Abstract: Equine gut microbiology studies to date have primarily focused on horses and ponies, which represent only one of the eight extant equine species. This is despite asses and mules comprising almost half of the world's domesticated equines, and donkeys being superior to horses/ponies in their ability to degrade dietary fiber. Limited attention has also been given to commensal anaerobic fungi and archaea even though anaerobic fungi are potent fiber degrading organisms, the activity of which is enhanced by methanogenic archaea. Therefore, the objective of this study was to broaden the current knowledge of bacterial, anaerobic fungal and archaeal diversity of the equine fecal microbiota to multiple species of equines. Core taxa shared by all the equine fecal samples (n = 70) were determined and an overview given of the microbiota across different equine types (horse, donkey, horse × donkey and zebra). Results: Equine type was associated with differences in both fecal microbial concentrations and community composition. Donkey was generally most distinct from the other equine types, with horse and zebra not differing. Despite this, a common bacterial core of eight OTUs (out of 2070) and 16 genus level groupings (out of 231) was found in all the fecal samples. This bacterial core represented a much larger proportion of the equine fecal microbiota than previously reported, primarily due to the detection of predominant core taxa belonging to the phyla Kiritimatiellaeota (formerly Verrucomicrobia subdivision 5) and Spirochaetes. The majority of the core bacterial taxa lack cultured representation. Archaea and anaerobic fungi were present in all animals, however, no core taxon was detected for either despite several taxa being prevalent and predominant. Conclusions: Whilst differences were observed between equine types, a core fecal microbiota existed across all the equines. This core was composed primarily of a few predominant bacterial taxa, the majority of which are novel and lack cultured representation. The lack of microbial cultures representing the predominant taxa needs to be addressed, as their availability is essential to gain fundamental knowledge of the microbial functions that underpin the equine hindgut ecosystem.
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The research examines the diversity in the gut bacteria, fungi, and archaea present in different equine (horse family) species – including horses, donkeys, zebras, and horse-donkey hybrids. The study finds that despite some differences in microbial community composition, there exists a common core of microbes shared across all equine species.
Study Objectives and Approach
The primary aim of the study was to broaden our understanding of equine gut microbiota, focusing not just on horses and ponies, but across diverse (sub)species such as donkeys, zebras, and horse-donkey hybrids.
The study explored both bacterial and non-bacterial organisms, including anaerobic fungi and methanogenic archaea, both of which are important for the degradation of dietary fiber.
Scientists used fecal samples from these animals to determine the core taxa (major groups of species) shared by all equine types.
Key Findings
The fecal microbial concentrations and community compositions differed among the horse, donkey, zebra, and horse-donkey hybrids. Donkeys were found to have the most distinctive gut microbiota, while horses and zebras showed no notable differences.
Despite these variations, a common core of eight OTUs (operational taxonomic units – a way to classify groups of closely related individuals) and 16 genus-level groups was found in all the fecal samples.
This core constitutes a much larger proportion of the equine gut microbiota than was previously known. The core taxa are predominantly bacteria belonging to the Kiritimatiellaeota and Spirochaetes phyla.
Archaea and anaerobic fungi were found in all animals, but no core taxon was detected for them, despite their presence in many samples.
Implications and Conclusions
While the study observed differences between equine types, it identified a substantial core microbiota across all equines studied. This common core is mainly a few predominant bacterial taxa.
Most of these bacterial taxa have not been cultured in the lab, highlighting a gap in our understanding of their function. Resolving this gap would provide invaluable insights into the microbial functions that underpin the equine gut ecosystem.
Cite This Article
APA
Edwards JE, Shetty SA, van den Berg P, Burden F, van Doorn DA, Pellikaan WF, Dijkstra J, Smidt H.
(2020).
Multi-kingdom characterization of the core equine fecal microbiota based on multiple equine (sub)species.
Anim Microbiome, 2(1), 6.
https://doi.org/10.1186/s42523-020-0023-1
Shetty SA, Hugenholtz F, Lahti L, Smidt H, de Vos WM. Intestinal microbiome landscaping: insight in community assemblage and implications for microbial modulation strategies.. FEMS Microbiol Rev 2017 Mar 1;41(2):182-199.
Banerjee S, Schlaeppi K, van der Heijden MGA. Keystone taxa as drivers of microbiome structure and functioning.. Nat Rev Microbiol 2018 Sep;16(9):567-576.
Jónsson H, Schubert M, Seguin-Orlando A, Ginolhac A, Petersen L, Fumagalli M, Albrechtsen A, Petersen B, Korneliussen TS, Vilstrup JT, Lear T, Myka JL, Lundquist J, Miller DC, Alfarhan AH, Alquraishi SA, Al-Rasheid KA, Stagegaard J, Strauss G, Bertelsen MF, Sicheritz-Ponten T, Antczak DF, Bailey E, Nielsen R, Willerslev E, Orlando L. Speciation with gene flow in equids despite extensive chromosomal plasticity.. Proc Natl Acad Sci U S A 2014 Dec 30;111(52):18655-60.
FAOSTAT. 2016. http://faostat.fao.org/. Accessed 23 Nov 2016.
Cí·¯ord D, Pearson RA, Archibald RF, Muirhead R. Digestibility and gastro-intestinal transit time of diets containing different proportions of alfalfa and oat straw given to thoroughbreds, Shetland ponies, Highland ponies and donkeys. Anim Sci 1995;61:407–417.
Smith DG, Pearson RA. A review of the factors affecting the survival of donkeys in semi-arid regions of sub-Saharan Africa.. Trop Anim Health Prod 2005 Nov;37 Suppl 1:1-19.
Lee SS, Ha JK, Cheng K. Relative contributions of bacteria, protozoa, and fungi to in vitro degradation of orchard grass cell walls and their interactions.. Appl Environ Microbiol 2000 Sep;66(9):3807-13.
Gruninger RJ, Puniya AK, Callaghan TM, Edwards JE, Youssef N, Dagar SS, Fliegerova K, Griffith GW, Forster R, Tsang A, McAllister T, Elshahed MS. Anaerobic fungi (phylum Neocallimastigomycota): advances in understanding their taxonomy, life cycle, ecology, role and biotechnological potential.. FEMS Microbiol Ecol 2014 Oct;90(1):1-17.
Solomon KV, Haitjema CH, Henske JK, Gilmore SP, Borges-Rivera D, Lipzen A, Brewer HM, Purvine SO, Wright AT, Theodorou MK, Grigoriev IV, Regev A, Thompson DA, O'Malley MA. Early-branching gut fungi possess a large, comprehensive array of biomass-degrading enzymes.. Science 2016 Mar 11;351(6278):1192-5.
Cheng YF, Edwards JE, Allison GG, Zhu WY, Theodorou MK. Diversity and activity of enriched ruminal cultures of anaerobic fungi and methanogens grown together on lignocellulose in consecutive batch culture.. Bioresour Technol 2009 Oct;100(20):4821-8.
Liggenstoffer AS, Youssef NH, Couger MB, Elshahed MS. Phylogenetic diversity and community structure of anaerobic gut fungi (phylum Neocallimastigomycota) in ruminant and non-ruminant herbivores.. ISME J 2010 Oct;4(10):1225-35.
Julliand V, Riondet C, De Vaux A, Alcaraz G, Fonty G. Comparison of metabolic activities between Piromyces citronii, an equine fungal species, and Piromyces communis, a ruminal species. Anim Feed Sci Technol 1998;70:161–168.
Koetschan C, Kittelmann S, Lu J, Al-Halbouni D, Jarvis GN, Müller T, Wolf M, Janssen PH. Internal transcribed spacer 1 secondary structure analysis reveals a common core throughout the anaerobic fungi (Neocallimastigomycota).. PLoS One 2014;9(3):e91928.
Mountfort DO, Asher RA, Bauchop T. Fermentation of Cellulose to Methane and Carbon Dioxide by a Rumen Anaerobic Fungus in a Triculture with Methanobrevibacter sp. Strain RA1 and Methanosarcina barkeri.. Appl Environ Microbiol 1982 Jul;44(1):128-34.
Daly K, Stewart CS, Flint HJ, Shirazi-Beechey SP. Bacterial diversity within the equine large intestine as revealed by molecular analysis of cloned 16S rRNA genes. FEMS Microbiol Ecol 2001;38:141–151.
Hugenholtz P, Goebel BM, Pace NR. Impact of culture-independent studies on the emerging phylogenetic view of bacterial diversity.. J Bacteriol 1998 Sep;180(18):4765-74.
Spring S, Bunk B, Spröer C, Schumann P, Rohde M, Tindall BJ, Klenk HP. Characterization of the first cultured representative of Verrucomicrobia subdivision 5 indicates the proposal of a novel phylum.. ISME J 2016 Dec;10(12):2801-2816.
van Vliet DM, Palakawong Na Ayudthaya S, Diop S, Villanueva L, Stams AJM, Sánchez-Andrea I. Anaerobic Degradation of Sulfated Polysaccharides by Two Novel Kiritimatiellales Strains Isolated From Black Sea Sediment.. Front Microbiol 2019;10:253.
Dojka MA, Hugenholtz P, Haack SK, Pace NR. Microbial diversity in a hydrocarbon- and chlorinated-solvent-contaminated aquifer undergoing intrinsic bioremediation.. Appl Environ Microbiol 1998 Oct;64(10):3869-77.
Stanton TB, Canale-Parola E. Treponema bryantii sp. nov., a rumen spirochete that interacts with cellulolytic bacteria.. Arch Microbiol 1980 Sep;127(2):145-56.
Nakazawa F, Poco SE, Sato M, Ikeda T, Kalfas S, Sundqvist G, Hoshino E. Taxonomic characterization of Mogibacterium diversum sp. nov. and Mogibacterium neglectum sp. nov., isolated from human oral cavities.. Int J Syst Evol Microbiol 2002 Jan;52(Pt 1):115-122.
Nakazawa F, Sato M, Poco SE, Hashimura T, Ikeda T, Kalfas S, Sundqvist G, Hoshino E. Description of Mogibacterium pumilum gen. nov., sp. nov. and Mogibacterium vescum gen. nov., sp. nov., and reclassification of Eubacterium timidum (Holdeman et al. 1980) as Mogibacterium timidum gen. nov., comb. nov.. Int J Syst Evol Microbiol 2000 Mar;50 Pt 2:679-688.
Freier TA, Beitz DC, Li L, Hartman PA. Characterization of Eubacterium coprostanoligenes sp. nov., a cholesterol-reducing anaerobe.. Int J Syst Bacteriol 1994 Jan;44(1):137-42.
Del Dot T, Osawa R, Stackebrandt E. Phascolarctobacterium faecium gen. Nov, spec. Nov., a novel taxon of the Sporomusa group of Bacteria. Syst Appl Microbiol 1993;16:380–384.
Watanabe Y, Nagai F, Morotomi M. Characterization of Phascolarctobacterium succinatutens sp. nov., an asaccharolytic, succinate-utilizing bacterium isolated from human feces.. Appl Environ Microbiol 2012 Jan;78(2):511-8.
Leadbetter JR, Breznak JA. Physiological ecology of Methanobrevibacter cuticularis sp. nov. and Methanobrevibacter curvatus sp. nov., isolated from the hindgut of the termite Reticulitermes flavipes.. Appl Environ Microbiol 1996 Oct;62(10):3620-31.
Henderson G, Cox F, Ganesh S, Jonker A, Young W, Janssen PH. Rumen microbial community composition varies with diet and host, but a core microbiome is found across a wide geographical range.. Sci Rep 2015 Oct 9;5:14567.
Freelove AC, Bolam DN, White P, Hazlewood GP, Gilbert HJ. A novel carbohydrate-binding protein is a component of the plant cell wall-degrading complex of Piromyces equi.. J Biol Chem 2001 Nov 16;276(46):43010-7.
Gaillard-Martinie B, Breton A, Dusser M, Julliand V. Piromyces citronii sp. nov., a strictly anaerobic fungus from the equine caecum: a morphological, metabolic, and ultrastructural study. FEMS Microbiol Lett 1995;130:321–326.
Li J, Heath IB, Bauchop T. Piromyces mae and Piromyces dumbonica, two new species of uniflagellate anaerobic chytridiomycete fungi from the hindgut of the horse and elephant. Can J Bot 1990;68:1021–1033.
Callaghan TM, Podmirseg SM, Hohlweck D, Edwards JE, Puniya AK, Dagar SS. Buwchfawromyces eastonii gen. nov., sp. nov.: a new anaerobic fungus (Neocallimastigomycota) isolated from buffalo faeces. MycoKeys 2015;9:11–28.
van Lingen HJ, Edwards JE, Vaidya JD, van Gastelen S, Saccenti E, van den Bogert B, Bannink A, Smidt H, Plugge CM, Dijkstra J. Diurnal Dynamics of Gaseous and Dissolved Metabolites and Microbiota Composition in the Bovine Rumen.. Front Microbiol 2017;8:425.
Dollhofer V, Callaghan TM, Griffith GW, Lebuhn M, Bauer J. Presence and transcriptional activity of anaerobic fungi in agricultural biogas plants.. Bioresour Technol 2017 Jul;235:131-139.
Ramiro-Garcia J, Hermes GDA, Giatsis C, Sipkema D, Zoetendal EG, Schaap PJ, Smidt H. NG-Tax, a highly accurate and validated pipeline for analysis of 16S rRNA amplicons from complex biomes.. F1000Res 2016;5:1791.
Edwards JE, Hermes GDA, Kittelmann S, Nijsse B, Smidt H. Assessment of the Accuracy of Anaerobic Fungal ITS1 Based Barcoded Amplicon Sequencing for Community Composition Analysis. .
R Core Team. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. 2013.
Neuwirth E. RColorBrewer: ColorBrewer Palettes. R package version 1.1–2. 2014.
Milton Bache S, Wickham H. magrittr: A Forward-Pipe Operator for R. R package version 1.5. 2014.
McMurdie PJ, Holmes S. phyloseq: an R package for reproducible interactive analysis and graphics of microbiome census data.. PLoS One 2013;8(4):e61217.
Zhang Z, Huang B, Gao X, Shi X, Wang X, Wang T, Wang Y, Liu G, Wang C. Dynamic changes in fecal microbiota in donkey foals during weaning: From pre-weaning to post-weaning. Front Microbiol 2023;14:1105330.
Wang X, Wu X, Shang Y, Gao Y, Li Y, Wei Q, Dong Y, Mei X, Zhou S, Sun G, Liu L, Lige B, Zhang Z, Zhang H. High-Altitude Drives the Convergent Evolution of Alpha Diversity and Indicator Microbiota in the Gut Microbiomes of Ungulates. Front Microbiol 2022;13:953234.
Zhang Z, Wang Y, Huang B, Zhu M, Wang C. The Fibrolytic Enzyme Profiles and the Composition of Fungal Communities in Donkey Cecum-Colon Ecosystem. Animals (Basel) 2022 Feb 9;12(4).
Filek K, Trotta A, Gračan R, Di Bello A, Corrente M, Bosak S. Characterization of oral and cloacal microbial communities of wild and rehabilitated loggerhead sea turtles (Caretta caretta). Anim Microbiome 2021 Sep 3;3(1):59.
Yanez-Montalvo A, Gaona O, Águila B, Arias-Domínguez N, Falcón LI, Pérez-Flores J. Tapirus bairdii-Associated Fecal Microbiome from a Critical Conservation Area: Calakmul, México. Curr Microbiol 2021 Jul;78(7):2648-2659.
Rojas CA, Ramírez-Barahona S, Holekamp KE, Theis KR. Host phylogeny and host ecology structure the mammalian gut microbiota at different taxonomic scales. Anim Microbiome 2021 Apr 23;3(1):33.
Gilyazova I, Korytina G, Kochetova O, Savelieva O, Mikhaylova E, Vershinina Z, Chumakova A, Markelov V, Abdeeva G, Karunas A, Khusnutdinova E, Gusev O. Advances in Genomics and Postgenomics in Poultry Science: Current Achievements and Future Directions. Int J Mol Sci 2025 Aug 26;26(17).
Li Y, Zhou H, Yu J, Dong B, Li H, Zhang C, Zhang G, Guo C. Dietary protein sources in concentrate supplementation influence growth performance by manipulating gut microbiota and serum metabolites in suckling Donkey foals. Anim Microbiome 2025 Aug 26;7(1):91.
Arnalot L, Pascal G, Cauquil L, Vanbergue E, Foucras G, Zened A. The bacterial faecal microbiota shifts during the transition period in dairy cows. Anim Microbiome 2025 Jul 24;7(1):79.
Wang Y, Shi M, Wu J, Han X, Li M, Wu Y, Jiang Y, Zhang H, Liu S, Hu D. Variations in Intestinal Microbiota Among Three Species in the Cervidae Family Under the Same Feeding Conditions. Vet Sci 2025 May 3;12(5).
Deng X, Li H, Wu A, He J, Mao X, Dai Z, Tian G, Cai J, Tang J, Luo Y. Composition, Influencing Factors, and Effects on Host Nutrient Metabolism of Fungi in Gastrointestinal Tract of Monogastric Animals. Animals (Basel) 2025 Mar 1;15(5).
Kou X, Ma Q, Liu Y, Khan MZ, Wu B, Chen W, Liu X, Wang C, Li Y. Exploring the Effect of Gastrointestinal Prevotella on Growth Performance Traits in Livestock Animals. Animals (Basel) 2024 Jul 2;14(13).
Mikkelsen D, McGowan AM, Gibson JS, Lanyon JM, Horsman S, Seddon JM. Faecal bacterial communities differ amongst discrete foraging populations of dugongs along the east Australian coast. FEMS Microbiol Ecol 2024 May 14;100(6).
Shen H, Wang T, Dong W, Sun G, Liu J, Peng N, Zhao S. Metagenome-assembled genome reveals species and functional composition of Jianghan chicken gut microbiota and isolation of Pediococcus acidilactic with probiotic properties. Microbiome 2024 Feb 12;12(1):25.
Pohlin F, Frei C, Meyer LCR, Roch FF, Quijada NM, Conrady B, Neubauer V, Hofmeyr M, Cooper D, Stalder G, Wetzels SU. Capture and transport of white rhinoceroses (Ceratotherium simum) cause shifts in their fecal microbiota composition towards dysbiosis. Conserv Physiol 2023;11(1):coad089.
Klinsawat W, Uthaipaisanwong P, Jenjaroenpun P, Sripiboon S, Wongsurawat T, Kusonmano K. Microbiome variations among age classes and diets of captive Asian elephants (Elephas maximus) in Thailand using full-length 16S rRNA nanopore sequencing. Sci Rep 2023 Oct 17;13(1):17685.
Baniel A, Amato KR, Beehner JC, Bergman TJ, Mercer A, Perlman RF, Petrullo L, Reitsema L, Sams S, Lu A, Snyder-Mackler N. Seasonal shifts in the gut microbiome indicate plastic responses to diet in wild geladas. Microbiome 2021 Jan 23;9(1):26.
Tassone S, Fortina R, Valle E, Cavallarin L, Raspa F, Boggero S, Bergero D, Giammarino M, Renna M. Comparison of In Vivo and In Vitro Digestibility in Donkeys. Animals (Basel) 2020 Nov 12;10(11).
Hess M, Paul SS, Puniya AK, van der Giezen M, Shaw C, Edwards JE, Fliegerová K. Anaerobic Fungi: Past, Present, and Future. Front Microbiol 2020;11:584893.