Ruminal Microbial Populations Research Articles

Effects of dietary energy levels on rumen bacterial community composition in Holstein heifers under the same forage to concentrate ratio condition

BackgroundThe rumen bacterial community plays a critical role in feeds degradation and productivity. The effects of different forage to concentrate ratios on the ruminal microbial population structure have been studied extensively; however, research into changes in the ruminal bacterial community composition in heifers fed different energy level diets, with the same forage to concentrate ratio, has been very limited. The purpose of this study was to investigate the effects of different dietary energy levels, with the same forage to concentrate ratio, on ruminal bacterial community composition of heifers. Furthermore, we also determine the relationship between rumen bacteria and ruminal fermentation parameters.ResultsThe 16S rRNA gene sequencing showed that, under the same forage to concentrate ratio of 50:50, an 8% difference in dietary energy level had no significant impact on the alpha diversity and the relative abundance of the major phyla and most of the major genera in heifers. In all the treatments groups, Firmicutes, Bacteroidetes, and Proteobacteria were the dominant phyla. Spearman correlation analysis between the relative abundances of the rumen bacteria at the genus level and the fermentation parameters showed that the relative abundances of Prevotella and BF311 were positively correlated with the ammonia nitrogen and butyrate concentrations, and these two genera were negatively correlated with the propionate and isovalerate concentrations, respectively, and the genus Bifidobacterium was positively correlated with the butyrate concentration and was negatively correlated with propionate and isovalerate concentration. The total volatile fatty acid concentration was positively correlated with BF311 abundances, and was negatively correlated with Trichococcus and Facklamia abundances.ConclusionsUnder the same forage to concentrate ratio condition of 50:50, an 8% difference in dietary energy levels had little impact on rumen bacterial community composition in heifers. The correlations between some genera of ruminal bacteria and the concentrations of volatile fatty acids and ammonia nitrogen might be indicative that the ruminal fermentation parameters are strongly influenced by the rumen bacterial community composition.

Effects of Matricaria chamomille and Cichorium intybus powder on Performance, Rumen Microbial Population and Some Blood Parameters of Dallagh Sheep

BACKGROUND: Manipulation of rumen microbial population for improving animal performance is done by several methods including medicinal plants. Matricaria chamomille (chamomile) and Cichorium intybus (chicory) are two medicinal plant with antibacterial effect that there is little information about the effects of them on rumen microflora. OBJECTIVE: The present study was carried out to evaluate the effects of chamomile and chicory powder on performance, ruminal microbial population and some blood parameters of sheep. METHODS: 9 Dallagh sheep were used in a change over design experiment at three 21-d periods (14 days as adaptation and 7 days for sample collection). Treatments were: 1) control )without additive(, 2) chamomile ( contained 10% chamomile powder) and 3) chicory (contained %10 chicory powder). Rumen fluid was collected before, 4 h and 8 h after morning feeding and a blood sample was obtained 3 h after morning feeding at last day of each period. RESULTS: Weight gain, dry matter intake, feed conversion ratio, total count of bacteria, acid lactic bacteria, rumen pH, blood glucose and total protein were not affected by treatments. Diet containing 100g chicory significantly decreased plasma triglyceride versus chamomile but the difference was not significant compared with control. Coliforms in rumen fluid at 4 hours after morning feeding were lower in chamomile treatment than control (P<0.05). Lambs received chamomile and chicory powder had significantly higher Rumen protozoa number before morning feeding. In conclusion, although Matricaria chamomille and Cichorium intybus dry powder had some significant effects on rumen microbial population but had no effect on performance, growth and blood metabolites.

257 Ruminal volatile fatty acid concentration and microbial populations as a proxy for of feed efficiency in beef steers

257 Ruminal volatile fatty acid concentration and microbial populations as a proxy for of feed efficiency in beef steers

Effect of sugarcane fiber digestibility, conservation method and concentrate level on the ruminal ecosystem of beef cattle

The aim of this study was to investigate the effects of sugarcane neutral detergent fiber digestibility (NDFD), conservation method, and concentrate level on the ruminal microbial population of steers. Eight ruminal-cannulated Nellore steers were distributed in two contemporary 4 × 4 Latin Square design with a 2 × 2 factorial arrangement of treatments. Experiment 1: diets were formulated with 60% of concentrate level, and two sugarcane genotypes (high or low NDFD) either freshly cut or as silage. Experiment 2: diets were formulated with two levels of concentrate (60 or 80%), and two sugarcane genotypes (high or low NDFD) offered as freshly cut. Each experimental period lasted for 14 d, with the last 4 d used for ruminal fluid collection. Three cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus albus, Ruminococcus flavefaciens), two amylolytic (Streptococcus bovis, Ruminobacter amylophilus), and a lactate fermenting microorganism (Megasphaera elsdenii) were quantified by qPCR. Experiment 1: diets with fresh sugarcane increased the population of S. bovis, and M. elsdenii. Sugarcane with high NDFD increased F. succinogenes population only when sugarcane was offered as freshly cut. Experiment 2: increasing concentrate in the diet decreased S. bovis population, and increased R. amylophilus. Sugarcane with high NDFD increased the population of cellulolytic bacteria only at the 60% concentrate diet. Providing sugarcane with high NDFD favored the growth of fibrolytic bacteria, and this effect were dependent on the conservation method and on diet concentrate level. In addition, sucrose appears to have great effect on the composition of ruminal microflora, especially S. bovis.

Analysis of selected rumen microbial populations in dairy heifers limit fed diets varying in trace mineral form and starch content

Eight rumen-cannulated Holstein heifers were used to explore the effect of trace mineral form and diet starch content on selected ruminal microbial populations under limit feeding conditions. Heifers were subjected to a split-plot, 4×4 Latin square design with 19-day periods. Trace mineral form [organic proteinates (OTM) or inorganic sulfates (ITM)] was the whole-plot factor, and starch content (3.5%, 12.9%, 22.3%, and 31.7% DM) was the sub-plot factor. Rumen samples were collected 3h after feeding on day 18 of each period, and DNA was extracted. Relative abundances of 6 well-studied bacterial taxa, total anaerobic fungi, ciliate protozoa, methanogenic Archaea and bacteria were determined using validated primer sets by real-time quantitative PCR. Targeted populations had relative abundances comparable to those previously reported. Of the microbial populations measured, trace mineral form influenced only Prevotella bryantii, which was increased by OTM. Increasing dietary starch concentration linearly decreased methanogenic Archaea, total bacteria, Prevotella spp., and Prevotella bryantii, and tended to linearly decrease fungi and protozoa. In conclusion, contrary to the starch content, trace mineral form had limited impact on the abundance of selected microbial populations in limit fed heifers 3h after feeding. The unexpected effect of starch content on bacterial populations and protozoa could be the result of different eating patterns of heifers fed diets varying in starch content.

Peppermint and Pennyroyal Essential Oil Effect on Performance, Rumen Microbial Population and Some Blood Parameters of Sheep

BACKGROUND: The use of antibiotics as feed additive in animal feeds due to the appearance of residues in milk and meat and their effects on human health has restricted. Two of essential oils with high potential for use in ruminant diet are Mentha piperita (peppermint) and Mentha pulegium (pennyroyal) essential oil. OBJECTIVE: This study was conducted to investigate the effects of essential oils of peppermint and pennyroyal on performance, ruminal microbial population and some blood parameters of sheep. METHODS: For this purpose, 9 Dallagh sheep were used in a change over design experiment at three 21-d periods (14 days as adaptation and 7 days for sample collection). Experimental treatments were 1) basal diet without additive (control), 2) basal diet + 110 mg/d Mentha piperita essential oil and 3) basal diet +110 mg/d Mentha pulegium essential oil. Sheep were kept in individual cages and had free access to food and water. Rumen fluid was collected before, 4 h and 8 h after morning feeding and a blood sample was obtained 3 h after morning feeding at last day of each period. RESULTS: Essential oils had no effect on performance, blood parameters, pH, ammonia, protozoa, and total viable bacterial count of rumen. Coliforms of rumen fluid significantly decreased at 4 h and increased 8 h after morning feeding following peppermint and pennyroyal supplementation, respectively (P<0.05). Acid lactic bacteria count was significantly higher at before and 4 h after morning feeding in pennyroyal treatment compared with other treatments. CONCLUSION: although essential oils of Mentha piperita and Mentha pulegium had some effects on rumen microbial population but had no significant effects on performance and blood metabolites of Dallagh sheep.

Analysis of the rumen bacterial diversity of goats during shift from forage to concentrate diet

High-grain feeding used in the animal production is known to affect the host rumen bacterial community, but our understanding of consequent changes in goats is limited. This study was therefore aimed to evaluate bacterial population dynamics during 20 days adaptation of 4 ruminally cannulated goats to the high-grain diet (grain: hay – ratio of 40:60). The dietary transition of goats from the forage to the high-grain-diet resulted in the significant decrease of rumen fluid pH, which was however still higher than value established for acute or subacute ruminal acidosis was not diagnosed in studied animals. DGGE analysis demonstrated distinct ruminal microbial populations in hay-fed and grain-fed animals, but the substantial animal-to-animal variation were detected. Quantitative PCR showed for grain-fed animals significantly higher number of bacteria belonging to Clostridium leptum group at 10 days after the incorporation of corn into the diet and significantly lower concentration of bacteria belonging to Actinobacteria phylum at the day 20 after dietary change. Taxonomic distribution analysed by NGS at day 20 revealed the similar prevalence of the phyla Firmicutes and Bacteroidetes in all goats, significantly higher presence of the unclassified genus of groups of Bacteroidales and Ruminococcaceae in grain-fed animals and significantly higher presence the genus Prevotella and Butyrivibrio in the forage-fed animals. The three different culture-independent methods used in this study show that high proportion of concentrate in goat diet does not induce any serious disturbance of their rumen ecosystem and indicate the good adaptive response of caprine ruminal bacteria to incorporation of corn into the diet.

The effects of feeding 3-nitrooxypropanol at two doses on milk production, rumen fermentation, plasma metabolites, nutrient digestibility, and methane emissions in lactating Holstein cows

The objective of this study was to determine the effects of feeding 3-nitrooxypropanol (NOP) in the total mixed ration of lactating Holstein cows on rumen fermentation, ruminal microbial population, enteric methane production, milk production, nutrient digestibility, and blood metabolites. Fifteen ruminally cannulated Holstein cows in mid to late lactation were used in a 3 × 3 Latin square design study with 28-day periods. Cows were fed a 60%-forage diet (dry matter basis) with 2500 (HIGH), 1250 (LOW) or 0 (CON) mg/day of NOP. After a 20-day diet adaptation period, dry matter intake (DMI) and milk yield were recorded daily. Rumen digesta and rumen fluid were collected on Days 21 and 28 and ruminal pH was determined on Days 23–28. Methane emissions were measured on Days 23–27 using the sulfur hexafluoride tracer gas technique. Faecal and blood samples were taken on Days 25–27. Feeding NOP at either dose did not affect DMI, milk production or bodyweight gain. Total concentration of volatile fatty acids in rumen fluid did not differ; however, there was a decrease in molar proportion of acetate and increase in molar proportion of propionate with feeding NOP in a dose-dependent manner. Microbial profile and ruminal pH were not affected by treatment. Apparent total-tract digestibility of DM (62.7% vs 58.4%; P &lt; 0.05) and neutral detergent fibre (38.0% vs 30.7%; P &lt; 0.05) were increased with the HIGH dose compared with CON. Feeding NOP reduced methane yield from 19.9 to 15.3 g/kg DMI for CON versus LOW (P &lt; 0.05) and from 19.9 to 12.6 for CON versus HIGH (P &lt; 0.05). Feeding NOP at 1250 or 2500 mg/day reduced methane yield and affected ruminal volatile fatty acid profile without compromising DMI or apparent total-tract nutrient digestibility.

Effects of the inclusion of flaxseed and quercetin in the diet of fattening lambs on ruminal microbiota,in vitrofermentation and biohydrogenation of fatty acids

SUMMARYThirty-two lambs (n = 8 per treatment) were fed a total mixed ration (TMR) formulated either with palm oil (CTRL; 34 g palm oil/kg TMR) or flaxseed (FS) (85 g FS/kg TMR) alone or enriched with quercetin (QCT, 34 g palm oil plus 2 g QCT/kg TMR; FS-QCT, 85 g FS plus 2 g QCT/kg TMR). The animals were slaughtered after being fed for at least 5 weeks with the experimental diets and samples of ruminal contents and ruminal liquid were collected for quantitative real-time polymerase chain reaction analyses of ruminal microbial species and fatty acid profile orin vitrofermentation, respectively. Results demonstrated thatButyrivibriovaccenic acid (VA) andButyrivibriostearic acid (SA) producing bacteria copy numbers were decreased when FS was added to the diet of fattening lambs, which seemed to be in agreement with numerically (but not significantly) lower values for gas production, methane production and butyric acid duringin vitroincubation. Ciliate protozoa were significantly enhanced by QCT, which was in accordance with numerically (but not significantly) higher values forin vitromethane production. Moreover, the modifications observed in ruminal microbial populations (Butyrivibrioand ciliate protozoa) when FS and QCT were included together (but not separately) in the diet of fattening lambs were probably related to a trend towards significantly higher values of rumenic acid (RA) in ruminal content. In conclusion, when FS and QCT were administered together in the diet of fattening lambs quantitative changes in the ruminal microbiota were observed, which might have promoted an increment of RA concentration in ruminal contents.

Rapid changes in key ruminal microbial populations during the induction of and recovery from diet-induced milk fat depression in dairy cows.

The ruminant provides a powerful model for understanding the temporal dynamics of gastrointestinal microbial communities. Diet-induced milk fat depression (MFD) in the dairy cow is caused by rumen-derived bioactive fatty acids, and is commonly attributed to the changes in the microbial population. The aim of the present study was to determine the changes occurring in nine ruminal bacterial taxa with well-characterised functions, and abundance of total fungi, ciliate protozoa and bacteria during the induction of and recovery from MFD. Interactions between treatment and time were observed for ten of the twelve populations. The total number of both fungi and ciliate protozoa decreased rapidly (days 4 and 8, respectively) by more than 90% during the induction period and increased during the recovery period. The abundance of Streptococcus bovis (amylolytic) peaked at 350% of control levels on day 4 of induction and rapidly decreased during the recovery period. The abundance of Prevotella bryantii (amylolytic) decreased by 66% from day 8 to 20 of the induction period and increased to the control levels on day 12 of the recovery period. The abundance of Megasphaera elsdenii and Selenomonas ruminantium (lactate-utilising bacteria) increased progressively until day 12 of induction (>170%) and decreased during the recovery period. The abundance of Fibrobacter succinogenes (fibrolytic) decreased by 97% on day 4 of induction and increased progressively to an equal extent during the recovery period, although smaller changes were observed for other fibrolytic bacteria. The abundance of the Butyrivibrio fibrisolvens/Pseudobutyrivibrio group decreased progressively during the induction period and increased during the recovery period, whereas the abundance of Butyrivibrio hungatei was not affected by treatment. Responsive taxa were modified rapidly, with the majority of changes occurring within 8 d and their time course was similar to the time course of the induction of MFD, demonstrating a strong correlation between changes in ruminal microbial populations and MFD.

Rumen fermentation pattern, lipid metabolism and the microbial community of sheep fed a high-concentrate diet supplemented with a mix of medicinal plants

The aim of this study was to determine the effects of a medicinal plant mixture (MP), sunflower oil (SO) and a combination of the medicinal plant mixture and sunflower oil (MPSO) on fermentation end products, the fatty acid composition of the rumen fluid, the ruminal microbial population as well as antioxidant status in the blood of sheep fed a high-concentrate diet. Four rumen-fistulated rams were randomly assigned according to a 4×4 Latin square design and fed a basal diet consisting of 720g DM/day meadow hay and 540g DM/day barley grain. The basal diet was supplemented with no additive (control), a medicinal plant mixture (MP, 10% replacement of meadow hay; 72g DM/day), sunflower oil (SO, 36g/day) and the combination (MPSO). Before the in vivo experiment, 24h ruminal incubations in vitro were performed (meadow hay/barley grain; 400/600, w/w; MP; 10% replacement of meadow hay; SO; 3.5% DM; MPSO). The in vitro experiment with MP and MPSO increased the in vitro dry matter digestibility (P<0.001) and decreased methane production (P=0.021), while the MPSO treatment increased the concentration of polyunsaturated fatty acids (PUFA; P<0.001). In sheep, the rumen characteristics were not affected by the treatments. No treatment effect on the rumen eubacterial population was detected by the 16S-polymerase chain reaction-denaturizing gradient gel electrophoresis method. The beneficial effects of MP and MPSO on PUFA concentration observed in vitro were not fully confirmed in vivo. However, these results could point to the promising effects of using a medicinal plant mixture in high-concentrate diets of ruminants without adverse effects on the fermentation characteristics and microbial ecosystem in sheep rumen.

Potential of tannin-rich plants for modulating ruminal microbes and ruminal fermentation in sheep.

The objective of this work was to study nutritional strategies for decreasing methane production by ruminants fed tropical diets, combining in vitro and in vivo methods. The in vitro approach was used to evaluate the dose effect of condensed tannins (CT) contained in leaves of Gliricidia sepium, Leucaena leucocephala, and Manihot esculenta (39, 75, and 92 g CT/kg DM, respectively) on methane production and ruminal fermentation characteristics. Tannin-rich plants (TRP) were incubated for 24 h alone or mixed with a natural grassland hay based on Dichanthium spp. (control plant), so that proportions of TRP were 0, 0.25, 0.5, 0.75, and 1.0. Methane production, VFA concentration, and fermented OM decreased with increased proportions of TRP. Numerical differences on methane production and VFA concentration among TRP sources may be due to differences in their CT content, with greater effects for L. leucocephala and M. esculenta than for G. sepium. Independently of TRP, the response to increasing doses of CT was linear for methane production but quadratic for VFA concentration. As a result, at moderate tannin dose, methane decreased more than VFA. The in vivo trial was conducted to investigate the effect of TRP on different ruminal microbial populations. To this end, 8 rumen-cannulated sheep from 2 breeds (Texel and Blackbelly) were used in two 4 × 4 Latin square designs. Diets were fed ad libitum and were composed of the same feeds used for the in vitro trial: control plant alone or combined with pellets made from TRP leaves at 44% of the diet DM. Compared to TRP, concentration of Ruminococcus flavefaciens was greater for the control diet and concentration of Ruminococcus albus was least for the control diet. The methanogen population was greater for Texel than for Blackbelly. By contrast, TRP-containing diets did not affect protozoa or Fibrobacter succinogenes numbers. Hence, TRP showed potential for mitigating methane production by ruminants. These findings suggest that TRP fed as pellets could be used to decrease methane production.

Effects of supplementation of Simmental steers with 2-methylbutyrate on rumen microflora, enzyme activities and methane production

The objective of this study was to evaluate the effects of 2-methylbutyrate supplementation on rumen microflora, enzyme activities and methane production in Simmental steers consuming a diet consisting of 600g/kg corn stover and 400g/kg concentrate (dry matter [DM] basis). Eight ruminally cannulated Simmental steers were used in a replicated 4×4 Latin square design. The treatments were: control (without 2-methylbutyrate), low 2-methylbutyrate (LMB), medium 2-methylbutyrate (MMB) and high 2-methylbutyrate (HMB) with 0, 8.4, 16.8 and 25.2g 2-methylbutyrate per steer and per day, respectively. Dry matter intake (averaged 9kg/day) was restricted to a maximum of 0.9 of ad libitum intake. Whether direct counts, roll-tube technique or real-time PCR quantification were used, populations of total bacteria, cellulolytic bacteria and anaerobic fungi linearly increased (P<0.04) and were higher (P<0.05) for MMB and HMB than for control and LMB, whereas those of protozoa and total methanogens linearly reduced and were lower for MMB and HMB than for control and LMB. With increasing 2-methylbutyrate supplementation, real-time PCR quantification of populations of Ruminococcus albus, Ruminococcus flavefaciens, Bufyrivibrio fibrisolvens and Fibrobacter succinogenes linearly increased (P<0.05) and was higher for MMB and HMB than for control (P<0.05). Activities of CMCase, xylanase and β-glucosidase linearly increased (P<0.05) and were higher (P<0.05) for MMB and HMB than for control and LMB, whereas that of protease linearly reduced (P<0.05) and was lower for MMB and HMB than for control and LMB (P<0.05). Activities of α-amylase and α-glucosidase tended to be higher (P<0.08) for MMB and HMB than for control and LMB, but activity of urease tended to be lower for MMB and HMB than for control and LMB. Methane production linearly decreased (P<0.01) and was lower for MMB and HMB than for control (P<0.05) with increasing 2-methylbutyrate supplementation. Effective degradabilities of cellulose and hemicellulose of corn stover linearly increased (P<0.01) and were higher for MMB and HMB than for control (P<0.05), whereas that of crude protein in concentrate linearly decreased (P<0.01) and was lower for MMB and HMB than for control and LMB (P<0.05) with increasing 2-methylbutyrate supplementation. The present results indicate that supplementation of diet with 2-methylbutyrate altered ruminal microbial populations and improved ruminal enzyme activities in a dose-dependent manner in steers fed high-roughage diet. In the experimental conditions of this trial, the optimum daily dose of 2-methylbutyrate at 16.8g per steer is suggested.

Effect of banana flower powder supplementation as a rumen buffer on rumen fermentation efficiency and nutrient digestibility in dairy steers fed a high-concentrate diet

Four rumen-fistulated dairy steers, two and a half year old with liveweight of 220±15.0kg, were randomly assigned according to a 4×4 Latin square design to study the effect of banana flower powder (BAFLOP) supplementation as a rumen buffering agent on ruminal pH, nutrient digestibility and rumen fermentation fed a high-concentrate diet. The four dietary treatments were BAFLOP supplementation at 0, 10, 20 and 30g/kg of dry matter intake (DMI), respectively. During the experimental periods, all steers were fed a diet containing roughage to concentrate ratio of 30:70 at 20g DMI/kg of body weight and rice straw was used as a roughage source. Based on the present study, the results revealed that dry matter, organic matter and crude protein digestibilities were not affected (P>0.05) by BAFLOP supplementation, whereas digestibilities of neutral detergent fiber and acid detergent fiber increased with the increasing levels of BAFLOP supplementation (P<0.05). It was also found that total nitrogen (N) intakes were similar among treatments. However, fecal N excretions decreased with the increasing levels of BAFLOP supplementation, while urinary N excretions were similar among treatments. BAFLOP supplementation increased N balance both absorption and retention (P<0.05). Moreover, purine derivative absorption and microbial protein synthesis were increased by BAFLOP supplementation, whereas efficiency of microbial nitrogen supply (EMNS) and microbial nitrogen supply were similar among treatments. In addition, ruminal temperature, ammonia nitrogen, and blood urea nitrogen were not influenced by BAFLOP supplementation, whilst ruminal pH enhanced (P<0.05) in steers supplemented with BAFLOP at 20 and 30g/kg of DMI. The concentration of total volatile fatty acid and acetic acid increased with BAFLOP supplementation, whereas propionic and butyric acid remained the same. The present findings showed that BAFLOP supplementation enhanced total bacterial, protozoal, and cellulolytic bacterial growth, while numbers of fungal zoospores, amylolytic and proteolytic bacteria were similar among treatments. In conclusion, BAFLOP supplementation improved rumen ecology and nutrient digestibility by enhancing ruminal pH, nitrogen utilization, EMNS and ruminal microbial population. This study suggested that BAFLOP could be supplemented as a rumen buffering agent at 20–30g/kg of DMI.

Effective reduction of enteric methane production by a combination of nitrate and saponin without adverse effect on feed degradability, fermentation, or bacterial and archaeal communities of the rumen

This study evaluated the effects of Quillaja saponin (0.6 and 1.2g/L), propynoate (4 and 8mM), and nitrate (5 and 10mM), alone or in combinations, on methanogenesis, fermentation, bacterial and archaeal communities, and abundances of select ruminal microbial populations. All treatment decreased methane production, but combination of all three inhibitors at high dose achieved the greatest inhibition (85%). Propynoate, alone or in combination with nitrate or saponin, decreased feed degradability and total volatile fatty acid (TVFA) concentrations. However, saponin and nitrate alone at high dose and in combination at low dose inhibited methanogenesis substantially while increasing feed degradability and TVFA concentrations. The abundances of methanogens were lowered by all inhibitors except saponin alone. Fibrobacter succinogenes and Ruminococcus flavefaciens were increased by saponin, both alone and in combination with nitrate, but inhibited by propynoate. Combination of saponin and nitrate may have practical application in mitigating methane emission from ruminants.

Board-invited review: Rumen microbiology: Leading the way in microbial ecology1,2

Robert Hungate, considered the father of rumen microbiology, was the first to initiate a systematic exploration of the microbial ecosystem of the rumen, but he was not alone. The techniques he developed to isolate and identify cellulose-digesting bacteria from the rumen have had a major impact not only in delineating the complex ecosystem of the rumen but also in clinical microbiology and in the exploration of a number of other anaerobic ecosystems, including the human hindgut. Rumen microbiology has pioneered our understanding of much of microbial ecology and has broadened our knowledge of ecology in general, as well as improved the ability to feed ruminants more efficiently. The discovery of anaerobic fungi as a component of the ruminal flora disproved the central dogma in microbiology that all fungi are aerobic organisms. Further novel interactions between bacterial species such as nutrient cross feeding and interspecies H2 transfer were first described in ruminal microorganisms. The complexity and diversity present in the rumen make it an ideal testing ground for microbial theories (e.g., the effects of nutrient limitation and excess) and techniques (such as 16S rRNA), which have rewarded the investigators that have used this easily accessed ecosystem to understand larger truths. Our understanding of characteristics of the ruminal microbial population has opened new avenues of microbial ecology, such as the existence of hyperammonia-producing bacteria and how they can be used to improve N efficiency in ruminants. In this review, we examine some of the contributions to science that were first made in the rumen, which have not been recognized in a broader sense.

Milk odd- and branched-chain fatty acids as biomarkers of rumen function—An update

The main odd- and branched-chain fatty acids (OBCFA) in milk of dairy cows are isomers of tridecanoic acid (iso C13:0), tetradecanoic acid (iso C14:0), pentadecanoic acid (C15:0, iso C15:0 and anteiso C15:0), hexadecanoic acid (iso C16:0) and heptadecanoic acid (C17:0, iso C17:0 and anteiso C17:0). OBCFA are suggested to reflect rumen function (e.g. ruminal fermentation pattern, including methane, duodenal flow of microbial protein and acidosis). This relies on their predominant origin, i.e. bacteria leaving the rumen. The OBCFA are synthesized de novo by ruminal bacteria and incorporated in their cell membrane, suggesting a direct relation with bacterial biomass. Their potential as duodenal markers to quantify bacterial protein is strengthened by their constant relation with bacterial N content over a diversity of bacterial groups. From a limited database, evidence was shown of a useful relation of milk OBCFA yield with microbial protein flow from the rumen, but more research is needed to elucidate some discrepancies under diverse dietary regimes.Further, variation in the OBCFA profile of pure strains of ruminal bacteria were reported and are, in the current review, linked with their production of metabolites. From this, it can be assumed that the rumen fermentation pattern is related to the rumen OBCFA profile, which seems consistent for milk OBCFA. The close stoichiometric relation between ruminal VFA and methane further opens perspective for the use of OBCFA profiles in milk to quantify methane emissions. OBCFA consistently contributing to the predictive models, irrespective of the modeling approach are: iso C14:0 and iso C15:0, which positively relate to acetate and methane and negatively to propionate; and C15:0 and C17:0 which show an inverse relationship. Anteiso C15:0 seemed only relevant in the prediction of butyrate proportions.As changes in the ruminal microbial population (e.g. increased dominance of Streptococcus bovis) sometimes initiate a chain of events that eventually might lead to (sub-acute) ruminal acidosis, OBCFA in milk fat are targeted as candidates for the early detection of ruminal acidosis. Increasing C17:0+C17:1 cis-9 and decreasing iso C14:0 concentration show potential as indicators of sub-acute acidosis or were obvious before clinical symptoms of acute acidosis occurred. Collection of more experimental data is currently on-going for the development of more robust models to classify rumen health in continuous probability classes rather than discrete acidotic vs. non-acidotic cases.

Effects of inactivated and live cells of Saccharomyces cerevisiae on in vitro ruminal fermentation of diets with different forage:concentrate ratio

SUMMARYThe effects of yeast Saccharomyces cerevisiae, either inactivated (by osmotic pressure, designated IY) or provided as a culture containing live yeast cells (YC), on ruminal fermentation of two different diets were investigated in vitro. Total mixed rations (TMR) having forage:concentrate ratios of 0·6:0·4 (medium–high forage diet) and 0·2:0·8 (low-forage diet) were incubated in batch cultures of mixed ruminal micro-organisms to which either IY (to reach concentrations of 500 and 250 mg product/l incubation medium) or YC (at a concentration of 150 mg product/l) were added directly as powder. To evaluate the effects of the additive on ruminal microbial population, sheep used as donors of rumen fluid were allocated to three experimental groups: Control (no additive), IY and YC, that received a diet with the corresponding additive for 10 days. With both diets, YC decreased ruminal pH compared to control, whereas IY had no effect. Adding yeast products to the high-fibre diet affected total volatile fatty acid (VFA) production and VFA composition, in general with a slight increase in IY and a significantly greater increase in response to the addition of YC. Ammonia nitrogen (P=0·006), total gas production (P&lt;0·001) and in vitro dry matter disappearance (IVD) (P&lt;0·001) showed the highest values with YC. Methane production was higher than the control when the IY inoculum was used, and increased even more with the YC inoculum (P&lt;0·001). With the high-concentrate TMR, no effects on total VFA concentration were observed when yeast additives were used. Similar trends were shown for lactate and methane production and total gas production, where values tended to be higher when using the YC inoculum (P values of 0·055, &lt;0·001, 0·006 and &lt;0·001, respectively). After 144 h of incubation, differences were observed only with the high-fibre diet in the cumulative gas production at 24 h of incubation and in the average fermentation rate, which was greater with YC, although the asymptotic gas production was not affected. These results indicate that live yeasts affect ruminal fermentation slightly more than inactivated yeasts, although both products require a regular administration and some adaptation of the ruminal microbial population for the stimulatory effects to become apparent. The effects of yeasts on ruminal fermentation are diet-dependent, being more noticeable with a high-fibre substrate, and subtle with a high-concentrate diet.

Effect of ruminal pulse dose of polyunsaturated fatty acids on ruminal microbial populations and duodenal flow and milk profiles of fatty acids

The objective of this study was to examine the effect of ruminal pulse dose of free linoleic acid (LA) and free docosahexaenoic acid (DHA) on microbial populations in the rumen, duodenal fatty acid (FA) flow, milk composition, and milk FA profiles of Chinese Holstein dairy cows. Four rumen- and duodenal-fistulated Chinese Holstein cows in mid lactation (138.5±10d in milk) were randomly assigned to 3 treatment groups and 1 control group in a 4×4 Latin square design over 4 periods (3 wk per period). Diets contained either no LA or 2.7% LA and either no DHA or 0.5% DHA in a 2×2 factorial arrangement of treatments. Ruminal pulse dose with DHA increased counts of Megasphaera elsdenii, decreased Fibrobacter succinogenes, but did not affect Butyrivibrio fibrisolvens or Ruminococcus flavefaciens. The pulse dose of LA at 2.7% dry matter had no effect on the population sizes of the 3 major cellulolytic bacterial species or M. elsdenii, and no interaction was observed between LA and DHA. The pulse dose of LA or DHA, either alone or in combination, increased the duodenal flow of vaccenic acid (VA). The milk VA and cis-9,trans-11 conjugated linoleic acid (CLA) contents also increased in response to the fatty acid pulse dose, and the pulse dose of both LA and DHA together had the most profound stimulatory effect. This study indicated that ruminal pulse dose of LA or DHA could be used to increase duodenal flow of VA and the milk contents of potentially health-promoting FA, such as VA and cis-9,trans-11 CLA. These results might be useful in formulating dietary interventions to improve milk cis-9,trans-11 CLA contents.

Associative effects of supplementing rice straw‐based diet with cornstarch on intake, digestion, rumen microbes and growth performance of Huzhou lambs

Thirty-six male Hu lambs consuming a rice straw-based diet were used in a 60-day trial to study the associative effects of cornstarch supplementation on intake, digestion, ruminal microbial population and growth performance. All animals were fed rice straw ad libitum together with 160 g/day of rapeseed meal and supplemented with cornstarch at levels of 0 (control), 60, 120 or 180 g/day, respectively. Increment of supplementary cornstarch showed little influence on rice straw intake. Optimal growth performance and highest apparent digestibility of organic matter was achieved in the 120 g/day cornstarch group (P < 0.05), while the digestibilities of neutral detergent fiber and crude protein were significantly decreased by 180 g/day cornstarch (P < 0.05). Similar results were observed for carboxymethyl cellulose activity and relative populations of cellulolytic bacteria (Ruminococcus albus, Ruminococcus flavefaciens and Fibrobacter succinogene). Blood urea nitrogen was reduced by supplementary cornstarch, indicating enhanced protein utilization efficiency. Carcass traits were all significantly improved by supplementary cornstarch. These results suggested that proper amounts of starch supplementation (within 0.5% BW) has little adverse effect on forage utilization, but could effectively improve growth performance. High levels of cornstarch, however, would decrease cellulase activity and populations of cellulolytic bacteria, and hence the digestibility of forage.