To read the full-text of this research, you can request a copy directly from the author.
Gruby and Delafond  discovered the rumen protozoa in 1843 and suggested that their digestive activity was the primary means by which ruminants could survive on an all-plant diet. However, subsequent studies have clearly shown that bacteria actually play a prominent role in the fermentation of plant materials, and fungi are also involved [8, 13, 20].
To read the full-text of this research, you can request a copy directly from the author.
... Daily effluent samples (100 mL/sample) were taken inside of each vessel for protozoal count during the 3-d collection period immediately before the 1030 h feeding. Vessel protozoal cell counts were completed using the Sedgewick-Rafter chamber by Dehority (2005). A 50-mL sample of effluent was also collected on the 3 collection days and strained through 8 layers of cheesecloth. ...
A continuous-culture fermentor study was conducted to assess nutrient digestibilities, volatile fatty acid (VFA) concentrations, microbial protein synthesis, bacterial nitrogen (N) efficiency, and enteric methane (CH4) production of four 50:50 grass-legume diets, randomly assigned in a 4 × 4 Latin square design. Four legumes with different concentrations of condensed tannins (CT) were tested: alfalfa [ALF; Medicago sativa L., non-CT legume]; birdsfoot trefoil [BFT; Lotus corniculatus L., low-CT legume]; crown vetch [CV; Securigera varia (L.) Lassen, moderate-CT legume]; and sericea lespedeza [SL; Lespedeza cuneata (Dum. Cours.) G. Don, high-CT legume]. Orchardgrass (Dactylis glomerata L.) was the common forage used in all diets. Four fermentors were evaluated over four 10-d periods by feeding 82 g of dry matter (DM)/d in 4 equal feedings. Methane output was recorded every 10 min. Effluent samples were collected during the last 3 d of the experiment, composited by fermentor and period, and analyzed for pH and VFA, as well as DM, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber for determination of apparent and true nutrient digestibilities. Microbial protein synthesis and bacterial efficiency were estimated by analysis of N flows and purines. The CT concentrations were 3, 21, 38 and 76 g/kg of DM for ALF, BFT, CV, and SL diets, respectively. The SL diet had decreased fiber digestibilities and total VFA concentrations compared with the other diets. This resulted in the least total CH4 production in the SL diet. Bacterial N efficiency per kilogram of organic matter truly digested was lower in the SL diet than in the BFT and CV diets. The lowest CH4 production per unit of digestible nutrients was also found in the SL diet. Further work should be conducted to find optimal diets (by testing other legumes, rations, and sources of CT) for reducing CH4 emissions without negatively affecting ruminal digestion to maintain or improve productivity.
... Daily DM and protozoal samples were taken from each vessel using a 10-mL graduated pipette. The tip of the pipette was removed to allow large digesta particles to freely flow into the pipette (Dehority, 2005). Samples were taken just prior to the 10:30 hours feeding, and 60 ml of sample was collected from the vessel. ...
A 4‐unit, single‐flow continuous culture fermenter system was developed to assess in vitro nutrient digestibility, volatile fatty acid (VFA) concentration and daily enteric methane (CH4) production of ruminant diets. The objective was to develop a closed‐vessel system that maintained protozoal populations and provided accurate predictions of total CH4 production. A diet of 50% orchardgrass (Dactylis glomerata L.) and 50% alfalfa (Medicago sativa L.) was fed during 4, 10‐day periods (7‐day adaptation and 3‐day collection). Fermenters were fed 82 g of dry matter (DM)/day in four equal feedings. pH and temperature were taken every 2 min, and CH4 concentration was measured every 10 min. Samples for DM and protozoal counts were taken daily, and daily effluent samples were collected for determination of DM, VFA and NH3‐N concentrations. There was no effect (p > 0.17) of adaptation versus collection days on vessel and effluent DM, temperature or pH. Initial protozoal counts decreased (p < 0.01), but recovered to initial counts by the collection period. Total VFA, acetate, propionate and isobutyrate concentrations did not differ (p ≥ 0.13) among periods or days of the collection period. There was no difference (p ≥ 0.37) among days or periods in total daily CH4 production and CH4 production per g of OM, NDF, digestible OM or digestible NDF fed. Data collected throughout 4 experimental periods demonstrated that the system was able to reach a steady state in fermentation well within the 7‐day adaptation period and even typically variable data (i.e., CH4 production) were stable within and across periods. While further research is needed to determine the relationship between this system and in vivo data, this continuous culture fermenter system provides a valid comparison of in vitro ruminal fermentation and enteric CH4 production of ruminant diets that can then be further validated with in vivo studies.
... The protozoal cells in the culture samples were counted under a microscope as done previously . Briefly, each of the collected protozoal samples was fixed in 16.7% formalin, diluted with glycerol (10% final concentration), and dyed with a brilliant green dye solution (0.2% (w/v) brilliant green, 0.2% (v/v) glacial acetic acid) (Dehority, 2005). Then, the protozoal cells were counted using a Sedgewick-Rafter counting chamber (Thomas Scientific, Swedesboro, NJ) under 100× magnification. ...
Rumen protozoa, primarily ciliates, are one of the important groups of strictly anaerobic microbes living in the rumen. Despite their ubiquitous occurrence in the rumen and significant contribution to host animals, it is still poorly understood why they live only in the rumen and similar environment. Because rumen protozoa require strict anaerobic conditions to sustain their viability and grow, only a few laboratories equipped with protozoology expertise and anaerobic facilities can grow rumen protozoa in laboratory. Also for the same reason, only a few species have been grown and maintained as laboratory cultures for research. Prompted by a recent study, we hypothesized that anaerobic rumen protozoa could also be cultivated aerobically if antioxidants were included in the media. Indeed, our experiments showed that the cultures of both Entodinium caudatum and Epidinium caudatum, two major rumen protozoal species, could be cultured successfully in aerobic media supplemented with ascorbic acid, glutathione and α-ketoglutarate as antioxidants. Anaerobic fermentation was maintained through the fermentation characteristics and microbial populations were altered to some extent under aerobic conditions. The antioxidants also enhanced the revival of cryopreserved stock cultures of both rumen protozoal species. The results of this study may facilitate and promote future research in which rumen protozoa need to be cultured in laboratory.
... Rumen protozoa, exclusively ciliates, rank second only to bacteria in cellular biomass of the ruminal microbiota. They are only found in the rumen and similar habitats (Dehority, 1986(Dehority, , 2005 where they play important roles in feed digestion and homeostasis of the rumen ecosystem (Firkins et al., 2007;Newbold et al., 2015). However, they are also blamed for promoting methane (CH 4 ) emission due to their mutualistic relationship with methanogens by producing hydrogen (Newbold et al., 1995). ...
Ruminal ciliates both preys on and form symbiotic relationships with other members of the ruminal microbiota for their survival. However, it remains elusive if they have selectivity over their preys or symbionts. In the present study, we investigated the above selectivity by identifying and comparing the free-living prokaryotes (FLP) and the ciliate-associated prokaryotes (CAP) using Illumina MiSeq sequencing of 16S rRNA gene amplicons. We used single ciliates cells of both monocultures of Entodinium caudatum and Epidinium caudatum and eight different ciliate genera isolated from fresh rumen fluid of dairy cows. Irrespective of the source (laboratory monocultures vs. fresh isolates) of the single ciliate cells, the CAP significantly differed from the FLP in microbiota community profiles. Many bacterial taxa were either enriched or almost exclusively found in the CAP across most of the ciliate genera. A number of bacteria were also found for the first time as ruminal bacteria in the CAP. However, no clear difference was found in methanogens between the CAP and the FLP, which was confirmed using methanogen-specific qPCR. These results suggest that ruminal ciliates probably select their preys and symbionts, the latter of which has rarely been found among the free-living ruminal prokaryotes. The bacteria enriched or exclusively found in the CAP can be target bacteria to detect and localize using specific probes designed from their 16S rRNA sequences, to characterize using single-cell genomics, or to isolate using new media designed based on genomic information.
... Microbial abundances: Samples for protozoa counting were mixed with 9% formaldehyde and preserved at -4°C, then counted in a haemacytometer under light microscope (Nikon YS100, Nikon, Yokohama, Japan) using the method of Dehority (2005). Group-specific primers for methanogens (mcrA), total bacteria and anaerobic fungi, and species-specific primers for R. flavefaciens and F. succinogenes are listed in Table 1, as described by Denman and McSweeney (2006) and Denman et al. (2007). ...
The study aimed to investigate the effects of gynosaponin on in vitro methanogenesis under different forage-concentrate ratios (F:C ratios). Experiment was conducted with two kinds of F:C ratios (F:C = 7:3 and F:C = 3:7) and gynosaponin addition (0 mg and 16 mg) in a 2×2 double factorial design. In the presence of gynosaponin, methane production and acetate concentration were significantly decreased, whereas concentration of propionate tended to be increased resulting in a significant reduction (p<0.05) of acetate:propionate ratio (A:P ratio), in high-forage substrate. Gynosaponin treatment increased (p<0.05) the butyrate concentration in both F:C ratios. Denaturing gradient gel electrophoresis (DGGE) analysis showed there was no apparent shift in the composition of total bacteria, protozoa and methanogens after treated by gynosaponin under both F:C ratios. The real-time polymerase chain reaction (PCR) analysis indicated that variable F:C ratios significantly affected the abundances of Fibrobacter succinogenes, Rumninococcus flavefaciens, total fungi and counts of protozoa (p<0.05), but did not affect the mcrA gene copies of methanogens and abundance of total bacteria. Counts of protozoa and abundance of F.succinogenes were decreased significantly (p<0.05), whereas mcrA gene copies of methanogens were decreased slightly (p<0.10) in high-forage substrate after treated by gynosaponin. However, gynosaponin treatment under high-concentrate level did not affect the methanogenesis, fermentation characteristics and tested microbes. Accordingly, overall results suggested that gynosaponin supplementation reduced the in vitro methanogenesis and improved rumen fermentation under high-forage condition by changing the abundances of related rumen microbes.
The aim of the present study was to investigate the beneficial effects of dietary supplementation with oil palm frond (leaf) (OPF) with and without oil palm meal (OPM) on nutrient intake and digestibility, ruminal fermentation and growth performance in goats.
Six female crossbred goats were fed for 28 days of 3 diet treatments; 100 % para-grass (T1); 50 % para-grass + 50 % OPF (T2), and 30 % para-grass + 50 % OPF + 20 % OPM (T3). Body weight, rectal temperature (RT), respiratory rate (RR) and urine volume, food intake (FI), dry matter intake (DMI) and water intake (WI) were measured daily. Nutrient digestibility was determined from five consecutive days of last week in each diet. Ruminal fluid, urine and blood were collected at the end for determination of rumen protozoa and VFA contents, urinary allantoin excretion, blood cell count and chemistry profiles.
Goats fed T2 and T3 showed higher dry matter and nutrients intakes while protein digestibility was suppressed compared with those for T1. Crude fat digestibility declined in T2 but maintained after adding the OPM (T3). High fat intake by giving OPF and OPM corresponded to a higher ruminal acetate/propionate ratio (C2/C3) and serum cholesterol level. An increased urinary allantoin/creatinine ratio was found in T2 and T3 compared with T1, implying an increased number of ruminal microbes.
Increased dry matter intake in T2 and T3 suggested that oil palm by-products are partly useful as a replacement for para-grass in goats. Replacement with the by-products increased plasma cholesterol level, which suggested that these products are a useful energy source. Changes in rumen parameters suggested an increased microbial number and activity suitable for acetate production. However, the limited digestibility of protein implies that addition of high protein feeds may be recommended to increase body weight gain of goats.
An in vitro gas production technique was used to study the effect of jojoba meal on gas production, rumen fermentation, true dry and organic matter digestibility, the activity of amylase and carboxymethyl cellulase (CMCase) and protozoa count. Jojoba meal was added to a concentrate diet at 6%, 9% and 18% levels, substituting for cottonseed meal. A gas production technique was performed using rumen fluid collected from three fistulated Santa Ines sheep. Cumulative gas production was recorded at 3, 6, 9, 12, 24, 48, 72 and 96 h of incubation time. Kinetics of gas production was fitted to an exponential model. Volatile fatty acids (VFA), Ammonia-N (NH3-N) concentrations, true dry and organic matter degradability and enzyme activity (CMCase and amylase) were determined at 24 h of incubation time. The cumulative volume of gas production was increased by adding jojoba meal. Total gas produced at 96 h of incubation time was higher for the first level of jojoba meal. The values of iso-butyrate, butyrate and iso-valerate were significantly decreased for control sample compared to the third level of jojoba meal. No significant effects of jojoba meal on acetate, propionate and valerate concentration were seen. Also, no significant effects were observed on CH4, NH3-N levels or true dry and organic matter degradability at 24 h of incubation time. pH value was significantly decreased at the third level of jojoba. No significant effects of jojoba meal were observed on the specific activity of amylase in the supernatant of sonicated bottle contents, while the specific activity of CMCase was significantly decreased. The lowest protozoa count was at the third level of jojoba meal.
Wild-type strains of the protozoan ciliate Euplotes collected from different locations on the coasts of Antarctica, Tierra del Fuego and the Arctic were taxonomically identified as the morpho-species Euplotes nobilii, based on morphometric and phylogenetic analyses. Subsequent studies of their sexual interactions revealed that mating combinations of Antarctic and Arctic strains form stable pairs of conjugant cells. These conjugant pairs were isolated and shown to complete mutual gene exchange and cross-fertilization. The biological significance of this finding was further substantiated by demonstrating that close homology exists among the three-dimensional structures determined by NMR of the water-borne signaling pheromones that are constitutively secreted into the extracellular space by these interbreeding strains, in which these molecules trigger the switch between the growth stage and the sexual stage of the life cycle. The fact that Antarctic and Arctic E. nobilii populations share the same gene pool and belong to the same biological species provides new support to the biogeographic model of global distribution of eukaryotic microorganisms, which had so far been based exclusively on studies of morphological and phylogenetic taxonomy.
In a survey of rumen contents from 30 adult Turkish domestic cattle (Bos taurus L.), an unusual new form of Eudiplodinium was observed. This form was established as a new species, Eudiplodinium dehorityi n.sp., and constituted 13.31, 15.41, 0.20 and 0.34% of the total ciliates in four animals. Several morphological characteristics of this species are unique to the genus Eudiplodinium, showing definite evolutionary trends to the genera Elytroplastron and Polyplastron.
The present study aimed at the long-term storage of rumen protozoa as living cells in liquid nitrogen. The two-step or interrupted
slow freezing procedure was used to cryopreserve six of the dominant species of rumen ciliates isolated from monofaunated
animals, Dasytricha ruminantium, Entodinium caudatum, Epidinium ecaudatum caudatum, Eudiplodinium maggii, Isotricha prostoma, and Polyplastron multivesiculatum. We optimized the first step in the interrupted slow freezing procedure, from the extracellular ice nucleation temperature
to the holding temperature, and studied the effects of the cooling rates on survival. In addition to the nature of the cryoprotectant
(dimethyl sulfoxide), the equilibration temperature and equilibration time (25°C and 5 min, respectively), and the holding
time at subzero temperature (45 min) recommended previously (S. Kišidayová, J. Microbiol. Methods 22:185-192, 1995), we found that a holding temperature of −30°C, a cooling rate from extracellular ice nucleation temperature
to holding temperature of between 1.2°C/min and 2.5°C/min, depending on the ciliate, and rumen juice as the freezing and thawing
medium markedly improved the survival rate. Survival rates determined after 2 weeks in liquid nitrogen were 100% for Isotricha, 98% for Dasytricha, 85% for Epidinium, 79% for Polyplastron, 63% for Eudiplodinium, and 60% for Entodinium. They were not significantly modified after a period of 1 year in liquid nitrogen. Four of the five ciliate species cryopreserved
for 8 months in liquid nitrogen successfully colonized the rumen when inoculated into defaunated animals. These results have
made it possible to set up a bank of cryopreserved rumen protozoa.
All ruminants are dependent on the microorganisms that live in their forestomach - the rumen - to break down ingested feed constituents into a form that the host animal can utilize. Protozoa are part of this complex ruminal population and are essential for the nutritional well-being and productivity of the host ruminant. Over 30 different genera (nearly 300 species) of protozoa from the rumen ecosystem have been described since their initial discovery nearly 150 years ago. This book brings together, for the first time, the available information on these protozoa. It comprehensively describes the characteristic anatomical features of value for their identification and includes detailed sections on techniques and methodologies for the isolation and cultivation of these fastidious, oxygen-sensitive microorganisms. Their occurrence, biochemistry, physiology, and role in the ruminal ecosystem are fully reviewed. Particular emphasis is given to potential improvement of the nutrition and productivity of the host ruminant through manipulation of the protozoal population and its activities.
Daily infusion of 7, 35, and 70 g of glucose m solution (1, 5, and 10 per cent. of the ration) into the rumen of Merino sheep maintained on an adequate diet resulted in the ruminal pH falling 2–4 hr after feeding, from a mean of 5.66 without added glucose to 5.40 at the higher glucose levels. The concentration of ammonia also decreased, whereas that of volatile fatty acids increased. At the 10 per cent. glucose level, food intake was depressed and the ruminal pH in this treatment did not fall below that at the 5 per cent. glucose level. A significant daily fall in the ruminal pH minima was found during the 3-day sampling period. No consistently significant differences in the concentration of ciliate Protozoa were found at four different sites in the rumen, either before or 1 hr after feeding, although there were significant differences between sheep. Samples taken from the bottom of the rumen immediately inferior to the ruminal cannula, before feeding and 1, 2, 4, 6, 8, 12, and 16 hr after feeding, showed: (a) Only oligotrichs in the ciliate population; (b) Marked diurnal fluctuation in the ciliate population, the concentration after feeding falling to as low
as one-third of the prefeeding levels; (c) A diurnal cycle for dividing Protozoa which indicated that their capacity to multiply was strongly inhibited by the low pH experienced 2–4 hr after feeding. A depression of the average ciliate concentration daily during the 3-day sampling period was also demonstrated. This was related to a consistent but inexplicable fall in the daily ruminal pH minima over this period. It was concluded that the minimum pH within the rumen is an important factor controlling rumen protozoal concentrations in the sheep, and the need for cognizance of this phenomenon in studies of rumen Protozoa is stressed.
Occurrence of protozoa in the digestive tract of herbivores is dependent upon the occurrence of an environmentally compatible section of the tract and a retention time for gut contents in that section which exceeds the protozoan generation time. In general, herbivores can be classified as pre-gastric (foregut) or post-gastric (hindgut) fermentors. Fermentation in the foregut has evolved through enlargement of the stomach in some way to slow down ingesta passage rate and provide physical separation of the ingesta from the acid-secreting regions, as well as an adequate production of buffered saliva. Hindgut fermentations occur in the caecum-proximal colon area. Most of the protozoa in the digestive tract of herbivorous mammals belong to the class Kinetofragminophorea in the orders Prostomatida, Trichostomatida and Entodiniomorphida. They are anaerobic, live in conjunction with a large bacterial population and can ferment the structural polysaccharides of plants. End products of protozoal fermentation are similar to those of the bacterial population, i.e. volatile fatty acids, lactic acid, carbon dioxide and hydrogen. Additional products of the fermentation are vitamins and microbial protein which are subsequently utilized by foregut fermentors, whereas these products are essentially lost in hindgut fermentors unless they practice coprophagy. Only limited information is available on digestive and metabolic pathways of the gut protozoa, primarily because of our inability to grow them in axenic culture. Specific faunas appear to be associated with site of fermentation, animal species and diet. Diet in turn can affect pH and contents turnover time, both of which are very important in the establishment and growth of a protozoan population in the digestive tract.
Samples of rumen contents were obtained from 6 pronghorn antelope, 7 mule deer, 1 white-tailed deer and 2 elk living in the northwestern United States. Four of the pronghorn antelopes were protozoa free. Of the two remaining animals, each contained a single species of Entodinium, E. dubardi or E. ovibos. Protozoa were present in rumen contents from six of the seven mule deer. All protozoa were identified as E. dubardi or E. dubardi types, except for a new form of E. quadricuspis which was observed in three animals. The single sample of rumen contents from a white-tailed deer contained over 99% E. dubardi types plus Eudiplodinium impalae. A diverse fauna of ophryoscolecid protozoa occurred in both elk. A new species of Entodinium, E. wapiti n. sp., was observed in rumen contents from one of the elk. Protozoal numbers per ml of rumen contents ranged from 11.5×104 in one of the mule deer to 105.4×104 in the white-tailed deer. Several of the protozoal species found in these animals are more commonly associated with Arctic ruminants.
Composition of rumen ciliate fauna in five Zambian, sassaby antelopes was determined. Six genera, 18 species, and four forms were identified. One new species and form, belonging to the subfamily Diplodiniinae, were found, then labeled Ostracodinium damaliscus n. sp. and Diplodinium bubalidis f. aspinosum n. f., respectively. Only ophryoscolecid species were present while isotrichids were absent. Twelve of 18 total species are commmonly found in African antelopes. Three of those 12 species, Entodinium fyferi, Enoploplastron garstangi and Opisthotrichum janus, are only found in African antelopes. Percentage composition was low in the genera ml of rumen fluid, and the average number of ciliate species per host was 17.2.
The rumen flagellat Piromonas communis is the zoospore of a phycomycete fungus inhabiting the rumen. Zoosporogenesis was stimulated by a dietary component (the inducer), and inhibited by compounds affecting membrane structure and function, but not by inhibitors of protein synthesis. The zoospores showed taxis towards the tissues surrounding the inflorescence of Lolium perenne L. in the rumen, invading principally the stomata and damaged tissues. The zoospores germinated on this substratum and the rhizoids of the developing vegetative stage penetrated the tissue, taking up C14 from labelled plant material, which was incorporated into the fungal cells. The conditions for maximum flagellate production (39 degrees C, pH 6-0 to 7-0, high concentration of CO2, absence of O2) resembled those found in the rumen. The organism was cultured in an undefined medium in vitro in the absence of other flagellates.
Thirty-two strains of pectin-fermenting rumen bacteria were isolated from bovine rumen contents in a rumen fluid medium which contained pectin as the only added energy source. Based on differences in morphology and the Gram stain, 10 of these strains were selected for characterization. Two strains were identified as Lachnospira multiparus, four strains were identified as Butyrivbrio fibrisolvens, and three strains were identified as Bacteroides ruminicola. Characteristics of the remaining strain did not correspond with any previously described species. It was a gram-positive anaerobic coccus, 1.0 to 1.2 mum in diameter, and occurred primarily as single cells or diplococci. The strain fermented pectin rapidly but showed little or no growth on any other energy sources tested. The only detectable end products were acetic acid and gas, a portion of which was identified as hydrogen. Although the physiological characteristics of this organism differ markedly from other described species, it has been placed in the genus Peptostreptococcus on the basis of morphology, Gram stain, relations to oxygen, and the occurrence of cell division in only one plane. End products of fermentation are somewhat similar to those of the cellulolytic ruminococci. Eight previously characterized strains of cellulolytic bacteria isolated in nonselective media were unable to ferment pectin, whereas ten strains of hemicellulolytic rumen bacteria, eight of which were isolated with a xylan medium, showed considerable variation in this characteristic.
Total numbers of protozoa can be significantly lower in rumen fluid than in whole rumen contents, depending on the time of sampling and the procedure used to separate the fluid and solid fractions. Moreover, generic distribution in rumen fluid was significantly affected in all cases tested. The percentage of Entodinium spp. increased, whereas percentages of Diplodinium spp. and Ophryoscolex spp. decreased. Microscopic observation of fresh and fixed rumen contents did not indicate any marked attachment of protozoa to particulate matter. In addition, dilution of whole rumen contents with water, 5 mM sucrose, or 0.1% Tween 80 before fixation did not affect total numbers or generic composition of protozoa. It was thus concluded that attachment to feed particles is probably not a problem in counting procedures. Blending of whole rumen contents to facilitate subsampling caused a decrease in numbers of protozoa. The concentration of formaldehyde used for preservation of rumen contents, 4, 10, or 18.5%, did not affect the total count.
Generation times were determined in vitro with a pure culture of Epidinium caudatum and a mixed culture of Epidinium caudatum and Entodinium caudatum. Measurement of logarithmic growth from a small inoculum for Epidinium caudatum alone, or in coculture, resulted in generation times of 30.8 and 19.5 h, respectively. Epidinium concentrations, either alone or in coculture, were maintained when cultures were transferred every 12 h; however, concentrations decreased rapidly with transfers at 4, 6, or 8 h. For Entodinium caudatum, a generation time of 16.3 h was obtained from measurement of logarithmic growth. Based on sequential transfer data at varying time intervals, Epidinium caudatum and Entodinium caudatum seem to be capable of doubling in approximately 12 to 13 h. These values are markedly less than those previously reported and help explain the ability of these protozoa to maintain themselves in the rumen.
Rumen ciliate species composition was surveyed in domestic yaks kept in Tibet, Sichuan, and Inner Mongolia, China. Twelve genera including 36 species with 18 formae were identified. The species compositions were slightly different among the three areas: yaks in Tibet had the simplest fauna, in contrast, the fauna of yaks in Inner Mongolia were the most abundant and similar to those found in the cattle kept in the same area. This suggests that the rumen ciliate composition of yaks is affected by that of cattle kept together or in proximity. A new species belonging to the genus Entodinium, Entodinium monuo n. sp., was recognized from the yaks in all areas. This new species was common in the yaks but was not detected in the cattle fed near yaks in Inner Mongolia. There was a similar generic ciliate composition in yaks kept in respective areas. Entodinium was the most predominate ciliate (51.9-61.0%) with total ciliate densities estimated as 10(5)/ml per yak.