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The Role of Ciliate Protozoa in the Rumen
Open accessAbstract
First described in 1843, Rumen protozoa with their striking appearance were assumed to be important for the welfare of their host. However, despite contributing up to 50% of the bio-mass in the rumen, the role of protozoa in rumen microbial ecosystem remains unclear. Phylogenetic analysis of 18S rDNA libraries generated from the rumen of cattle, sheep, and goats has revealed an unexpected diversity of ciliated protozoa although variation in gene copy number between species makes it difficult to obtain absolute quantification. Despite repeated attempts it has proven impossible to maintain rumen protozoa in axenic culture. Thus it has been difficult to establish conclusively a role of ciliate protozoa in rumen fiber degradation. The development of techniques to clone and express ciliate genes in λ phage, together with bioinformatic indices to confirm the ciliate origin of the genes has allowed the isolation and characterization of fibrolytic genes from rumen protozoa. Elimination of the ciliate protozoa increases microbial protein supply by up to 30% and reduces methane production by up to 11%. Our recent findings suggest that holotrich protozoa play a disproportionate role in supporting methanogenesis whilst the small Entodinium are responsible for much of the bacterial protein turnover. As yet no method to control protozoa in the rumen that is safe and practically applicable has been developed, however a range of plant extract capable of controlling if not completely eliminating rumen protozoa have been described.
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In the citing paper
“Rumen bacteria play a dominant role in fiber digestion, although anaerobic fungi and protozoa have been reported to contribute to lignocellulose breakdown by attacking lignocellulosic material differently (60, 64) and discharging different enzyme complexes (101).”
From Phytogenic Additives Can Modulate Rumen Microbiome to Mediate Fermentation Kinetics and Methanogenesis Through Exploiting Diet–Microbe Interaction (2020) · cites this paper as [64]
Experimental — accuracy not yet measuredIn the citing paper
“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 Newbold et al., 2015
In the citing paper
“Based on their analysis, Newbold and colleagues found evidence that the removal of protozoa from the rumen caused a decrease in organic matter degradation, especially of neutral and acid detergent fiber.”
From Addressing global ruminant agricultural challenges through understanding the rumen microbiome: past, present, and future (2018) · cites this paper as Newbold et al., 2015
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“The protozoa also vary greatly in ruminants in terms of abundance or diversity, but their presence or absence is not greatly impactful to the host as a great amount of their products can also be synthesized by other groups of the gut microbiota [9, 12].”
RetractedMorm, S., Lunpha, A., Pilajun, R., & Cherdthong, A. (2023) · Tropical Animal Science Journal · doi:10.5398/tasj.2023.46.1.105 · Cited by 5
The utilization and digestion of cellulose by the rumen ciliate Diploplastron affine
Czauderna, M., Wereszka, K., & Michałowski, T. (2019) · European Journal of Protistology · doi:10.1016/j.ejop.2019.01.003 · Cited by 5
Ramos‐Morales, E., Tibble-Howlings, J., Lyons, L., OGBU, M. O., Murphy, P. J., Bragança, R., & Newbold, C. J. (2019) · Scientific Reports · doi:10.1038/s41598-019-38977-x · Cited by 5
Uncovering complex molecular networks in host–pathogen interactions using systems biology
Peters, J. M., Solomon, S. L., Itoh, C. Y., & Bryson, B. D. (2019) · Emerging Topics in Life Sciences · doi:10.1042/etls20180174 · Cited by 5
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“It seems that feeding the CS diet favoured the colonisation and growth of fibre degraders, such as fungi, R. albus and R. flavefaciens , and possibly some protozoa (41) .”
Dietary Manipulation to Mitigate Greenhouse Gas Emission from Livestock
Khusro, A., Aarti, C., Elghandour, M. M. M. Y., Adegbeye, M. J., Mellado, M., Barbabosa‐Pliego, A., Rivas-Cáceres, R. R., & Salem, A. Z. M. (2022) · Springer eBooks · doi:10.1007/978-3-030-72579-2_131 · Cited by 5
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“According to Newbold et al. (2015), lower SCFA levels observed in defaunated ruminants appeared to emphasize the role of protozoa in SCFA synthesis and feedstuff degradation in the rumen.”
BackgroundBacterial species in the ruminal content of steers fed oilseeds in the diet
de Melo, H. S. A., Ítavo, L. C. V., de Castro, A. P., Ítavo, C. C. B. F., Caldas, R. D. A., Mateus, R. G., Niwa, M. V. G., de Moraes, G. J., Zornitta, C. D. S., Gurgel, A. L. C., et al. (2022) · Tropical Animal Health and Production · doi:10.1007/s11250-022-03399-x · Cited by 5
“The type of lipid can inhibit or not change rumen microbial species, resulting in direct toxicity against protozoa and Archaea, or may have toxic effects on cellulolytic bacteria (Machmüller et al., 2003; Zhou et al., 2015; Newbold et al., 2015).”
BackgroundCiliates from the faeces of the free-ranging dromedary from Oman: Morphology and molecular phylogeny
Kornilova, O. A., Ganyukova, A. I., Belokon, M. E., Platonov, V. V., & Chistyakova, L. (2023) · Protist · doi:10.1016/j.protis.2023.125993 · Cited by 5
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“Methanogenic activity in the rumen is a complex symbiotic process which involves substrates availability and the interactions of bacteria, protozoa, and archaea (Newbold et al. 2015).”
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The AusBeef model for beef production: II. sensitivity analysis
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“This is at odds with current literature, therefore future studies may investigate the effects of protozoa on rumen dynamics, perhaps by representing defaunation and its effects on VFA concentration (Newbold et al. 2015).”
ResultCremonesi, P., Severgnini, M., Battelli, M., Monistero, V., Penati, M., Gazzonis, A. L., Castiglioni, B., Rapetti, L., Manfredi, M. T., & Addis, M. F. (2025) · Frontiers in Microbiology · doi:10.3389/fmicb.2025.1595924 · Cited by 7
Kim, G., Lee, W., & Park, T. (2025) · Scientific Reports · doi:10.1038/s41598-025-10599-6 · Cited by 7
Belanche, A., Palma‐Hidalgo, J. M., & Yáñez-Ruíz, D. R. (2025) · Journal of Animal Physiology and Animal Nutrition · doi:10.1111/jpn.70024 · Cited by 5
“Thus, any associations between productive data and specific bacterial taxa represents an oversimplification of the microbial ecology, where other microbial groups (methanogens, protozoa and anaerobic fungi) can also play crucial roles (Newbold et al. 2015).”
The association of the rumen virome with methane emissions in dairy cattle
Marcos, C. N., Gutiérrez‐Rivas, M., Goiri, I., García-Rodríguez, A., & González-Recio, Ó. (2025) · Communications Biology · doi:10.1038/s42003-025-08896-x · Cited by 5
“Ruminal ciliates and fungi are often associated with methanogenic archaea, as they provide archaea with H 2 for methane production 37 – 39 .”
The Neglected Role of Heterotrophic Protists in Engineered Water Systems
Song, H., Dowdell, K., Delafont, V., Skerlos, S. J., & Raskin, L. M. (2025) · Environmental Science & Technology · doi:10.1021/acs.est.5c04958 · Cited by 4
Zhang, G., Li, J., Li, J., Liu, S., Lv, L., Liang, J., Tao, X., & Zou, W. (2026) · Biomass and Bioenergy · doi:10.1016/j.biombioe.2026.109320 · Cited by 5
Muslykhah, U., Phupaboon, S., Sommai, S., Suriyapha, C., & Wanapat, M. (2026) · Animal nutrition · doi:10.1016/j.aninu.2025.12.012 · Cited by 4
Yanza, Y. R., Setiawan, M. A., Fitri, A., Tanuwiria, U. H., Hidayat, C., Ramadhani, F., Hidayat, R., Fidriyanto, R., Harahap, R. P., Niderkorn, V., et al. (2026) · BMC Veterinary Research · doi:10.1186/s12917-026-05487-8 · Cited by 6
“Furthermore, protozoa are closely associated with methanogenic archaea and significantly contribute to hydrogen fermentation; thus, a reduction in protozoal abundance and activity can indirectly diminish the hydrogen supply available for methanogenesis [13, 62].”
Bharanidharan, R., Panyavong, X., Hong, W. H., Kim, T. H., Byun, J. S., Lee, Y., Tomple, B. M., Kim, K.-H., & Ibidhi, R. (2024) · Frontiers in Veterinary Science · doi:10.3389/fvets.2024.1467077 · Cited by 4
Rumen microbiota for cattle performance and greenhouse gas mitigation across the world
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The Role of Feed Additives in Enhancing Ruminant Performance and Sustainability
Serbester, U. (2025) · Veterinary medicine and science · doi:10.5772/intechopen.1010868 · Cited by 4
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Therapeutic Potential of Garlic (Allium sativum) in Ruminants
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“However, the activity of protozoa in breaking down amino acids is three times that of bacteria (Newbold et al. , 2015).”
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“Despite the fact that the protozoa constitute an important part of the rumen microbiota, their role in ruminal fermentation and digestion is still controversial (Williams and Coleman, 1992; Newbold et al. 2015).”
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Torres, R. D. N. S., Paschoaloto, J. R., Júnior, G. A. D. A., Ezequiel, J. M. B., Coelho, L. D. M., Neto, O. R. M., & Almeida, M. T. C. (2022) · Livestock Science · doi:10.1016/j.livsci.2022.104934 · Cited by 7
Coconut oil effects on in vitro ruminal fermentation and methanogenesis
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Metadata
- Authors
- Newbold, C. J., de la Fuente, G., Belanche, A., Ramos-Morales, E., & McEwan, N. R.
- Affiliations
- Aberystwyth University (GB)
- Corresponding author
- Newbold, Charles J.
- Venue
- Frontiers in Microbiology
- Publisher
- Frontiers Media SA
- Published
- 2015-11-26
- Volume
- 6
- Pages
- 1313-1313
- ISSN
- 1664-302X (ISSN-L)
- PMC
- PMC4659874
- OpenAlex
- W2177858583
- Cited by
- 637
- References
- 163
- Citations by year
- 2026: 70 · 2025: 67 · 2024: 71 · 2023: 84 · 2022: 81 · 2021: 65 · 2020: 63 · 2019: 46 · 2018: 45 · 2017: 36 · 2016: 8 · 2015: 1
- FWCI
- 5.26
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by
- Locations
- Frontiers in Microbiology (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- LA Referencia (Red Federada de Repositorios Institucionales de Publicaciones Científicas) (publishedVersion, cc-by)
- RECERCAT (Consorci de Serveis Universitaris de Catalunya) (publishedVersion, cc-by)
- UdL Open Repository (University of Lleida) (publishedVersion, cc-by)
- Open Access Institutional Repository at Robert Gordon University (Robert Gordon University) (publishedVersion, cc-by)
- LA Referencia (Red Federada de Repositorios Institucionales de Publicaciones Científicas) (submittedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Open Access Institutional Repository at Robert Gordon University (Robert Gordon University) (submittedVersion, cc-by)
- Funders
- Biotechnology and Biological Sciences Research Council (BB/J0013/1)
- Topics
- Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Ruminant Nutrition and Digestive Physiology
- Physical Sciences › Energy › Renewable Energy, Sustainability and the Environment › Anaerobic Digestion and Biogas Production
- Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Animal Nutrition and Physiology
- Keywords
- rumen ciliate protozoa, rumen microbiota, 18S rDNA phylogeny, Entodinium, methanogenesis, methane mitigation, microbial protein supply, plant extracts, cattle, sheep, goats
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