Reducing rumen methane emissions through elimination of rumen protozoa
Abstract
Methanogens living on and within rumen ciliate protozoa may be responsible for up to 37% of the rumen methane emissions. In the absence of protozoa, rumen methane emissions are reduced by an average of 13% but this varies with diet. Decreased methane emissions from the protozoa-free rumen may be a consequence of: ( 1 ) reduced ruminal dry matter digestion; ( 2 ) a decreased methanogen population; ( 3 ) an altered pattern of volatile fatty acid production and hydrogen availability; or ( 4 ) increased partial pressure of oxygen in the rumen. The decline in methanogenesis associated with removal of protozoa is greatest on high concentrate diets and this is in keeping with protozoa being relatively more important sources of hydrogen on starch diets, because many starch-fermenting bacteria do not produce H2. Because protozoa also decrease the supply of protein available to the host animal, their elimination offers benefits in both decreasing greenhouse gas emissions and potentially increasing livestock production. Strategies for eliminating protozoa are reviewed. None of the available techniques is considered practical for commercial application and this should be addressed.
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Defaunation reduces methane output by approximately 11%.
“protozoa have been linked to methanogenesis as defaunation reduces methane output by approximately 11% (Hegarty, 1999; Morgavi et al., 2010; Newbold et al., 2015).”
From Addressing global ruminant agricultural challenges through understanding the rumen microbiome: past, present, and future (2018) · cites this paper as Hegarty, 1999
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“Biohydrogenation of unsaturated FA can be an alternative sink for H2, but this is trivial compared with methanogenesis (Johnson and Johnson, 1995; Hegarty, 1999a).”
BackgroundMethane mitigation in ruminants: from microbe to the farm scale
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“measured in a chamber Hegarty et al. (2008)”
The role of ciliate protozoa in the rumen
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BackgroundInfluentialMethanogens: Methane Producers of the Rumen and Mitigation Strategies
Hook, S. E., Wright, A. G., & McBride, B. W. (2010) · Archaea · doi:10.1155/2010/945785 · Cited by 565 · see citing works
“Hegarty [73] found that defaunation reduced methane output 13%, but the magnitude of reduction varied with diet.”
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BackgroundPrediction of Methane Production from Dairy and Beef Cattle
Ellis, J. L., Kebreab, E., Odongo, N. E., McBride, B. W., Okine, E. K., & France, J. (2007) · Journal of Dairy Science · doi:10.3168/jds.2006-675 · Cited by 412 · see citing works
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Buddle, B. M., Denis, M., Attwood, G. T., Altermann, E., Janssen, P. H., Ronimus, R. S., Pinares-Patiño, C. S., Muetzel, S., & Wedlock, D. N. (2010) · The Veterinary Journal · doi:10.1016/j.tvjl.2010.02.019 · Cited by 187 · see citing works
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“No effect of saponin-rich fractions on methane production could also be documented to be diet dependent, where studies have shown slight effect of defaunation on methane production when animals were fed with roughages and no effect with a diet rich in starch (Hegarty 1999).”
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“Difference in diets may explain this variable effect as removal of protozoa has a more marked effect on methanogenesis with high concentrate diets (Hegarty, 1999).”
BackgroundStudy of methanogen communities associated with different rumen protozoal populations
Belanche, A., de la Fuente, G., & Newbold, C. J. (2014) · FEMS Microbiology Ecology · doi:10.1111/1574-6941.12423 · Cited by 147 · see citing works
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“In addition, ecto- and endosymbiotic relationships exist between protozoa and some methanogens, and their contribution is estimated at up to 37% of total methane production in the rumen (Dohme et al., 1999; Hegarty, 1999; McAllister and Newbold, 2008).”
BackgroundMeasurement and prediction of enteric methane emission
Sejian, V., Lal, R., Lakritz, J., & Ezeji, T. C. (2010) · International Journal of Biometeorology · doi:10.1007/s00484-010-0356-7 · Cited by 136 · see citing works
“Indeed, increasing the digestibility of pasture for grazing ruminants is the most practical means of reducing their CH4 emissions (Hegarty 1999).”
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Wanapat, M., Cherdthong, A., Phesatcha, K., & Kang, S. (2015) · Animal nutrition · doi:10.1016/j.aninu.2015.07.004 · Cited by 140 · see citing works
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“In addition, the increased proportion of propionate could be associated with a decrease in pH in the rumen, which has been suggested to slow down the activity of methanogens (10).”
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“Rumen ciliate protozoa are prodigious H2 producers, the main substrate for methanogenesis in the rumen, and their removal (defaunation; protozoa-free) yielded an average 13–45% lower CH4 emissions in vivo [107,155,160,161], but the results are not always consistent [141,150,162,163].”
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“, 1980), by removing the protozoal population through defaunation, the ruminal bacterial population is modified, VFA production is shifted from acetate and butyrate toward propionate, and CH4 production is reduced (Hegarty, 1999).”
BackgroundEffect of concentrate feed level on methane emissions from grazing dairy cows
Jiao, H., Dale, A. J., Carson, A. F., Murray, S., Gordon, A. W., & Ferris, C. P. (2014) · Journal of Dairy Science · doi:10.3168/jds.2014-7979 · Cited by 100 · see citing works
“In addition, the more rapid fermentation associated with concentrate-based diets tends to result in a lower rumen pH, and this will also inhibit the growth of methanogens and protozoa (Hegarty, 1999).”
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BackgroundClimate Change Impact, Adaptation, and Mitigation in Temperate Grazing Systems: A Review
Ghahramani, A., Howden, M. S., del Prado, A., Thomas, D., Moore, A. D., Ji, B., & Ateş, S. (2019) · Sustainability · doi:10.3390/su11247224 · Cited by 99 · see citing works
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BackgroundMethane mitigating options with forages fed to ruminants
Eugène, M., Klumpp, K., & Sauvant, D. (2021) · Grass and Forage Science · doi:10.1111/gfs.12540 · Cited by 95 · see citing works
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Szumacher-Strabel, M., & Cieślak, A. (2010) · Journal of Animal and Feed Sciences · doi:10.22358/jafs/66296/2010 · Cited by 90 · see citing works
“According to Hegarty (1999), methanogens associated with rumen protozoa are responsible for 9 to 25% of the total methane production during anaerobic fermentation in the rumen.”
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“Many studies have investigated the symbiotic microorganisms in the rumen because of their link to economically or environmentally important traits such as feed conversion efficiency [2,3], methane production [4,5], and more recently discovery of microbes and enzymes that enable fermentation of biomass for biofuel prod…”
BackgroundMitigation of ruminant methane production: current strategies, constraints and future options
Iqbal, M. F., Cheng, Y., Zhu, W., & Zeshan, B. (2008) · World Journal of Microbiology and Biotechnology · doi:10.1007/s11274-008-9819-y · Cited by 93 · see citing works
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“During feed fermentation, metabolic H2 is used for VFA production and also serves as an important substrate for reducing CO2 to CH4 by methanogens (Hegarty, 1999; Cottle et al., 2011).”
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The effects of livestock methane emission on the global warming: a review
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“The starch component of the diet is also known to promote propionate formation, through a shift to amylolytic bacteria and a reduction in ruminal pH, leading to a decrease in methanogenesis (van Kessel and Russell, 1996; Hegarty, 1999).”
BackgroundInfluentialProgress in the development of vaccines against rumen methanogens
Wedlock, D. N., Janssen, P. H., Leahy, S. C., Shu, D., & Buddle, B. M. (2013) · animal · doi:10.1017/s1751731113000682 · Cited by 79 · see citing works
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“, defaunation) has been shown to reduce methane emission by an average of 13% (14).”
BackgroundAlternatives for methane emission mitigation in livestock systems
Lascano, C. E., & Cárdenas, E. (2010) · Revista Brasileira de Zootecnia · doi:10.1590/s1516-35982010001300020 · Cited by 76 · see citing works
“The elimination of protozoa from the rumen has been shown to reduce the amount of enteric CH4 produced in a number of ways: a) lowered fiber digestion, b) reduced methanogen populations that are symbiotically associated with protozoa and c) reduced hydrogen production (Hegarty, 1999).”
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“…to name just a few (Van Nevel and Demeyer, 1995; Czerkawski et al., 1966; Mbanzamihigo et al., 1996; McCrabb et al., 1997; Mathison et al., 1998; Hegarty, 1999a, b; Joblin, 1999; Klieve and Hegarty, 1999; Machmüller and Kreuzer, 1999; Anderson et al., 2003; Machmüller et al., 2003a, b; Wright…”
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“Hegarty (1999) proposed that 37% of rumen methanogenesis originated from methanogens living in a methanogen-protozoan symbiotic relationship and Newbold et al. (1995) demonstrated that elimination of protozoa diminished methane production by 9 to 25% in vitro.”
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“Methane emissions and rumen protozoa It has been suggested that protozoa might increase methane production in the rumen through a combination of increased feed degradation and/or their symbiotic relation with methanogens (Hegarty 1999a; Morgavi et al., 2011).”
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“The H2 is generated during feed fermentation to produce VFA and also an essential substrate for CH4 formation by methanogens in the rumen (Hegarty, 1999; Cottle et al., 2011).”
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“Given that the introduction of grains into the ruminant diet generally decreases protozoal diversity (Hegarty, 1999) and also reduces CH4 production per unit of feed digested (Beauchemin et al.”
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Ma, T., Chen, D., Tu, Y., Zhang, N., Si, B., & Diao, Q. (2016) · Animal Science Journal · doi:10.1111/asj.12556 · Cited by 70 · see citing works
Nejad, J. G., Ju, M.-S., Jo, J., Oh, K., Lee, Y., Lee, S.-D., Kim, E.-J., Roh, S., & Lee, H.-G. (2024) · Animals · doi:10.3390/ani14030435 · Cited by 70 · see citing works
“These measurements are supplemented by bio-specimen analysis, which provides information on rumen microbial activity and methane generation mechanisms [80].”
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Khairunisa, B. H., Heryakusuma, C., Ike, K. A., Mukhopadhyay, B., & Susanti, D. (2023) · Frontiers in Microbiology · doi:10.3389/fmicb.2023.1296008 · Cited by 70 · see citing works
“These symbiotic methanogens representing 10–20% of rumen methanogens contribute to 15–35% of ruminal methane production (Hegarty, 1999; Morgavi et al., 2008, 2012).”
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“Hegarty (1999) postulated that, because of the close association between protozoa and methanogens, defaunation has decreased CH4 emissions by about 15%.”
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“However, these techniques seem not to be practical for its use in the ruminant production industry (Hegarty, 1999).”
Karnati, S. K. R., Sylvester, J. T., Ribeiro, C. V. D. M., Gilligan, L. E., & Firkins, J. L. (2009) · Journal of Dairy Science · doi:10.3168/jds.2008-1436 · Cited by 61 · see citing works
“In general, defaunation is expected to decrease methane production by approximately 15% (Hegarty, 1999) by removal of ecto- and endosymbionts.”
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“In addition, some studies have reported that CS reduced the number of methanogens by inhibiting the number of protozoa [47,48], which might explain the inhibition of methane production.”
BackgroundEffects of dietary sunflower seeds on rumen protozoa and growth of lambs
Ivan, M., Mir, P. S., Mir, Z., Entz, T., He, M. L., & McAllister, T. A. (2004) · British Journal Of Nutrition · doi:10.1079/bjn20041178 · Cited by 58 · see citing works
“There is at present no safe practical technique commercially available for the reduction or elimination of rumen fauna (Hegarty, 1999).”
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“Methane production was the same in the mixed fauna (532 lmol) and the fauna-free fermentors (531 lmol), although it is generally accepted that defaunation decreases methane emissions (Hegarty 1999; Boadi et al. 2004).”
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Opportunities for biological control of ruminal methanogenesis
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“Methanogenic archaea use the hydrogen to reduce carbon dioxide (CO2; Hegarty 1999; Moss et al., 2000).”
BackgroundPotential environmental benefits of feed additives and other strategies for ruminant production
Tedeschi, L. O., Callaway, T. R., MUIR, J. P., & Anderson, R. C. (2011) · Cited by 50 · see citing works
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Persistence of defaunation effects on digestion and methane production in ewes
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“Furthermore, Hegarty (1999) reviewed that methanogens living on and within rumen ciliate protozoa may be responsible for up to 37% of CH4 emissions, and these emissions are reduced by 13% on average in the absence of protozoa.”
BackgroundHegarty, R. S., Bird, S. H., Vanselow, B. A., & Woodgate, R. T. (2008) · British Journal Of Nutrition · doi:10.1017/s0007114508981435 · Cited by 46 · see citing works
“A review of the literature((3)) indicated that in the absence of protozoa, methane emissions were reduced by an average of 13%, with reductions in methane emissions of up to 25% being reported((28)).”
BackgroundSelf-citationEffect of dietary fat supplementation on methane emissions from dairy cows fed wheat or corn
Alvarez-Hess, P. S., Williams, S. R. O., Jacobs, J. L., Hannah, M. C., Beauchemin, K. A., Eckard, R., Wales, W. J., Morris, G. L., & Moate, P. J. (2019) · Journal of Dairy Science · doi:10.3168/jds.2018-14721 · Cited by 41 · see citing works
“It has been reported that methane production is associated with protozoa population, as methanogens residing on the exterior surface of the ruminal ciliate protozoa are estimated to produce up to 37% of the methane in the rumen (Hegarty, 1999; Brossard et al., 2004).”
BackgroundVillar, M. L., Hegarty, R. S., Nolan, J. V., Godwin, I. R., & McPhee, M. J. (2019) · Animal Feed Science and Technology · doi:10.1016/j.anifeedsci.2019.114294 · Cited by 41 · see citing works
“Some reviews have reported an increase in molar proportion of propionate after defaunation (Hegarty, 1999; Eugène et al., 2004) whereas Newbold et al.”
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“defaunation generally reduces ruminant methane emissions (7).”
Influence of genetically modified organisms on agro-ecosystem processes
Kolseth, A., D’Hertefeldt, T., Emmerich, M., Forabosco, F., Marklund, S. L., Cheeke, T. E., Hallin, S., & Weih, M. (2015) · Agriculture Ecosystems & Environment · doi:10.1016/j.agee.2015.08.021 · Cited by 36 · see citing works
Jiao, H., Yan, T., Wills, D., et al. (2013) · Agriculture Ecosystems & Environment · doi:10.1016/j.agee.2013.11.004 · Cited by 34 · see citing works
Efficacy of eucalyptus oil on in vitro ruminal fermentation and methane production
Sallam, S. M. A., Bueno, I. C. D. S., Brigide, P., Godoy, P. B. G., Vitti, D. M. S. S., & Abdalla, A. L. (2009) · Cited by 34 · see citing works
Ivan, M., Entz, T., Mir, P. S., et al. (2003) · Canadian Journal of Animal Science · doi:10.4141/a03-052 · Cited by 32 · see citing works
Moate, P. J., Deighton, M. H., Jacobs, J. L., Ribaux, B. E., Morris, G. L., Hannah, M. C., Mapleson, D., Islam, M. S., Wales, W. J., & Williams, S. R. O. (2019) · Journal of Dairy Science · doi:10.3168/jds.2019-17514 · Cited by 32 · see citing works
Henderson, G., Cook, G. M., & Ronimus, R. S. (2018) · Animal Production Science · doi:10.1071/an15757 · Cited by 31 · see citing works
“Redirection of hydrogen to enhanced propionate production via utility of ionophores, elimination of protozoa, or use of alternative electron receptors such as nitrate or sulfate, may indirectly lead to less methane being formed (Hegarty 1999; McAllister and Newbold 2008; van Zijderveld et al. 2010).”
BackgroundLagrange, S., MacAdam, J. W., & Villalba, J. J. (2021) · Agronomy · doi:10.3390/agronomy11112264 · Cited by 32 · see citing works
“Rumen defaunation, for instance, has been shown to reduce CH4 emissions from ruminants by 50%, due to the fact that protozoans are large producers of H2 with many methanogens among these microorganisms [13]; however, the lack of persistent response due to rapid adaptation and recovery of protozoal numbers along with i…”
BackgroundThe effect of oils fed to sheep on methane production and digestion of ryegrass pasture
Cosgrove, G. P., Waghorn, G. C., Anderson, C. B., et al. (2008) · Australian Journal of Experimental Agriculture · doi:10.1071/ea07279 · Cited by 31 · see citing works
Goopy, J. P. (2019) · Animal Production Science · doi:10.1071/an18457 · Cited by 31 · see citing works
“2012-6142 Alcock D, Hegarty RS (2006) Effects of pasture improvement on productivity, gross margin and methane emissions of a grazing sheep enterprise. International Congress Series 1293, 103–106. doi:10.1016/ j.ics.2006.01.080 Attwood GT, Altermann E, Kelly WJ, Leahy SC, Zhang L, Morrison M (2011) Exploring rumen met…”
InfluentialCarberry, C. A., Kenny, D. A., Kelly, A. K., & Waters, S. M. (2014) · Journal of Animal Science and Biotechnology/Journal of animal science and biotechnology · doi:10.1186/2049-1891-5-41 · Cited by 30 · see citing works
“It is widely accepted that both acetate and butyrate promote CH4 production, while propionate is considered a rival pathway to methanogenesis [42,43], directly competing with methanogens for available hydrogen during formation [5].”
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“Thus among the strategies to mitigate ruminal methane emission are: (1) Decreasing population and/or activity of methanogen, (2) Lowering the utilization of carbon dioxide and hydrogen by methanogen and (3) Defaunation of protozoa (Hegarty, 1999).”
MethodEffects of ruminal protozoa on methane emissions in ruminants—A meta-analysis
Dai, X., Kalscheur, K. F., Huhtanen, P. J., & Faciola, A. P. (2022) · Journal of Dairy Science · doi:10.3168/jds.2021-21139 · Cited by 29 · see citing works
Metagenome Analysis of Protein Domain Collocation within Cellulase Genes of Goat Rumen Microbes
Lim, S., Seo, J.-H., Choi, H., et al. (2013) · Asian-Australasian Journal of Animal Sciences · doi:10.5713/ajas.2013.13219 · Cited by 29 · see citing works
Hart, E. H., Christofides, S. R., Davies, T. E., Stevens, P. R., Creevey, C. J., Müller, C. T., Rogers, H. J., & Kingston‐Smith, A. H. (2022) · Scientific Reports · doi:10.1038/s41598-022-08309-7 · Cited by 28 · see citing works
Belanche, A., Kingston‐Smith, A. H., & Newbold, C. J. (2016) · Frontiers in Microbiology · doi:10.3389/fmicb.2016.00905 · Cited by 28 · see citing works
Qin, W.-Z., Li, C. Y., Kim, J. K., Ju, J.-M., & Song, M. K. (2012) · Asian-Australasian Journal of Animal Sciences · doi:10.5713/ajas.2012.12240 · Cited by 26 · see citing works
Linking rumen function to animal response by application of metagenomics techniques
Firkins, J. L., Karnati, S. K. R., & Yu, Z. (2008) · Australian Journal of Experimental Agriculture · doi:10.1071/ea08028 · Cited by 25 · see citing works
Ruminant Contributions to Methane and Global Warming — A New Zealand Perspective
Waghorn, G., & Woodward, S. (2005) · CRC Press eBooks · doi:10.1201/9780849330971.ch12 · Cited by 26 · see citing works
- Authors
- Hegarty, R. S.
- Corresponding author
- Hegarty, R. S.
- ORCID
- Hegarty, R. S.
- Venue
- Australian Journal of Agricultural Research
- Publisher
- CSIRO Publishing
- Published
- 1999-10-15
- Volume
- 50
- Issue
- 8
- Pages
- 1321-1328
- ISSN
- 0004-9409 (ISSN-L)
- 1444-9838
- OpenAlex
- W2505448068
- Cited by
- 213
- References
- 0
- Citations by year
- 2026: 8 · 2025: 6 · 2024: 3 · 2023: 4 · 2022: 10 · 2021: 8 · 2020: 8 · 2019: 14 · 2018: 9 · 2017: 7 · 2016: 15 · 2015: 14 · 2014: 19 · 2013: 11 · 2012: 14
- FWCI
- 3.20
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Australian Journal of Agricultural Research (publishedVersion)
- Topics
- Life Sciences › Agricultural and Biological Sciences › Agronomy and Crop Science › Ruminant Nutrition and Digestive Physiology
- Physical Sciences › Engineering › Building and Construction › Anaerobic Digestion and Biogas Production
- Physical Sciences › Environmental Science › Ecology › Agriculture Sustainability and Environmental Impact
- Keywords
- rumen protozoa, methanogenic archaea, methanogenesis, rumen ciliates, volatile fatty acids, hydrogen availability, high-concentrate diet, greenhouse gas emissions, animal husbandry
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