The objective of the current study was to evaluate 30 previously uncharacterized pure plant secondary metabolites (PSM) for effects on in vitro gas production (GP) and methane concentration. Purified compounds (n = 4) were incubated in buffered rumen fluid for 48 h at a rate of 25 mg per g substrate. Gas production was measured using ANKOM RF pressure analysers and gas composition was measured using gas chromatography. Dry matter and fibre digestibility and volatile fatty acid (VFA) concentrations were determined. Data were analysed using a linear mixed model with fixed effect of treatment, random effect of experimental run and blank as a covariate and Dunnett’s test to compare each treatment to a control. Sabenine, apigenin, galangin, isoliquirtigenin, quercetin, rutin, vitexin, abscisic acid, and uridine reduced methane concentration, with a tendency for reduction by kaempherol. Sabenine, thymol, apigenin, quercetin, rutin, vitexin, abscisic acid, and uridine reduced methane production, with the greatest reduction occurring for rutin (81.8%), vitexin (81.7%), and thymol (80.5%). Eight compounds increased methane production compared to control, with stigmasterol having the greatest increase (173.0%). Out of the compounds that reduced methane emissions, a reduction in fibre digestibility was observed for all except quercetin and thymol. Minimal effects of PSM on VFA profile were observed, with myrtenal increasing proportion of acetate, alpha-humulene, alpha-longipinene and beta-caryophyllene increasing proportion of propionate, and thymol, apigenin, hyperoside, and verbenone increasing proportion of butyrate. Results suggest that quercetin and thymol warrant further exploration as potential feed additives to reduce methane emissions.

This study evaluated the effects of dietary yeast culture (YC) supplementation on rumen microbiota and lactation performance in dairy goats. Twenty mid-lactation dairy goats were selected and divided into two groups: the control (CON) group was fed a basal diet; the YC group was supplemented with 10 g of YC in 1 kg of basal diet. The administration of YC was associated with a significant increase in dry matter intake, milk yield, milk protein yield, and milk lactose yield in dairy goats (P < 0.05). Additionally, serum total protein, albumin, creatinine, glucose, superoxide dismutase, and catalase levels were increased (P < 0.05). Furthermore, there was an increase in rumen pH and NH3-N levels (P < 0.05), while volatile fatty acid levels were observed to decrease (P < 0.05). The study found no significant difference in the α-diversity of bacteria and fungi between the YC and CON groups (P > 0.05). However, 15 bacterial genera and 13 fungal genera were upregulated (P < 0.05), while 4 bacterial genera and 11 fungal genera were downregulated (P < 0.05) in the YC group. The relative abundance of pathogenic fungi Dipodascus and Gibberella decreased (P < 0.05). Correlation analysis revealed that the bacterial genera were not significantly correlated with lactation performance (P > 0.05), whereas fungal genera Dipodascus and Gibberella were significantly (P < 0.05) correlated with lactation performance. In conclusion, the study demonstrated that YC can influence the rumen microbial composition, reduce the abundance of harmful fungi in the rumen, and improve lactation performance in dairy goats, suggesting that the addition of YC to dairy goat diets has good application prospects.

This observational study aimed to describe the diurnal pattern of reticuloruminal contraction rate (RRCR) and the proportion of time spent ruminating by cattle, using two commercial devices equipped with triaxial accelerometers: an indwelling bolus (placed in the reticulum) and a neck collar. The three objectives of this study were firstly to determine whether the indwelling bolus provided observations consistent with RRCR as determined by clinical examination using auscultation and ultrasound, secondly to compare estimates of time spent ruminating using the indwelling bolus and a collar-based accelerometer, and finally to describe the diurnal pattern of RRCR using the indwelling bolus data. Six rumen-fistulated, non-lactating Jersey cows were fitted with an indwelling bolus (SmaXtec Animal Care GmbH, Graz, Austria) and a neck collar (Silent Herdsman, Afimilk Ltd. Kibbutz Afikim, Israel), and data were collected over two weeks. Cattle were housed together in a single straw-bedded pen and fed ad libitum hay. To assess the agreement between the indwelling bolus and traditional methods of assessing reticuloruminal contractility in the first week, the RRCR was determined over 10 min, twice a day, by ultrasound and auscultation. Mean inter-contraction intervals (ICI) derived from bolus and ultrasound, and from auscultation were 40.4 ± 4.7, 40.1 ± 4.0 and 38.4 ± 3.3 s. Bland–Altmann plots showed similar performance of the methods with small biases. The Pearson correlation coefficient for the time spent ruminating derived from neck collars and indwelling boluses was 0.72 (highly significant, P < 0.001). The indwelling boluses generated a consistent diurnal pattern for all the cows. In conclusion, a robust relationship was observed between clinical observation and the indwelling boluses for estimation of ICI and, similarly, between the indwelling bolus and neck collar for estimating rumination time. The indwelling boluses showed a clear diurnal pattern for RRCR and time spent ruminating, indicating that they should be useful for assessing reticuloruminal motility.

The experiment reported in this research paper aimed to evaluate the effects of high-starch or starch and oil-supplemented diets on rumen and faecal bacteria, and explore links between the structure of bacterial communities and milk fatty acid (FA) profiles. We used four Holstein dairy cows in a 4 × 4 Latin square design. Cows were fed a diet rich in cereals (high-starch diet with 23% starch content on dry matter (DM) basis), a diet supplemented with saturated FA from Ca salts of palm oil + 18% DM starch, a diet with high content of monounsaturated FA (from extruded rapeseeds) + 18% DM starch or a diet rich in polyunsaturated FA (from extruded sunflower seeds) + 17% DM starch. At the end of each experimental period, cows were sampled for rumen and faecal contents, which were used for DNA extraction and amplicon sequencing. Partial least squares (PLS) regression analysis highlighted diet-related changes in both rumen and faecal bacterial structures. Sparse PLS discriminant analysis was further employed to identify biologically relevant operational taxonomical units (OTUs) driving these differences. Our results show that Butyrivibrio discriminated the high-starch diet and linked positively with higher concentrations of milk odd- and branched-chain FA. YS2-related OTUs were key taxa distinguishing diets supplemented with Ca salts of palm oil or sunflower seeds and correlated positively with linoleic acid in milk. Similarly, diets modulated faecal bacterial composition. However, correlations between changes in faecal and rumen bacteria were poor. With this work, we demonstrated that high-starch or lipid-supplemented diets affect rumen and faecal bacterial community structure, and these changes could have a knock-on effect on milk FA profiles.

We review key findings of one the most cited papers in the 75-year history of BJN. We then identify important consequent developments, as well as opportunities to use analytical and molecular biology advances to maximise conversion of non-protein nitrogen into microbial protein.

The supplementation of ruminant diets with exogenous cellulolytic enzymes can improve their digestibility and feeding value. The objective of this study was to determine the effect of supplementing roughage (rice straw) and concentrate with inoculants containing four fungal strains (Pleurotus ostreatus, Phanerochaete chrysosporium, Trichoderma reesei and Trichoderma viride) and four bacterial strains (Paenibacillus polymyxa, Bacillus megaterium, Bacillus circulans and Bacillus subtilis), given separately or as a mixture, as a source of exogenous cellulolytic enzymes, on basic rumen parameters in vitro, including digestibility and methane production. A batch culture trial was used to select the best supplements, and a long-term rumen simulation technique (RUSITEC) was used to evaluate the effects of P. chrysosporium, B. subtilis, and a 1 : 1 mixture of these two on dietary component digestibility and fermentation parameters. In the batch culture evaluation, there were significant increases in the organic matter (OM) digestibility, the total gas production expressed as ml/g of dry matter, the OM, the neutral detergent fibre (NDF) and the acid detergent fibre (ADF) of the supplemented rations, as compared to the control, excluding the rations supplemented with T. viride and B. circulans. In the RUSITEC, the ration supplemented with mixed inoculants showed significantly higher digestibility of crude protein, ether extract, NDF and ADF than did the ration supplemented with the P. chrysosporium and B. subtilis inoculants. It can be concluded that the simultaneous use of fungal and bacterial exogenous cellulases on rice straw roughage improves its digestibility, without negative effects on other rumen parameters.

The relationship between DM intake (DMI) and enteric methane emission is well established in ruminant animals but may depend on measurement technique (e.g. spot v. continuous gas sampling) and rumen environment (e.g. use of fermentation modifiers). A previous meta-analysis has shown a poor overall (i.e. 24 h) relationship of DMI with enteric methane emission in lactating dairy cows when measured using the GreenFeed system (GF; Symposium review: uncertainties in enteric methane inventories, measurement techniques, and prediction models. Journal of Dairy Science 101, 6655 to 6674). Therefore, we examined this relationship in a 15-week experiment with lactating dairy cows receiving a control diet or a diet containing the investigational product 3-nitrooxypropanol (3-NOP), an enteric methane inhibitor, applied at 60 mg/kg feed DM. Daily methane emission, measured using GF, and DMI were clustered into 12 feed-intake timeslots of 2 h each. Methane emission and DMI were the lowest 2 h before feeding and the highest within 6 h after feed provision. The overall (24 h) relationship between methane emission and DMI was poor (R2 = 0.01). The relationship for the control (but not 3-NOP) cows was improved (R2 = 0.31; P < 0.001) when DMI was allocated to timeslots and was strongest (R2 = 0.51; P < 0.001) 8 to 10 h after feed provision. Analysis of the 3-NOP emission data showed marked differences in the mitigation effect over time. There was a lack of effect in the 2-h timeslot before feeding, the mitigation effect was highest (45%) immediately after feed provision, persisted at around 32% to 39% within 10 h after feed provision, and decreased to 13%, 4 h before feeding. These trends were clearly related to DMI (i.e. 3-NOP intake) by the cows. The current analysis showed that the relationship of enteric methane emission, as measured using GF, and DMI in dairy cows depends on the time of measurement relative to time of feeding. The implication of this finding is that a sufficient number of observations, covering the entire 24-h feeding cycle, have to be collected to have representative emission estimates using the GF system. This analysis also revealed that the methane mitigation effect of 3-NOP is highest immediately after feed provision and lowest before feeding.

Many studies have shown that metabolic efficiency of ruminants can be significantly decreased when B-vitamin supply is insufficient. Under the present state of knowledge, the amounts of B vitamins available for intestinal absorption cannot be predicted based on diet composition. Therefore, in an attempt to increase our understanding of the effects of dietary factors, on B-vitamin supply for dairy cows, the effects of increasing amounts of extruded linseed in diets based on hay (permanent grassland hay, H; Experiment 1) or corn silage (CS; Experiment 2) on apparent ruminal synthesis (ARS) of thiamin, riboflavin, niacin, vitamin B6, folates and vitamin B12 were evaluated. In each experiment, four lactating Holstein cows fitted with cannulas in the rumen and the proximal duodenum were used in a 4 × 4 Latin square design. In both experiments, the dietary treatments consisted of an increasing supply of extruded linseed representing 0%, 5%, 10% or 15% of diet DM. The forage : concentrate ratios were 50 : 50 and 60 : 40 for Experiments 1 and 2, respectively. Duodenal flow was determined using YbCl3 as a marker. The ARS of each B vitamin was calculated as duodenal flow – daily intake. In both experiments, treatments did not affect thiamin, riboflavin, niacin and vitamin B12 duodenal flow or ARS. Increasing the dietary concentration of extruded linseed decreased folate intake in Experiment 1 and vitamin B6 intake in Experiment 2 but resulted in a greater duodenal flow of vitamin B6 and folates regardless of the forage used in basal diet. Greater dietary linseed concentrations decreased vitamin B6 apparent degradation in the rumen in CS-based diet only and increased folate ARS in both H- and CS-based diets. Increasing linseed concentration of isonitrogenous and isoenergetic diets increased vitamin B6 and folate supply to dairy cows, both with H- and CS-based diets.

The ruminal degradation of P bound in phytate (InsP6) can vary between feeds, but data on ruminal degradation of InsP6 from different feedstuffs for cattle are rare. One objective of this study was to increase the data base on ruminal effective degradation of InsP6 (InsP6ED) and to assess if InsP6ED of compound feeds (CF) can be calculated from comprising single feeds. As a second objective, use of near-infrared spectroscopy (NIRS) to predict InsP6 concentrations was tested. Nine single feeds (maize, wheat, barley, faba beans, soybeans, soybean meal (SBM), rapeseed meal (RSM), sunflower meal (SFM), dried distillers’ grains with solubles (DDGS)) and two CF (CF1/CF2), consisting of different amounts of the examined single feeds, were incubated for 2, 4, 8, 16, 24, 48 and 72 h in the rumen of three ruminally fistulated Jersey cows. Samples of CF were examined before (CF1/CF2 Mash) and after pelleting (CF1/CF2 Pellet), and InsP6ED was calculated for all feeds at two passage rates (InsP6ED5: k = 5%/h; InsP6ED8: k = 8%/h). For CF1 and CF2, InsP6ED was also calculated from values of the respective single feeds. Near-infrared spectra were recorded in duplicate and used to establish calibrations to predict InsP6 concentration. Besides a global calibration, also local calibrations were evaluated by separating samples into different data sets based on their origin. The InsP6ED8 was highest for faba beans (91%), followed by maize (90%), DDGS (89%), soybeans (85%), wheat (76%) and barley (74%). Lower values were determined for oilseed meals (48% RSM, 65% SFM, 66% SBM). Calculating InsP6ED of CF from values of single feeds underestimated observed values up to 11 percentage points. The NIRS calibrations in general showed a good performance, but statistical key data suggest that local calibrations should be established. The wide variation of InsP6ED between feeds indicates that the ruminal availability of P bound in InsP6 should be evaluated individually for feeds. This requires further in situ studies with high amounts of samples for InsP6 analysis. Near-infrared spectroscopy has the potential to simplify the analytical step of InsP6 in the future, but the calibrations need to be expanded.

The rumen contains a great diversity of prokaryotic and eukaryotic microorganisms that allow the ruminant to utilize ligno-cellulose material and to convert non-protein nitrogen into microbial protein to obtain energy and amino acids. However, rumen fermentation also has potential deleterious consequences associated with the emissions of greenhouse gases, excessive nitrogen excreted in manure and may also adversely influence the nutritional value of ruminant products. While several strategies for optimizing the energy and nitrogen use by ruminants have been suggested, a better understanding of the key microorganisms involved and their activities is essential to manipulate rumen processes successfully. Diet is the most obvious factor influencing the rumen microbiome and fermentation. Among dietary interventions, the ban of antimicrobial growth promoters in animal production systems has led to an increasing interest in the use of plant extracts to manipulate the rumen. Plant extracts (e.g. saponins, polyphenol compounds, essential oils) have shown potential to decrease methane emissions and improve the efficiency of nitrogen utilization; however, there are limitations such as inconsistency, transient and adverse effects for their use as feed additives for ruminants. It has been proved that the host animal may also influence the rumen microbial population both as a heritable trait and through the effect of early-life nutrition on microbial population structure and function in adult ruminants. Recent developments have allowed phylogenetic information to be upscaled to metabolic information; however, research effort on cultivation of microorganisms for an in-depth study and characterization is needed. The introduction and integration of metagenomic, transcriptomic, proteomic and metabolomic techniques is offering the greatest potential of reaching a truly systems-level understanding of the rumen; studies have been focused on the prokaryotic population and a broader approach needs to be considered.

All livestock animal species harbour complex microbial communities throughout their digestive tract that support vital biochemical processes, thus sustaining health and productivity. In part as a consequence of the strong and ancient alliance between the host and its associated microbes, the gut microbiota is also closely related to productivity traits such as feed efficiency. This phenomenon can help researchers and producers develop new and more effective microbiome-based interventions using probiotics, also known as direct-fed microbials (DFMs), in Animal Science. Here, we focus on one type of such beneficial microorganisms, the yeast Saccharomyces. Saccharomyces is one of the most widely used microorganisms as a DFM in livestock operations. Numerous studies have investigated the effects of dietary supplementation with different species, strains and doses of Saccharomyces (mostly Saccharomyces cerevisiae) on gut microbial ecology, health, nutrition and productivity traits of several livestock species. However, the possible existence of Saccharomyces which are indigenous to the animals’ digestive tract has received little attention and has never been the subject of a review. We for the first time provide a comprehensive review, with the objective of shedding light into the possible existence of indigenous Saccharomyces of the digestive tract of livestock. Saccharomyces cerevisiae is a nomadic yeast able to survive in a broad range of environments including soil, grass and silages. Therefore, it is very likely that cattle and other animals have been in direct contact with this and other types of Saccharomyces throughout their entire existence. However, to date, the majority of animal scientists seem to agree that the presence of Saccharomyces in any section of the gut only reflects dietary contamination; in other words, these are foreign organisms that are only transiently present in the gut. Importantly, this belief (i.e. that Saccharomyces come solely from the diet) is often not well grounded and does not necessarily hold for all the many other groups of microbes in the gut. In addition to summarizing the current body of literature involving Saccharomyces in the digestive tract, we discuss whether the beneficial effects associated with the consumption of Saccharomyces may be related to its foreign origin, though this concept may not necessarily satisfy the theories that have been proposed to explain probiotic efficacy in vivo. This novel review may prove useful for biomedical scientists and others wishing to improve health and productivity using Saccharomyces and other beneficial microorganisms.

Eight ruminally-fistulated wethers were used to examine the temporal effects of afternoon (PM; 1600h) v. morning (AM; 0800 h) allocation of fresh spring herbage from a perennial ryegrass (Lolium perenne L.)-based pasture on fermentation and microbial community dynamics. Herbage chemical composition was minimally affected by time of allocation, but daily mean ammonia concentrations were greater for the PM group. The 24-h pattern of ruminal fermentation (i.e. time of sampling relative to time of allocation), however, varied considerably for all fermentation variables (P⩽0.001). Most notably amongst ruminal fermentation characteristics, ammonia concentrations showed a substantial temporal variation; concentrations of ammonia were 1.7-, 2.0- and 2.2-fold greater in rumens of PM wethers at 4, 6 and 8h after allocation, respectively, compared with AM wethers. The relative abundances of archaeal and ciliate protozoal taxa were similar across allocation groups. In contrast, the relative abundances of members of the rumen bacterial community, like Prevotella 1 (P=0.04), Bacteroidales RF16 group (P=0.005) and Fibrobacter spp. (P=0.008) were greater for the AM group, whereas the relative abundance of Kandleria spp. was greater (P=0.04) for the PM group. Of these taxa, only Prevotella 1 (P=0.04) and Kandleria (P<0.001) showed a significant interaction between time of allocation and time of sampling relative to feed allocation. Relative abundances of Prevotella 1 were greater at 2h (P=0.05), 4h (P=0.003) and 6h (P=0.01) after AM allocation of new herbage, whereas relative abundances of Kandleria were greater at 2h (P=0.003) and 4h (P<0.001) after PM allocation. The early post-allocation rise in ammonia concentrations in PM rumens occurred simultaneously with sharp increases in the relative abundance of Kandleria spp. and with a decline in the relative abundance of Prevotella. All measures of fermentation and most microbial community composition data showed highly dynamic changes in concentrations and genus abundances, respectively, with substantial temporal changes occurring within the first 8h of allocating a new strip of herbage. The dynamic changes in the relative abundances of certain bacterial groups, in synchrony with a substantial diurnal variation in ammonia concentrations, has potential effects on the efficiency by which N is utilised by the grazing ruminant.

Feeding ruminants a high-grain (HG) diet is a widely used strategy to improve milk yield and cost efficiency. However, it may cause certain metabolic disorders. At present, information about the effects of HG diets on the systemic metabolic profile of goats and the correlation of such diets with rumen bacteria is limited. In the present study, goats were randomly divided into two groups: one was fed the hay diet (hay; n = 5), while the other was fed HG diets (HG; n = 5). On day 50, samples of rumen contents, peripheral blood serum and liver tissues were collected to determine the metabolic profiles in the rumen fluid, liver and serum and the microbial composition in rumen. The results revealed that HG diets reduced (P < 0.05) the community richness and diversity of rumen microbiota, with an increase in the Chao 1 and Shannon index and a decrease in the Simpson index. HG diets also altered the composition of rumen microbiota, with 30 genera affected (P < 0.05). Data on the metabolome showed that the metabolites in the rumen fluid, liver and serum were affected (variable importance projection > 1, P <0.05) by dietary treatment, with 47, 10 and 27 metabolites identified as differentially metabolites. Pathway analysis showed that the common metabolites in the shared key pathway (aminoacyl-transfer RNA biosynthesis) in the rumen fluid, liver and serum were glycine, lysine and valine. These findings suggested that HG diets changed the composition of the rumen microbiota and metabolites in the rumen fluid, liver and serum, mainly involved in amino acid metabolism. Our findings provide new insights into the understanding of diet-related systemic metabolism and the effects of HG diets on the overall health of goats.

Understanding the rumen microbial ecosystem requires the identification of factors that influence the community structure, such as nutrition, physiological condition of the host and host–microbiome interactions. The objective of the current study was to describe the rumen microbial communities before, during and after a complete rumen content transfer. The rumen contents of one donor cow were removed completely and used as inoculum for the emptied rumen of the donor itself and three acceptor cows under identical physiological and nutritional conditions. Temporal changes in microbiome composition and rumen function were analysed for each of four cows over a period of 6 weeks. Shortly after transfer, the cows showed different responses to perturbation of their rumen content. Feed intake depression in the first 2 weeks after transfer resulted in short-term changes in milk production, methane emission, fatty acid composition and rumen bacterial community composition. These effects were more pronounced in two cows, whose microbiome composition showed reduced diversity. The fermentation metrics and microbiome diversity of the other two cows were not affected. Their rumen bacterial community initially resembled the composition of the donor but evolved to a new community profile that resembled neither the donor nor their original composition. Descriptive data presented in the current paper show that the rumen bacterial community composition can quickly recover from a reduction in microbiome diversity after a severe perturbation. In contrast to the bacteria, methanogenic communities were more stable over time and unaffected by stress or host effects.

Rumen microbiome profiling uses 16S rRNA (18S rRNA, internal transcribed spacer) gene sequencing, a method that usually sequences a small portion of a single gene and is often biased and varies between different laboratories. Functional information can be inferred from this data, but only for those that are closely related to known annotated species, and even then may not truly reflect the function performed within the environment being studied. Genome sequencing of isolates and metagenome-assembled genomes has now reached a stage where representation of the majority of rumen bacterial genera are covered, but this still only represents a portion of rumen microbial species. The creation of a microbial genome (bins) database with associated functional annotations will provide a consistent reference to allow mapping of RNA-Seq reads for functional gene analysis from within the rumen microbiome. The integration of multiple omic analytics is linking functional gene activity, metabolic pathways and rumen metabolites with the responsible microbiota, supporting our biological understanding of the rumen system. The application of these techniques has advanced our understanding of the major microbial populations and functional pathways that are used in relation to lower methane emissions, higher feed efficiencies and responses to different feeding regimes. Continued and more precise use of these tools will lead to a detailed and comprehensive understanding of compositional and functional capacity and design of techniques for the directed intervention and manipulation of the rumen microbiota towards a desired state.

Dietary and ruminal factors modify the ruminal biohydrogenation (RBH) of polyunsaturated fatty acids (FA), with duodenal FA flows being quantitatively and qualitatively different from FA intake. Using a meta-analysis approach from a database on duodenal flows of FA in ruminants, this study aimed to determine predictive equations for duodenal and absorbed flows of saturated FA, C18:1, C18:2 and C18:3 isomers, odd- and branched-chain FA (OBCFA), C20:5n-3, C22:5n-3 and C22:6n-3 and to quantify the effects of dietary and digestive factors on those equations. The database was divided into four subsets: forage, seed, vegetable oils or animal fats (oil/fat), and fish products (fish) subsets. Models of duodenal and absorbed FA flows were obtained through variance–covariance analysis. Effects of potential interfering factors (conservation mode and botanical families of forages, lipid source, technological processing of lipid supplements, diet composition and animal characteristics) were analysed. We obtained 83 models for duodenal FA flows as a function of FA intake for saturated FA (C14:0, C16:0 and C18:0), C18:1, C18:2 and C18:3 isomers and seven other models for OBCFA. For the seed/oil/fat subset, intakes of total C18:3, C18:2 and starch content increased the duodenal t11-C18:1 flow with 0.08, 0.16 and 0.005 g/kg of dry matter intake (DMI), respectively, whereas intake level [(DMI×100)/BW] decreased it. The c9c12c15-C18:3 RBH was higher for oil/fat than seed (96.7% v. 94.8%) and a protective effect of Leguminosae v. Gramineae against RBH for that FA appeared in the forage subset. The duodenal C17:0 flow increased with starch content and decreased with ruminal pH, respectively, whereas duodenal iso-C16:0 flow decreased with dietary NDF content for the seed/oil/fat subset. The duodenal C20:5n-3, C22:5n-3 and C22:6n-3 flows depended on their respective intake and the inhibitory effect of C22:6n-3 on duodenal C18:0 flow was quantified. Thirteen models of absorbed FA flows were performed depending on their respective duodenal flows. This study determined the effects of different qualitative and quantitative dietary and digestive factors, allowing for improved predictions of duodenal and absorbed FA flows.

Results of recent in vitro experiments suggest that essential oils (EO) may not only influence ruminal fermentation but also modulate the absorption of cations like Na+, Ca2+ and NH4+ across ruminal epithelia of cattle and sheep through direct interaction with epithelial transport proteins, such as those of the transient receptor potential family. The aim of the current study was to examine this hypothesis by testing the effect of a blend of essential oils (BEO) on cation status and feed efficiency in lactating dairy cows. In the experiment, 72 dairy cows in mid-to-end lactation were divided into two groups of 36 animals each and fed the same mixed ration with or without addition of BEO in a 2×2 cross-over design. Feed intake, milk yield and composition, plasma and urine samples were monitored. Feeding BEO elevated milk yield, milk fat and protein yield as well as feed efficiency, whereas urea levels in plasma and milk decreased. In addition, plasma calcium levels increased significantly upon BEO supplementation, supporting the hypothesis that enhanced cation absorption might contribute to the beneficial effects of these EO.

As the co-enzyme of pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, thiamine plays a critical role in carbohydrate metabolism in dairy cows. Apart from feedstuff, microbial thiamine synthesis in the rumen is the main source for dairy cows. However, the amount of ruminal thiamine synthesis, which is influenced by dietary N levels and forage to concentrate ratio, varies greatly. Notably, when dairy cows are overfed high-grain diets, subacute ruminal acidosis (SARA) occurs and results in thiamine deficiency. Thiamine deficiency is characterised by decreased ruminal and blood thiamine concentrations and an increased blood thiamine pyrophosphate effect to >45 %. Thiamine deficiency caused by SARA is mainly related to the increased thiamine requirement during high grain feeding, decreased bacterial thiamine synthesis in the rumen, increased thiamine degradation by thiaminase, and decreased thiamine absorption by transporters. Interestingly, thiamine deficiency can be reversed by exogenous thiamine supplementation in the diet. Besides, thiamine supplementation has beneficial effects in dairy cows, such as increased milk and component production and attenuated SARA by improving rumen fermentation, balancing bacterial community and alleviating inflammatory response in the ruminal epithelium. However, there is no conclusive dietary thiamine recommendation for dairy cows, and the impacts of thiamine supplementation on protozoa, solid-attached bacteria, rumen wall-adherent bacteria and nutrient metabolism in dairy cows are still unclear. This knowledge is critical to understand thiamine status and function in dairy cows. Overall, the present review described the current state of knowledge on thiamine nutrition in dairy cows and the major problems that must be addressed in future research.

Methane produced from formate is one of the important methanogensis pathways in the rumen. However, quantitative information of CH4 production from formate has been rarely reported. The aim of this study was to characterize the conversion rate (CR) of formic acid into CH4 and CO2 by rumen microorganisms. Ground lucerne hay was incubated with buffered ruminal fluid for 6, 12, 24 and 48 h. Before the incubation, 13C-labeled H13COOH was also supplied into the incubation bottle at a dose of 0, 1.5, 2.2 or 2.9 mg/g of DM substrate. There were no interactions (P>0.05) between dose and incubation time for all variables evaluated. When expressed as an absolute amount (ml in gas sample) or a relative CR (%), both 13CH4 and 13CO2 production quadratically increased (P<0.01) with the addition of H13COOH. The total 13C (13CH4 and 13CO2) CR was also quadratically increased (P<0.01) when H13COOH was added. Moreover, formate addition linearly decreased (P<0.031) the concentrations of NH3-N, total and individual volatile fatty acids (acetate, propionate and butyrate), and quadratically decreased (P<0.014) the populations of protozoa, total methanogens, Methanosphaera stadtmanae, Methanobrevibacter ruminantium M1, Methanobrevibacter smithii and Methanosarcina barkeri. In summary, formate affects ruminal fermentation and methanogenesis, as well as the rumen microbiome, in particular microorganisms which are directly or indirectly involved in ruminal methanogenesis. This study provides quantitative verification for the rapid dissimilation of formate into CH4 and CO2 by rumen microorganisms.

In the current intensive production system, ruminants are often fed high-grain (HG) diets. However, this feeding pattern often causes rumen metabolic disorders and may further trigger laminitis, the exact mechanism is not clear. This study investigated the effect of HG diet feeding on fermentative and microbial changes in the rumen and on the expression of pro-inflammatory cytokines and matrix metalloproteinases (MMPs) in the lamellar tissue. In all, 12 male goats were fed a hay diet (0% grain; n=6) or an HG diet (56.5% grain; n=6). On day 50 of treatment, samples of blood, rumen content, and lamellar tissue of hooves of goats were collected. The data showed that compared with the hay group, HG-fed goats had lower (P<0.05) rumen pH but higher (P<0.05) total volatile fatty acids and lactate in the rumen and higher (P<0.05) lipopolysaccharide (LPS) levels in the rumen and blood. HG diet feeding altered the composition of rumen bacterial community, and correspondingly, the results suggested that their functions in the HG group were also altered. HG diet feeding increased (P<0.05) the expression of interleukin-1β, interleukin-6, tumour necrosis factor-α and MMP-2 mRNA in the lamellar tissues compared with the hay group. Correlation analysis indicated that the expression of pro-inflammatory cytokines were positively correlated with MMP-2 expression in lamellar tissues. Overall, these results revealed that HG feeding altered the patterns of rumen fermentation and the composition and functions of rumen bacterial community, and lead to higher levels of LPS in the peripheral blood, and further activated the inflammatory response in lamellar tissues, which may progress to the level of laminar damage.