tannif- Direct-fed microbials (DFM), in one form only be practicably available to livestock receiv- erous plants have a potential for reducing CH4 or another, are commonly used as supplements 38,39 40 ing supplementary concentrates in a controlled emission by up to 20%. Patra et al. has in animal production. The most widely used manner. If concentrations of these organic observed that there is A decrease in vitro microbial feed additives (live cells and growth acids in forages could be increased then the metane production with methanol extract of medium) are based on Saccharomyces cerevisi- option would be available to all ruminant live- harada (Terminalia chebula) at the level of ae (SC) and Aspergillus oryzae (AO). Their stock. 0.25/30 mL of incubation medium. He also effect on rumen fermentation and animal pro- observed a complete inhibition at double this ductivity are wide ranging and this has been level. Sources containing both hydrolysable reviewed by several authors.48,49 and condensed tannins were shown to be more Work carried out by Chaucheyras et al.50 Bacteriocins and ionophores potent than those containing only hydrolysable suggest that live yeast cells can stimulate the 41 42 tannins. According to Goel and Makkar, the use of hydrogen by acetogenic strains of rumi- Bacteriocins are naturally occuring bacte- antimethanogenic effect of tannins depends nal bacteria there by enhancing the formation on the dietary concentration and is positively rial products with a bacteriocidal activity. They of acetate and decreasing the formation of related to the number of hydroxyl groups in are effective as they directly inhibit methane. However, the effects of yeast are their structure. These authors concluded that methanogens and redirect H2 to other reduc- strain dependent.51 The other effects observed hydrolyzable tannins tend to act by directly tive rumen bacteria such as propionate-pro- include shift in fermentation towards butyrate ducer or acetogens. Callaway et al.29 have inhibiting rumen methanogens whereas the or propionate or reduction in protozoal num- shown that nisin – a food additive, reduces effect of condensed tannins on CH production 4 bers. These effects are variable and short- methanogenesis by 36%. However, the organ- is more through inhibition of fiber digestion. term, diminishing 2-4 hour after feeding. isms developed resistance quickly. This prob- Other DFM interventions of ruminal fermenta- lem can be overcome by the use of bacteriocin tion include inoculation with lactate-producing of rumen origin. They have a potential as new and lactate utilizing bacteria to promote more generation of rumen modifiers.30 Lee et al.31 Saponins desirable intestinal microflora and stabilize pH found that semipurified bacteriocin i.e. and promote rumen health, respectively.52 Bovicin HC5 inhibits 50% of methane produc- Saponins are complex compounds that are There have also been other attempts to inocu- tion in vitro and methanogens did not show composed of a saccharide attached to a steroid late the rumen with fungi (Candida kefyr) and any adaptation to these bacteriocins. or triterpene and have a soapy character due to lactic acid bacteria (Lactococcus lactis) along Ionophores are antibiotics produced by bacte- their surfactant properties. Several studies with nitrate supplementation to control ria. Ionophores increases the proportion of with saponins reported decreased CH produc- 4 methanogenesis, but no consistent animal gram positive bacteria in the rumen, resulting tion from about 6 to 27% by reducing the pro- data have been reported.53 in a shift in fermentation acids from acetate tozoa population.42 Saponins cause defauna- and butyrate to propionate, and hence decreas- tion through their binding with sterols present es the methane production.32 Monensin has on the protozoal surface. been the most studied ionophore and it is rou- Singal et al.43 found that 5 herbal products tinely used in beef production and more such as pulp powder of reetha (Sapindus Use of prebiotics recently in dairy cattle nutrition in many coun- mukorossi), shikakai (Acacia concinna), tries. There have been a number of experi- mahua (Madhuca indica) cake, albezia leaves The prebiotics or oligosaccharides are non ments with monensin as a rumen modifier in (Albizia lebbek) and yucca (Yucca schiagera) digestible carbohydrates normally used in the various production systems, where CH4 pro- reduces methane production in vitro. non ruminants for better gut health and feed duction was studied as a main objective either Inhibition of methane production upto 96% utilization. They are used in rumen manipula- from a mitigation or from an energy loss per- was reported with the ethanol and methanol tion along with nitrates, probiotics and yeast to spective.33-36 Although some studies reported a extracts of soap nut (Sapindus mukorossi).44 have reduced methane production. The long-term mitigating effect of monensin on Lila et al.45 studied the effect of different con- increase in cellulolytic rumen bacteria is pro-

CH4 production, overall the effect of the centrations of sarsaponin wherein 60% of vided by using prebiotic compounds such as ionophore on methane production appears to methane reduction was observed as the con- mannan-oligosaccharide (MOS), fructo- be inconsistent, transient and short-lived indi- centration increased from 1.2 to 3.2 g/L fer- oligosaccharide (FOS), galacto-oligosaccha- cating that microbial adaptation occurs. mentation medium. ride.54 Mwenya et al.55 showed that they Studies from China have reported enhances propionate production by stimulat-

decreased CH4 in ruminants treated with tea ing Selenomonas, Succinomonas and triterpenoid saponins but also substantial Megasphera with inhibition of acetate produc- Tannins changes in microbial populations, including a ers such as Ruminococcus and Butyrivibrio. reduction in protozoal counts.46 Combination The administration of galacto-oligosaccha- In plants, tannins exist as polyphenols of of saponin and nitrate may have practical rides have brought about reduction of methane varying molecular size and complexity and are application in mitigating methane emission prodution upto 11%.

[Microbiology Research 2015; 6:6120] [page 21] Review

coconut oil in the diet. Ruminal ciliate proto- expansion. The loss of membrane stability Vaccinations zoa rely on hydrogen producing fermentation results in the leakage of ions across the cell process that is inhibited by a high concentra- membrane, which causes a decrease in the The work of Baker56 have shown that it is tion of hydrogen. They share a symbiotic rela- transmembrane ionic gradient. In most cases, possible to immunize ruminants against their tionship with ruminal methanogens which bacteria can counterbalance these effects by own methanogens thereby reducing methane allows an interspecies hydrogen transfer, using ionic pumps and cell death does not emission. Methanogens are antigenically dis- thereby lowering the concentration of hydro- occur, but large amounts of energy are diverted tinct from other organisms in the rumen; gen for the ciliate protozoa. Therefore, less to this function and bacterial growth is slowed hence a vaccination can help in reduction of hydrogen is available for formation of methane down, resulting in changes in the fermenta- methane production by rumen methanogens. A after defaunation.64 tion profile.69 vaccine developed by Wright et al.57 containing Dong et al.65 compared canola oil to Several studies have documented reduc- 3 methanogen mixture produced a 7.7% reduc- coconut oil and demonstrated coconut oil as tion in methane production by EOs. tion in methane emission. However, at present more effective methane inhibitor. Kongmuna Supplementation of ruminant diets with EOs vaccines do not have sufficient efficacy for et al.66 reported that supplementation of can alter microbial populations, digestion and commercial use. coconut with garlic powder improved in vitro fermentation of diets, proteolysis, and Vaccines against rumen archaea are based ruminal fluid fermentation in terms of the VFA methanogenesis in the rumen.69-74 on the concept of a continuous supply of anti- profile, reduced methane losses and reduced In vitro studies demonstrated that garlic bodies to the rumen through saliva. Vaccines protozoal population. The inclusion of sun- oil reduced the emission of CH4. The active against archaea have been successful in flower oil to the diet of cattle resulted in 22% diallyldisulfide and allylmercaptan were vitro.58 decrease of methane emissions.67 The addition responsible for most of its effects. According to New approaches have involved identifica- of canola oil at 0%, 3.5% or 7% to the diets of Ankri and Mirelman74 its antimicrobial activity tion of genes encoding specific membrane- sheep reduced the number of rumen protozoa is due to the organo-sulphur compounds, par- located proteins from Methanobrevibacter by 88-97%.62 ticularly allicin. The anti-methanogenic effect ruminantium and using purified proteins (pro- However, fats and oils may pose numerous of garlic is due to direct inhibition of Archaea duced in Escherichia coli) as antigens to vacci- negative impacts to the animals. Dietary oil microorganisms in the rumen. Archaea have nate sheep.59 The development of vaccines, is supplementation caused lower fiber digestibil- unique membrane lipids that contain glycerol an exciting and fast-developing area of ity.67 Jordan et al.68 estimated that feeding linked to long-chain isoprenoid alcohols essen- research that may produce effective CH4 miti- copra meal containing coconut oil to animals tial for the stability of the cell membrane. The gation technologies in the future.60 takes a longer time to reach a common carcass synthesis of the isoprenoid units in weight and decrease the effects on total methanogenic Archaea is catalyzed by the methane emissions. Many factors need to be enzyme hydroxyl methyl glutaryl coenzyme A considered such as the type of oil, the form of (HMG-CoA) reductase. Gebhardt and Beck75 Fats and oils the oil (whole crushed oilseeds vs. pure oils), found that garlic oil is a strong inhibitor of and handling issues e.g. coconut oil has a melt- HMG-CoA reductase and hence the synthesis Oils offer a practical approach to reducing ing point of 25°C). High cost and the negative of the isoprenoid unit is inhibited, the mem- methane in situations where animals can be impact on milk fat concentration are some of brane becomes unstable, and the cells die. given daily feed supplements, but excess oil is the limitations of oil supplementation. Its Castillejos et al.76 reported the effects of detrimental to fiber digestion and animal pro- impact on milk fatty acid composition and Thyme (Thymus spp.) and oregano (Origanum duction. Both dietary oil and essential oil acts overall milk fat content would need to be care- spp.) oils on methane production. The active as modifiers of rumen fermentation. fully studied. Recent strategies, based on component thymol is a monoterpene with processed linseed, turned out to be very prom- strong antimicrobial activity against a wide Dietary oils ising in both respects.61 range of gram-positive and negative bacteria. Dietary oils like coconut oil, sunflower oil, Thymol affects the energy metabolism of 2 rel- mustard oil, horseradish oil have been found Essential oils evant rumen bacteria grown in pure culture: to reduce methane production in rumen. Essential oils (EO) are blends of second- Streptococcus bovis and Selenomonas rumi- Dietary fat seems a promising nutritional ary metabolites obtained from the plant nantium. It reduces methane concentrations alternative to depress ruminal methanogene- volatile fraction by steam distillation. They as well as total volatile fatty acid production sis without affecting other ruminal parame- have characteristic aroma or essence. They due to inhibition of microbial metabolism. It ters.61 Some of the possible mechanisms by have a very diverse composition, nature, and causes loss of integrity of the cell membrane which lipid supplementation reduces methane: activities. The most important active com- and a reduction in the uptake of glucose.77 The reducing fiber digestion (mainly in long chain pounds are included in 2 chemical groups: ter- effects of thymol are diet and pH dependent. fatty acids); suppression of methanogens and penoids (monoterpenoids and sesquiter- Therefore, it is important to define the condi- suppression of rumen protozoa62 and to a lim- penoids) and phenylpropanoids. These 2 tions under which these additives are used to ited extent through biohydrogenation of unsat- groups originate from different precursors of modify rumen microbial fermentation in the urated FA thereby serving as a hydrogen sink.63 the primary metabolism and are synthesized desired direction. 78 Machmulleur et al.62 observed coconut oil through separate metabolic pathways.69 Five essential oils (EOs), namely, clove oil as more effective inhibitor followed by rape- These compounds are as antiseptics and (CLO), eucalyptus oil (EUO), garlic oil (GAO), seed, sunflower seed, and linseed oil. Coconut antimicrobials. Due to the hydrophobic nature origanum oil (ORO), and peppermint oil oil comprises medium chain fatty acids. of the cyclic hydrocarbons; they interact with (PEO), were tested in vitro for their effect on Coconut oil control rumen methanogens by cell membranes and accumulate in the lipidic methane production. The CLO contains changing the metabolic activity and composi- bilayer of bacteria, occupying a space between eugenol (phenyl propanoid), EUO contains tion. A decrease in protozoa numbers has been the chains of fatty acids. This interaction caus- cineole (bicyclic monoterpinoid), GAO con- as identified as explanation for the reduction es conformational changes in the membrane tains alliin and allicin (organosulfur com- in methane emission after the inclusion of structure, resulting in its fluidification and pounds), ORO contains thymol (monoter-

[page 22] [Microbiology Research 2015; 6:6120] Review pinoid monocyclic phenol), and PEO contains ous possibilities associated with this and most tion and future challenges: an Indian per- menthol (monoterpinoid monocyclic non phe- of which require substantial amounts of spective. Livest Prod Climate Change nol). This study demonstrated that all the EOs research and development so as to apply multi- 2015;229. significantly reduced methane production with ple technologies to mitigate greenhouse gas 10. Grainger C, Beauchemin KA. Can enteric increasing doses. However, different EOs vary emission. However, strategies that can suc- methane emissions from ruminants be in their potencies in modulating rumen micro- ceed at farm level should be more practical and lowered without lowering their produc- bial populations and fermentation. Further, a involve no additional inputs. The potential of tion? Anim Feed Sci Technol 2011;166- single EO may not effectively and practically plant extracts in mitigating methane emission 167:308-20. mitigate methane emission from ruminants in ruminants is one such strategy that can be 11. Bryant MP. Normal flora-rumen bacteria. unless used at low doses in combinations with readily adopted as an on-farm practice. Since Am J Clin Nutr 1970;23:1440-50. other antimethanogenic compounds. 79 ruminants are so important to mankind as 12. Dougherty RW, Mullenaux CM, Allison MJ. they convert rich fibrous biomass of the world Physiology of digestion in the ruminant. into high quality protein sources i.e. meat and In: Dougherty RW, ed. London; milk for human consumption, more considera- Butterworth; 1965. p.159. Conclusions tions should be given to total farm greenhouse 13. Vogels GD, Hoppe WF, Stumm CK. gas emissions, and not just methane emis- Association of methanogenic bacteria with The experimental results obtained with sions from enteric fermentation when investi- rumen ciliates. Appl Environ Microbiol inhibition of methanogenesis in the rumen gating the issues. 1980;40:608-12. indicate that there exists a large number of 14. Hegarty RS. Strategies for mitigating chemicals, bacteriocins, antibiotics and plant methane emissions from livestock. secondary compounds like oils, tannins, Australian options and opportunities. saponins, etc which have the potential to mod- References Proceedings of 1st International ify the rumen microbial fermentation. Conference on Greenhouse Gases and However, each one of them is accompanied 1. NOAA. Greenhouse gas index continues Animal Agriculture. Obihiro, Japan; 2002. with one or the other drawback like simultane- climbing. 2011. 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