SCFA transport in the forestomach of ruminants

Effects of grape seed extract supplementation on the growth performance, nutrients digestion and immunity of weaned lambs

Grape seed extract (GSE) has a variety of biological functions. At present, there has been limited information on the utilization of GSE as a feed additive in weaned lambs. The aim of this experiment was to study the potential influence of dietary supplementation with GSE on the growth performance, rumen fermentation characteristics, apparent digestibility, blood parameters and immunity in weaned lambs. In total, 30 male Hu sheep lambs with similar body weight (15.43 ± 0.49 kg) and age (48 ± 2 days) were randomly divided into two treatments: control (CON, fed basal ration) and GSE [fed basal ration and 0.6 g/d GSE (main compositions: proanthocyanidin 50%, catechin 24%, gallic acid 16% and epicatechin 6%) per lamb]. The feeding experiment lasted for 60 d. Results showed that GSE supplementation significantly increased (p = 0.008) the average daily gain of lambs. Compared with CON group, the ruminal propionate and butyrate concentrations were significantly increased (p < 0.05) in GSE group, whereas the ammonia nitrogen was decreased (p = 0.007). Also, the crude protein, neutral detergent fiber and ether extract digestibility of GSE group were higher (p < 0.05) than those of CON group. The serum contents of glucose, triglyceride, immunoglobulin G, glutathione peroxidase and total antioxidant capacity were significantly increased (p < 0.05) in GSE group when compared to those in CON group. However, an opposite trend of urea nitrogen, non-esterified fatty acid, interleukin-1β, itumor necrosis factor-α and malondialdehyde was observed between the two groups. Additionally, supplementation of GSE increased (p < 0.05) the Lactobacillus and decreased (p < 0.05) the Escherichia coli and Salmonella counts in the feces of lambs. In summary, GSE supplementation can improve growth performance, nutrient digestion and immunity of weaned lambs.

Dung treated by high-temperature composting is an optimal bedding material for suckling calves according to analyses of microbial composition, growth performance, health status, and behavior

Bedding materials are important for suckling buffalo calves. Treated dung has been used as a bedding material for dairy cows but the lack of an appropriate safety assessment limits its application. In this study, we evaluated the feasibility of treated dung (TD) as a bedding material for suckling calves by comparing TD with rice husk (RH) and rice straw (RS) bedding materials. The TD was prepared through high-temperature composting by Bacillus subtilis. Thirty-three newborn suckling buffalo calves (Bubalus bubalis, 40.06 ± 5.79 kg) were randomly divided into 3 bedding material groups (TD, RH, and RS) and bedded with 1 of the 3 bedding materials for 60 d. We compared cost, moisture content, bacterial counts, and microbial composition of the 3 bedding materials, and investigated growth performance, health status, behavior, rumen fermentation, and blood parameters of bedded calves. The results showed that TD contained the fewest gram-negative bacteria and coliforms on d 1 and 30 and the lowest relative abundance of Staphylococcus throughout the experiment. The RH and TD bedding materials had the lowest cost. Calves in the TD and RS groups showed a higher dry matter intake, and final body weight and average daily gain in the TD and RS groups tended to be higher than in the RH group. Calves in the TD and RS groups had a lower disease incidence (diarrhea and fever), fewer antibiotic treatments, and lower fecal score than calves in the RH group. Higher contents of IgG, IgA, and IgM were observed in calves of the TD and RS groups than in calves of the RH group on d 10, indicating higher immune ability in TD and RS groups. Furthermore, TD bedding increased the butyric acid content in the calf's rumen, whereas RS bedding increased the acetate content, which might be attributed to the longer time and higher frequency of eating bedding material in the RS group. Considering all of the above indicators, we concluded that TD is the optimal bedding material for calves based on economics, bacterial count, microbial diversity, growth performance, and health status. Our findings provide a valuable reference for bedding material choice and calf farming.

Rumen protozoa population and carbohydrate-digesting enzymes in sheep fed a diet supplemented with hydrolysable tannins

The aim of the study was to compare the effect of adding different sources of hydrolysable tannins to the sheep diet on protozoa population and carbohydrate digestion in the rumen. The study was performed in 3 Polish Lowland ewes fistulated to the rumen in a 3 × 3 Latin -square design. Control sheep (CON) received (g/d): meadow hay (600), barley meal (300), soybean meal (100) and vitamin-mineral premix (20). Sheep from the experimental groups were additionally administered 12.6 g/kg DM oak bark extract (OAK) and 3.91 g/kg DM tannic acid (TAN). The net consumption of tannins was approx. 0.4% DM for both additives. Regarding the count of protozoa, a significant interaction between diet and sampling time was documented for all ciliates (P<0.01), with a significant effect of both factors when considered separately. Experimental diets reduced the number of total protozoa and Entodinium spp. (before, 2 and 4 h after feeding; P<0.01), while increasing the abundance of Isotricha spp. population (4 h after feeding; P<0.01) in the rumen. Interestingly, the count of Ophryoscolex spp. after feeding the TAN diet increased before feeding and 2 h after feeding in comparison to the CON and OAK groups, respectively, and subsequently decreased compared to the CON diet (4 and 8 h after feeding, P<0.01). A significant interaction between the diet and sampling time was observed for xylanolytic activity (P<0.01) in the rumen, with a significant effect of sampling time, which decreased its activity in CON (after feeding) and OAK sheep (2 h after feeding; P<0.01). For amylolytic activity (P<0.10), there was a trend towards a significant interaction between experimental factors, with a significant effect on both diet and sampling time. Detailed analysis showed that the TAN diet significantly reduced amylolytic activity 2 h after feeding compared to the CON group (P<0.05). In conclusion, the TAN diet significantly reduced the number of total protozoa and Entodinium spp., which consequently reduced amylolytic activity in the rumen, without any significant effect on pH and carbohydrate fermentation in the rumen.

The intraruminal redox potential is stabilised by opposing influences during fermentation

An optimal fermentation process in the forestomach is pivotal for the wellbeing and performance of ruminants. Complex carbohydrates are broken down into short-chain fatty acids (SCFA) which form the major energy source for the animal. A strong interrelationship of this process with intraruminal pH and redox potential (Eh) exists. These parameters can be measured with intraruminal sensors, but the interpretation of the measurements, especially of Eh, and their meaning for intraruminal homeostasis is not completely clear. In this study, factors influencing intraruminal Eh were elucidated. We hypothesised that intraruminal Eh is influenced by the fermentation process as such, but not by its end products SCFA. We measured Eh and pH in ruminal fluid from fasting cannulated sheep after the addition of 0.06 m Na-acetate, -propionate, -butyrate or glucose in vitro. Furthermore, we assessed the interrelation of pH and Eh. Basal Eh and pH values were -120 ± 41 mV and 7.0 ± 0.3, respectively, in native ruminal fluid in vitro. While the addition of SCFA did not induce any changes, glucose addition caused a significant decrease in both pH and Eh compared to the values before the addition (paired Student's t-test, p < 0.05). We attribute the decrease in Eh to an increased production of H₂ in the process of generating SCFA, predominantly acetate. By titrating both native and particle-free ruminal fluid to more acidic and basic pH values (4.5-8.5), we found a non-linear inverse correlation of pH and Eh, counteracting the H₂ -driven decrease of Eh during fermentation. Thus, the intraruminal Eh is influenced by pH and H₂ output during SCFA formation. The opposed character of these factors stabilises the intraruminal homeostasis which might help maintain symbiotic microbiota in the rumen. Understanding, monitoring, and supporting this system will be an essential part of modern cattle production.

Gastrointestinal Biogeography of Luminal Microbiota and Short-Chain Fatty Acids in Sika Deer (Cervus nippon)

The gut microbiota of sika deer has been widely investigated, but the spatial distribution of symbiotic microbes among physical niches in the gastrointestinal tract remains to be established. While feces are the most commonly used biological samples in these studies, the accuracy of fecal matter as a proxy of the microbiome at other gastrointestinal sites is as yet unknown. In the present study, luminal contents obtained along the longitudinal axis of deer gastrointestinal tract (rumen, reticulum, omasum, abomasum, small intestine, cecum, colon, and rectum) were subjected to 16S rRNA gene sequencing for profiling of the microbial composition, and samples from the rumen, small intestine, and cecum were subjected to metabolomic analysis to evaluate short-chain fatty acid (SCFA) profiles. Prevotella bacteria were the dominant gastric core microbes, while Christensenellaceae_R-7_group was predominantly observed in the intestine. While the eight gastrointestinal sites displayed variations in microbial diversity, abundance, and function, they could be clustered into stomach, small intestine, and large intestine segments, and the results further highlighted a specific microbial niche of the small intestine. SCFA levels in the rumen, small intestine, and cecum were significantly different, with Bacteroidetes and Spirochaetes were shown to play a critical role in SCFA production. Finally, the rectal microbial composition was significantly correlated with colonic and cecum communities but not those of the small intestine and four gastric sites. Quantification of the compositions and biogeographic relationships between gut microbes and SCFAs in sika deer should provide valuable insights into the interactions contributing to microbial functions and metabolites. IMPORTANCE Feces or specific segments of the gastrointestinal tract (in particular, the rumen) were sampled to explore the gut microbiome. The gastrointestinal biogeography of the luminal microbiota in ruminants, which is critical to guide accurate sampling for different purposes, is poorly understood at present. The microbial community of the rectal sample (as a proxy of fecal sample) showed higher correlation with those of other large intestinal sites relative to the small intestine or stomach, suggesting that the microbial composition is specifically shaped by the unique physiological characteristics of different gastrointestinal niches. In addition, significant differences in microbiomes and SCFAs were observed among the different gastrointestinal sites.

Active dry yeast supplementation improves the growth performance, rumen fermentation, and immune response of weaned beef calves

The objective of this experiment was to investigate the potential benefits of active dry yeast (ADY) on the growth performance, rumen fermentation, nutrient digestibility, and serum parameters of weaned beef calves. Thirty Simmental crossbred male calves (body weight = 86.47 ± 4.41 kg and 70 ± 4 d of age) were randomly divided into 2 groups: control (CON) (fed basal ration) and ADY (fed basal ration and 5 g/d ADY per calf). The dietary concentrate-to-roughage ratio was 35:65. All the calves were regularly provided rations 3 times a day at 07:00, 13:00, and 19:00 and had free access to water. The experiment lasted for 60 d. The average daily gain of ADY group was higher (P = 0.007) than that of the CON group, and the ratio of feed intake to average daily gain in the ADY group was reduced (P = 0.022) as compared to the CON group. The concentration of ruminal ammonia-N was higher (P = 0.023) in the CON group than that in the ADY group, but an opposite trend of microbial protein was found between the 2 groups. Also, the ruminal concentrations of propionate and butyrate were higher (P < 0.05) in the ADY group than those in the CON group. Calves fed ADY exhibited higher (P < 0.05) crude protein and neutral detergent fiber digestibility. Supplementation of ADY increased (P < 0.05) the contents of glucose, glutathione peroxidase, superoxide dismutase, immunoglobulin A, immunoglobulin M, and interleukin 10 in the serum of calves, but an opposite trend was observed in malondialdehyde, interleukin 1 beta, and tumor necrosis factor alpha contents between the 2 groups. In conclusion, dietary supplementation with ADY could improve the growth performance, rumen fermentation, nutrient digestibility, antioxidant ability, and immune response of weaned beef calves.

Comparative study of growth performance, nutrient digestibility, and ruminal and fecal bacterial community between yaks and cattle-yaks raised by stall-feeding

The experiment was conducted to compare the growth performance, rumen fermentation, nutrient digestibility, and ruminal and fecal bacterial community between yaks and cattle-yaks. Ten male yaks (36-month-old) were used as the yak (YAK) group and 10 male cattle-yaks with similar age were selected as the cattle-yak (CAY) group. All the animals were fed same ration and the experiment lasted for 60 days. The results showed that the average daily gain and dry matter intake of CAY group were higher (P < 0.05) than those of YAK group. The ruminal concentrations of total volatile fatty acids, acetate, and butyrate were higher (P < 0.05) in CAY group than those in YAK group. However, the neutral detergent fiber and acid detergent fiber digestibility exhibited an opposite between two groups. In the rumen, the relative abundances of Prevotella 1 and Prevotellaceae UCG-001 were higher (P < 0.05) and Succiniclasticum and Butyrivibrio 2 were lower (P < 0.05) in YAK group compared to CAY group. In the feces, the unclassified Lachnospiraceae, Lachnospiraceae NK4A136 group, and Lachnospiraceae AC2044 group were significantly enriched (P < 0.05) in YAK group, whereas the Ruminococcaceae UCG-010, Ruminococcaceae UCG-013, and Succiniclasticum were significantly enriched (P < 0.05) in CAY group. Overall, under the same diet, the yaks have higher fiber utilization and cattle-yaks have higher energy utilization.

Carbonic anhydrase influences asymmetric sodium and acetate transport across omasum of sheep

Objective

Omasum is an important site for the absorption of short chain fatty acids. The major route for the transport of acetate is via sodium hydrogen exchanger (NHE). However, a discrepancy in the symmetry of sodium and acetate transport has been previously reported, the mechanism of which is unclear. In this study, we investigated the possible role of carbonic anhydrase (CA) for this asymmetry.

Methods

Omasal tissues were isolated from healthy sheep (N = 3) and divided into four groups; pH 7.4 and 6.4 alone and in combination with Ethoxzolamide. Electrophysiological measurements were made using Ussing chamber and the electrical measurements were made using computer controlled voltage clamp apparatus. Effect(s) of CA inhibitor on acetate and sodium transport flux rate of Na²² and ¹⁴C-acetate was measured in three different flux time periods. Data were presented as mean±standard deviation and level of significance was ascertained at p≤0.05.

Results

Mucosal to serosal flux of Na (J_msNa) was greater than mucosal to serosal flux of acetate (J_msAc) when the pH was decreased from 7.4 to 6.4. However, the addition of CA inhibitor almost completely abolished this discrepancy (J_msNa ≈ J_msAc).

Conclusion

The results of the present study suggest that the additional protons required to drive the NHE were provided by the CA enzyme in the isolated omasal epithelium. The findings of this study also suggest that the functions of CA may be exploited for better absorption in omasum.

Influence of fumaric acid on ruminal parameters and organ weights of growing bulls fed with grass or maize silage

The influence of the potential methane reducer, fumaric acid (FA), on ruminal parameters, the rumen wall and organ weights was investigated in a long-term study with growing bulls. In all, 20 bulls were fed with maize or grass silage as roughage, and with concentrate with or without 300 g FA per animal and day during the whole fattening period. After slaughtering, the organs were weighed and blood serum was analysed for glucose, β-hydroxybutyric acid (BHB) and non-esterified fatty acid concentration. The ruminal fluid was analysed for short-chain fatty acids, ammonia-N and the microbial community via single strand conformation polymorphism analysis. The rumen wall was examined histopathologically and results were graded as 'no visible lesions', 'few inflammatory infiltrates', 'some inflammatory infiltrates' or 'several inflammatory infiltrates'. In addition, the dimensions of the rumen villi were measured. The FA supplementation decreased the serum BHB concentration and the butyric acid concentration in the ruminal fluid. The microbial community in the ruminal fluid was not influenced by FA. An interaction between FA and silage type was observed for the inflammation centres counted in the villous area of rumen papillae. This interaction was also observed in the length and surface of the rumen villi. Rumen villi results show that the influence of FA depends on the roughage used in the diet.

Effects of Saccharomyces cerevisiae fermentation products on dairy calves: Ruminal fermentation, gastrointestinal morphology, and microbial community

The aim of this study was to evaluate the effects of Saccharomyces cerevisiae fermentation products (SCFP) in the calf starter and milk on ruminal fermentation, gastrointestinal morphology, and microbial community in the first 56 d of life. Thirty Holstein bull calves were randomly assigned to 1 of 3 groups: a texturized calf starter containing 0 (CON), 0.5, or 1% SCFP (XPC, Diamond V, Cedar Rapids, IA) of dry matter from d 4 to 56. In addition, the XPC-supplemented calves were fed with 1 g/d SCFP (SmartCare, Diamond V, Cedar Rapids, IA) in milk from d 2 to 30. All calves were fed 4 L of colostrum within 1 h of birth and were subsequently fed milk twice daily until weaned on d 56. Rumen fluid was collected by an esophageal tube 4 h after the morning feeding on d 28 and 56 to determine ruminal pH, ammonia-N, and volatile fatty acids concentrations. On d 56, 15 (5 per treatment) calves were harvested and slaughter weight, gastrointestinal morphology parameters, and bacteria community were recorded. Papilla length, width, and surface area were measured from 5 locations within the rumen. Villus height, width, surface area, crypt depth, and villus height-to-crypt depth ratio were measured in the duodenum, jejunum, and ileum. Next-generation sequencing technology was used to test the microbial community of the rumen and duodenum samples on d 28 and 56. Data were analyzed by MIXED procedure in SAS (SAS Institute Inc., Cary, NC) with contrast statements to declare CON versus all SCFP and 0.5 versus 1% SCFP in starter grains. Ruminal pH, ammonia-N, and total volatile fatty acids were not altered by SCFP. However, the supplemented groups exhibited higher ruminal butyrate concentrations coinciding with higher Butyrivibrio and lower Prevotella richness than CON group. Supplementation of SCFP increased papilla length in the rumen. In the small intestine, SCFP reduced crypt depth of jejunum, and increased villus height-to-crypt depth ratio in all segments of the small intestine, especially when supplemented at a higher dosage in the starter. In conclusion, Saccharomyces cerevisiae fermentation products improved gastrointestinal morphology, possibly due to increased Butyrivibrio and decreased Prevotella richness of the rumen fluid, which resulted in an increase in butyrate production, and the effect was slightly greater with the higher dosage of SCFP in the starter.

Transcriptome differences in the rumen of beef steers with variation in feed intake and gain

BACKGROUND

Feed intake and gain are economically important traits in beef production. The rumen wall interacts with feed, microbial populations, and fermentation products important to cattle nutrition. As such, it is likely to be a critical component in the beef steer's ability to utilize feedstuffs efficiently. To identify genes associated with steer feed intake and body weight gain traits, and to gain an understanding of molecules and pathways involved in feed intake and utilization, RNA sequencing (RNA-Seq) was performed on rumen papillae from 16 steers with variation in gain and feed intake. Four steers were chosen from each of the four Cartesian quadrants for gain×feed intake and used to generate individual RNA-Seq libraries.

RESULTS

Normalized read counts from all of the mapped reads from each of the four groups of animals were individually compared to the other three groups. In addition, differentially expressed genes (DEGs) between animals with high and low gain, as well as high and low intake were also evaluated. A total of 931 genes were differentially expressed in the analyses of the individual groups. Eighty-nine genes were differentially expressed between high and low gain animals; and sixty-nine were differentially expressed in high versus low intake animals. Several of the genes identified in this study have been previously associated with feed efficiency. Among those are KLK10, IRX3, COL1A1, CRELD2, HDAC10, IFITM3, and VIM.

CONCLUSIONS

Many of the genes identified in this study are involved with immune function, inflammation, apoptosis, cell growth/proliferation, nutrient transport, and metabolic pathways and may be important predictors of feed intake and gain in beef cattle.

Bicarbonate-dependent transport of acetate and butyrate across the basolateral membrane of sheep rumen epithelium

AIM

This study aimed to assess the role of HCO₃⁻ in the transport of acetate and butyrate across the basolateral membrane of rumen epithelium and to identify transport proteins involved.

METHODS

The effects of basolateral variation in HCO₃⁻ concentrations on acetate and butyrate efflux out of the epithelium and the transepithelial flux of these short-chain fatty acids were tested in Ussing chamber experiments using (14)C-labelled substrates. HCO₃⁻-dependent transport mechanisms were characterized by adding specific inhibitors of candidate proteins to the serosal side.

RESULTS

Effluxes of acetate and butyrate out of the epithelium were higher to the serosal side than to the mucosal side. Acetate and butyrate effluxes to both sides of rumen epithelium consisted of HCO₃⁻-independent and -dependent parts. HCO₃⁻-dependent transport across the basolateral membrane was confirmed in studies of transepithelial fluxes. Mucosal to serosal fluxes of acetate and butyrate decreased with lowering serosal HCO₃⁻ concentrations. In the presence of 25 mm HCO₃⁻, transepithelial flux of acetate was inhibited effectively by p-hydroxymercuribenzoic acid or α-cyano-4-hydroxycinnamic acid, while butyrate flux was unaffected by the blockers. Fluxes of both acetate and butyrate from the serosal to the mucosal side were diminished largely by the addition of NO₃⁻ to the serosal side, with this effect being more pronounced for acetate.

CONCLUSION

Our results indicate the existence of a basolateral short-chain fatty acid/HCO₃⁻ exchanger, with monocarboxylate transporter 1 as a primary candidate for acetate transfer.

Identification of differentially expressed proteins in ruminal epithelium in response to a concentrate-supplemented diet

Ruminal epithelium adapts to dietary change with well-coordinated alterations in metabolism, proliferation, and permeability. To further understand the molecular events controlling diet effects, the aim of this study was to evaluate protein expression patterns of ruminal epithelium in response to various feeding regimes. Sheep were fed with a concentrate-supplemented diet for up to 6 wk. The control group received hay only. Proteome analysis with differential in gel electrophoresis technology revealed that, after 2 days, 60 proteins were significantly modulated in ruminal epithelium in a comparison between hay-fed and concentrate-fed sheep (P < 0.05). Forty proteins were upregulated and 20 proteins were downregulated in response to concentrate diet. After 6 wk of this diet, only 14 proteins were differentially expressed. Among these, 11 proteins were upregulated and 3 downregulated. To identify proteins that were modulated by dietary change, two-dimensional electrophoresis was coupled with liquid chromatography electrospray ionization mass spectrometry. The differential expression of selected proteins, such as esterase D, annexin 5, peroxiredoxin 6, carbonic anhydrase I, and actin-related protein 3, was verified by immunoblotting and/or mRNA analysis. The identified proteins were mainly associated with functions related to cellular stress, metabolism, and differentiation. These results suggest new candidate proteins that may contribute to a better understanding of the signaling pathways and mechanisms that mediate rumen epithelial adaptation to high-concentrate diet.

Evidence for NHE3-mediated Na transport in sheep and bovine forestomach

Na absorption across the cornified, multilayered, and squamous rumen epithelium is mediated by electrogenic amiloride-insensitive transport and by electroneutral Na transport. High concentrations of amiloride (>100 μM) inhibit Na transport, indicating Na+/H+ exchange (NHE) activity. The underlying NHE isoform for transepithelial Na absorption was characterized by mucosal application of the specific inhibitor HOE642 for NHE1 and S3226 for NHE3 in Ussing chamber studies with isolated epithelia from bovine and sheep forestomach. S3226 (1 μM; NHE3 inhibitor) abolished electroneutral Na transport under control conditions and also the short-chain fatty acid-induced increase of Na transport via NHE. However, HOE642 (30 μM; NHE1 inhibitor) did not change Na transport rates. NHE3 was immunohistochemically localized in membranes of the upper layers toward the lumen. Expression of NHE1 and NHE3 has been previously demonstrated by RT-PCR, and earlier experiments with isolated rumen epithelial cells have shown the activity of both NHE1 and NHE3. Obviously, both isoforms are involved in the regulation of intracellular pH, pHi. However, transepithelial Na transport is only mediated by apical uptake via NHE3 in connection with extrusion of Na by the basolaterally located Na-K-ATPase. The missing involvement of NHE1 in transepithelial Na transport suggests that the proposed “job sharing” in epithelia between these two isoforms probably also applies to forestomach epithelia: NHE3 for transepithelial transport and NHE1 for, among others, pHi and volume regulation.

Role of colonic short-chain fatty acid transport in diarrhea

Short-chain fatty acids (SCFA) are the major anion in stool and are synthesized from nonabsorbed carbohydrate by the colonic microbiota. Nonabsorbed carbohydrate are not absorbed in the colon and induce an osmotically mediated diarrhea; in contrast, SCFA are absorbed by colonic epithelial cells and stimulate Na-dependent fluid absorption via a cyclic AMP-independent process involving apical membrane Na-H, SCFA-HCO(3), and Cl-SCFA exchanges. SCFA production represents an adaptive process to conserve calories, fluid, and electrolytes. Inhibition of SCFA synthesis by antibiotics and administration of PEG, a substance that is not metabolized by colonic microbiota, both result in diarrhea. In contrast, increased production of SCFA as a result of providing starch that is relatively resistant to amylase digestion [so-called resistant starch (RS)] to oral rehydration solution (RS-ORS) improves the efficacy of ORS and represents an important approach to improve the effectiveness of ORS in the treatment of acute diarrhea in children under five years of age.

The effect and mode of action of saponins on the microbial populations and fermentation in the rumen and ruminant production

The growing public concerns over chemical residues in animal-derived foods and threats of antibiotic-resistant bacteria have renewed interest in exploring safer alternatives to chemical feed additives in ruminant livestock. Various bioactive phytochemicals including saponins appear to be potential 'natural' alternatives to 'chemical' additives in modulating rumen fermentation favourably and animal performance. Saponins are a diverse group of glycosides present in many families of plants. The primary effect of saponins in the rumen appears to be to inhibit the protozoa (defaunation), which might increase the efficiency of microbial protein synthesis and protein flow to the duodenum. Furthermore, saponins may decrease methane production via defaunation and/or directly by decreasing the activities (i.e. rate of methanogenesis or expression of methane-producing genes) and numbers of methanogens. Saponins may also selectively affect specific rumen bacteria and fungi, which may alter the rumen metabolism beneficially or adversely. The ammonia-adsorption and modulation of digesta passage in the rumen by saponins have also been implicated in altering rumen metabolism, but their physiological responses are likely to be negligible compared with microbiological effects. The effects of saponins on rumen fermentation have not been found to be consistent. These discrepancies appear to be related to the chemical structure and dosage of saponins, diet composition, microbial community and adaptation of microbiota to saponins. There is need for systematic research based on chemical structures of saponins, nutrient composition of diets and their effects on rumen microbial ecosystem to obtain consistent results. The present paper reviews and discusses the effects and mode of action of saponins on microbial community and fermentation in the rumen, and ruminant performance.

Perspectives on ruminant nutrition and metabolism I. Metabolism in the Rumen

Advances in knowledge of ruminant nutrition and metabolism during the second half of the twentieth century have been reviewed. Part I is concerned with metabolism in the rumen: Part II discusses utilization of nutrients absorbed from the rumen and lower tract to support growth and reproduction. The time frame was prompted by the crucial advances in ruminant physiology which arose from the work of Sir Jospeh Barcroft and his colleagues at Cambridge in the 1940s and 50s, and by the brilliant studies of Robert Hungate on rumen microbiology at much the same time.

In reviewing the growth of knowledge of the role of bacteria, protozoa, fungi and bacteriophages in the rumen, outstanding developments have included the identification and characterization of fungi and the recognition that the utilization of polysaccharides in the rumen is accomplished by the sequential activities of consortia of rumen microorganisms. The role of protozoa is discussed in relation to the long standing debate on whether or not the removal of protozoa (defaunation) improves the efficiency of ruminant production. In relation to nitrogen (N) metabolism, the predation of bacteria by protozoa increases protein turnover in the rumen and reduces the efficiency of microbial protein production. This may account for the beneficial effects of defaunation where dietary N intakes are low and possibly rate limiting for growth and production.

Current approaches to the measurement of rates of production of short chain fatty acids (SCFA) in the rumen based on the mathematical modelling of isotope dilution data are outlined. The absorption of SCFA from the rumen and hindgut is primarily a passive permeation process.

The role of microorganisms in N metabolism in the rumen has been discussed in relation to ammonia and urea interrelationships and to current inadequacies in the measurement of both protein degradation in the rumen and microbial protein synthesis. The growth of knowledge of digestion and absorption of dietary lipids has been reviewed with emphasis on the antimicrobial activity of lipids and the biohydrogenation of unsaturated fatty acids. The protection of unsaturated dietary fats from ruminal biohydrogenation is an approach to the manipulation of the fatty acid composition of meat and dairy products.

Discussion of the production of toxins in the rumen and the role of microorganisms in detoxification has focused on the metabolism of oxalate, nitrate, mycotoxins, saponins and the amino acid mimosine. Mimosine occurs in the tropical shrub leucaena, which is toxic to cattle in Australia but not in Hawaii. Tolerance to leucaena stems from the presence of a bacterium found in the rumen of Hawaiian cattle, which when transferred to Australian cattle survives and confers protection from mimosine. The genetic modification of rumen microorganisms to improve their capacity to ultilize nutrients or to detoxify antinutritive factors is an attractive strategy which has been pursued with outstanding success in the case of fluoroacetate. A common rumen bacterium has been genetically modified to express the enzyme fluoroacetate dehalogenase. The modified organism has been shown to survive in the rumen at metabolically significant levels and to confer substantial protection from fluoroacetate poisoning.

Absorption of short-chain fatty acids, sodium and water from the forestomach of camels

In camelids the ventral parts of compartments 1 and 2 (C1/C2) and the total surface of compartment 3 of the forestomach are lined with tubular glands, whereas in ruminants the surface of the forestomach is composed entirely of stratified, squamous epithelium. Thus, differences in absorption rates between these foregut fermenters can be expected. In five camels C1/C2 was temporarily isolated, washed and filled with buffer solutions. Absorption of short-chain fatty acids (SCFA) and net absorption of sodium and water were estimated relative to Cr-ethylenediaminetetraacetic acid as a fluid marker. SCFA were extensively absorbed in the forestomach; clearance rates of SCFA with different chain lengths were equal. After lowering the pH of solutions SCFA absorption rates increased, but much less than the increase of the non-ionized fraction. Absorption of propionate was lower when acetate had been added. Findings suggest that most of the SCFA in camels are transported in the ionized form, most likely via an anion exchange mechanism. Net water absorption is closely related to net sodium absorption. Apparently water absorption results from an iso-osmotic process. Differences between absorption mechanisms of SCFA from the forestomach of camelids and ruminants are discussed.

Expression, cellular localization, and functional role of monocarboxylate transporter 4 (MCT4) in the gastrointestinal tract of ruminants

This is the first study to determine the precise cellular localization of monocarboxylate transporter 4 (MCT4), along with its co-existence with its chaperone, CD147 in the ruminant gastrointestinal tract. Quantitative Western blot analysis demonstrated that the abundance of MCT4 protein was in the order of forestomach > large intestine > abomasum >or= small intestine. Immunohistochemistry and immunofluorescence confocal laser microscopy showed that MCT4 in the forestomach was confined to the cell membranes of strata corneum and granulosum, while diffuse cytoplasmic staining for MCT4 was visualized in strata spinosum and basale. In the epithelium cells lining the abomasum, MCT4 immunoreactive positivities were predominantly localized on the basolateral membranes. In the small intestine, MCT4 was localized at the brush borders and the basolateral membranes of the epithelial cells lining the villi, however it was mostly found on the apical membranes of the crypt cells. In the large intestine, the immunoreactivity for MCT4 differed between the surface epithelium and the crypts; in the surface epithelium, MCT4 was mainly localized at the apical membranes, whereas in the crypts it was predominantly expressed on the basolateral membranes of the lining epithelial cells. MCT4 was remarkably co-existed with CD147 along the bovine gastrointestinal tract. Our results suggest that MCT4 can play an important role in the transport of SCFA. The study also explored the potential functional collaboration between MCT1 and MCT4 and provided new insights into the mechanisms that mediate the transport of SCFA and other monocarboxylates in the different segments of the ruminant gastrointestinal tract.

Monocarboxylate transporter 1 (MCT1) plays a direct role in short-chain fatty acids absorption in caprine rumen

Despite the importance of short-chain fatty acids (SCFA) in maintaining the ruminant physiology, the mechanism of SCFA absorption is still not fully studied. The goal of this study was to elucidate the possible involvement of monocarboxylate transporter 1 (MCT1) in the mechanism of SCFA transport in the caprine rumen, and to delineate the precise cellular localization and the level of MCT1 protein along the entire caprine gastrointestinal tract. RT-PCR revealed the presence of mRNA encoding for MCT1 in all regions of the caprine gastrointestinal tract. Quantitative Western blot analysis showed that the level of MCT1 protein was in the order of rumen >/= reticulum > omasum > caecum > proximal colon > distal colon > abomasum > small intestine. Immunohistochemistry and immunofluorescence confocal analyses revealed widespread immunoreactive positivities for MCT1 in the caprine stomach and large intestine. Amongst the stratified squamous epithelial cells of the forestomach, MCT1 was predominantly expressed on the cell boundaries of the stratum basale and stratum spinosum. Double-immunofluorescence confocal laser-scanning microscopy confirmed the co-localization of MCT1 with its ancillary protein, CD147 in the caprine gastrointestinal tract. In vivo and in vitro functional studies, under the influence of the MCT1 inhibitors, p-chloromercuribenzoate (pCMB) and p-chloromercuribenzoic acid (pCMBA), demonstrated significant inhibitory effect on acetate and propionate transport in the rumen. This study provides evidence, for the first time in ruminants, that MCT1 has a direct role in the transepithelial transport and efflux of the SCFA across the stratum spinosum and stratum basale of the forestomach toward the blood side.

Monocarboxylate transporter 1 (MCT1) mediates transport of short-chain fatty acids in bovine caecum

The present study was undertaken to investigate the functional role of monocarboxylate transporter 1 (MCT1) in the ruminant large intestine. Messenger RNA encoding for MCT1 was verified by reverse transcriptase-polymerase chain reaction in caecum, proximal colon and distal colon of adult cattle. Both immunohistochemistry and confocal laser microscopy verified that the MCT1 protein was abundant in the surface epithelium of the large intestine, and the amount decreased from the opening of the crypt to its base. In the immunopositive cells, MCT1 was primarily localized in the basolateral membranes of epithelium lining the large intestine. Western blotting indicated that the levels of MCT1 protein were highest in the caecum, followed by proximal colon and then distal colon. In vitro studies were conducted to elucidate the possible involvement of MCT1 in the transport of short-chain fatty acids (SCFA) across the isolated mucosal sheets of cattle caecum using the Ussing chamber technique. Acetate absorption was found to be pH dependent, and the rate of acetate absorption increased as pH decreased. The serosal application of the MCT1 inhibitor 'p-chloromercuribenzoic acid (pCMB)' significantly reduced the transport of acetate across the caecal epithelium of cows. In addition, the transport of acetate was significantly reduced in the presence of its analogue, propionate, indicating that acetate and propionate compete for binding to the same transporter. The results show that MCT1 is a major route for SCFA efflux across the basolateral membrane of bovine large intestine and that it could play a role in the regulation of intracellular pH.

Monocarboxylate transporter 1 gene expression in the ovine gastrointestinal tract

In this study, we investigated the tissue distribution and expression of monocarboxylate transporter 1 (MCT1) along the gastrointestinal tract of sheep. Western blot analysis suggested the presence of MCT1 as a 43-kDa protein in immunoblots of membranes from the various tissues examined. The results of Western blotting were further confirmed by immunohistochemical studies, which revealed intense immunoreactivity for the MCT1 protein in the forestomach (rumen, reticulum and omasum) and large intestine (caecum, proximal and distal colon). Moderate reactivity, however, was detected in the abomasum, while no immunoreactivity could be seen in any regions of the small intestine examined. Furthermore, MCT1 was expressed at the mRNA level as determined by reverse transcriptase polymerase chain reaction (RT-PCR), which showed a band of the expected size (300 bp) in all tissues examined. From these results we concluded that MCT1 protein is highly expressed and distributed in the stomach and large intestine of sheep suggesting that MCT1 may play a significant role in the transport of short chain fatty acids and their metabolites in the gastrointestinal tract of ruminants.

Modulation of electroneutral Na transport in sheep rumen epithelium by luminal ammonia

Ammonia is an abundant fermentation product in the forestomachs of ruminants and the intestine of other species. Uptake as NH3 or NH4+ should modulate cytosolic pH and sodium-proton exchange via Na+/H+ exchanger (NHE). Transport rates of Na+, NH4+, and NH3 across the isolated rumen epithelium were studied at various luminal ammonia concentrations and pH values using the Ussing chamber method. The patch-clamp technique was used to identify an uptake route for NH4+. The data show that luminal ammonia inhibits electroneutral Na transport at pH 7.4 and abolishes it at 30 mM (P < 0.05). In contrast, at pH 6.4, ammonia stimulates Na transport (P < 0.05). Flux data reveal that at pH 6.4, approximately 70% of ammonia is absorbed in the form of NH4+, whereas at pH 7.4, uptake of NH3 exceeds that of NH4+ by a factor of approximately four. The patch-clamp data show a quinidine-sensitive permeability for NH4+ and K+ but not Na+. Conductance was 135 +/- 12 pS in symmetrical NH(4)Cl solution (130 mM). Permeability was modulated by the concentration of permeant ions, with P(K) > P(NH4) at high and P(NH4) > P(K) at lower external concentrations. Joint application of both ions led to anomalous mole fraction effects. In conclusion, the luminal pH determines the predominant form of ammonia absorption from the rumen and the effect of ammonia on electroneutral Na transport. Protons that enter the cytosol through potassium channels in the form of NH4+ stimulate and nonionic diffusion of NH3 blocks NHE, thus contributing to sodium transport and regulation of pH.

UT-B is expressed in bovine rumen: potential role in ruminal urea transport

The UT-A (SLC14a2) and UT-B (SLC14a1) genes encode a family of specialized urea transporter proteins that regulate urea movement across plasma membranes. In this report, we describe the structure of the bovine UT-B (bUT-B) gene and characterize UT-B expression in bovine rumen. Northern analysis using a full-length bUT-B probe detected a 3.7-kb UT-B signal in rumen. RT-PCR of bovine mRNA revealed the presence of two UT-B splice variants, bUT-B1 and bUT-B2, with bUT-B2 the predominant variant in rumen. Immunoblotting studies of bovine rumen tissue, using an antibody targeted to the NH2-terminus of mouse UT-B, confirmed the presence of 43- to 54-kDa UT-B proteins. Immunolocalization studies showed that UT-B was mainly located on cell plasma membranes in epithelial layers of the bovine rumen. Ussing chamber measurements of ruminal transepithelial transport of (14)C-labeled urea indicated that urea flux was characteristically inhibited by phloretin. We conclude that bUT-B is expressed in the bovine rumen and may function to transport urea into the rumen as part of the ruminant urea nitrogen salvaging process.

Expression and distribution of monocarboxylate transporter 1 (MCT1) in the gastrointestinal tract of calves

In the present study the expression and distribution of monocarboxylate transporter 1 (MCT1) along the gastrointestinal tract (rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum and colon) of calves were investigated on both mRNA and protein levels. The expression of MCT1 protein and its distribution were determined by Western blotting and immunohistochemical staining, respectively by using antibody for MCT1. MCT1 protein was visualized as a 43-kDa band on immunoblots of the membrane proteins prepared from the various regions examined, and it was more highly expressed in forestomach and large intestine than in abomasum and small intestine. With the use of reverse transcriptase-polymerase chain reaction, mRNA encoding for MCT1 was demonstrated in the different tissues examined. The immunohistochemical study confirmed the Western blot findings and showed strong MCT1 immunopositive staining in the stratified squamous epithelia of the forestomach as well as the epithelial cells lining the digestive tract in the cecum, proximal colon, and distal colon. The results suggest that MCT1 may play a role in the transport of SCFA and their metabolites in the gastrointestinal tract of bovines.

Functional organization of the bovine rumen epithelium

The functional organization of the bovine rumen epithelium has been examined by electron and light microscopy combined with immunocytochemistry to define a transport model for this epithelium. Expression of connexin 43, an integral component of gap junctions, the tight-junction molecules claudin-1 and zonula occludens 1 (ZO-1), and the catalytic α-subunit of Na+-K+-ATPase was demonstrated by SDS-PAGE and Western blotting. From the lumen surface, four cell layers can be distinguished: the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale. Both claudin-1 and ZO-1 immunostaining showed plasma membrane staining, which was present at the stratum granulosum with decreasing intensity through the stratum spinosum to the stratum basale. The stratum corneum was negative for claudin-1 immunostaining. Transmission electron microscopy confirmed that occluding tight junctions were present at the stratum granulosum. Plasma membrane connexin 43 immunostaining was most intense at the stratum granulosum and decreased in intensity through stratum spinosum and stratum basale. There was intense immunostaining of the stratum basale for Na+-K+-ATPase, with weak staining of the stratum spinosum. Both the stratum granulosum and the stratum corneum were essentially negative. Stratum basale cells also displayed a high mitochondrial density relative to more apical cell layers. We conclude that epithelial barrier function may be attributed to the stratum granulosum and that cell-cell gap junctions allow diffusion to interconnect the barrier cell layer with the stratum basale where Na+-K+-ATPase is concentrated.

Effects of volatile fatty acid supply on their absorption and on water kinetics in the rumen of sheep sustained by intragastric infusions1

Three sheep fitted with a ruminal cannula and an abomasal catheter were used to study water kinetics and absorption of VFA infused continuously into the rumen. The effects of changing VFA concentrations in the rumen by shifting VFA infusion rates were investigated in an experiment with a 3 x 3 Latin square design. On experimental days, the animals received the basal infusion rate of VFA (271 mmol/h) during the first 2 h. Each animal then received VFA at a different rate (135, 394, or 511 mmol/h) for the next 7.5 h. Using soluble markers (polyethylene glycol and Cr-EDTA), ruminal volume, liquid outflow, apparent water absorption, and VFA absorption rates were estimated. There were no significant effects of VFA infusion rate on ruminal volume and water kinetics. As the VFA infusion rate was increased, VFA concentration and osmolality in the rumen were increased and pH was decreased. There was a biphasic response of liquid outflow to changes in the total VFA concentration in the rumen, as both variables increased together up to a total VFA concentration of 80.1 mM, whereas, beyond that concentration, liquid outflow remained stable at an average rate of 407 mL/h. There were significant linear (P = 0.003) and quadratic (P = 0.001) effects of VFA infusion rate on the VFA absorption rate, confirming that VFA absorption in the rumen is mainly a concentration-dependent process. The proportion of total VFA supplied that was absorbed in the rumen was 0.845 (0.822, 0.877, and 0.910 for acetate, propionate, and butyrate, respectively). The molar proportions of acetate, propionate, and butyrate absorbed were affected by the level of VFA infusion in the rumen, indicating that this level affected to a different extent the absorption of the different acids.

Transport of ketone bodies and lactate in the sheep ruminal epithelium by monocarboxylate transporter 1

Due to intensive intracellular metabolism of short-chain fatty acids, ruminal epithelial cells generate large amounts of D-beta-hydroxybutyric acid, acetoacetic acid, and lactic acid. These acids have to be extruded from the cytosol to avoid disturbances of intracellular pH (pH(i)). To evaluate acid extrusion, pH(i) was studied in cultured ruminal epithelial cells of sheep using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Extracellular addition of D-beta-hydroxybutyrate, acetoacetate, or lactate (20 mM) resulted in intracellular acidification. Vice versa, removing extracellular D-beta-hydroxybutyrate, acetoacetate, or lactate after preincubation with the respective monocarboxylate induced an increase of pH(i). Initial rate of pH(i) decrease as well as of pH(i) recovery was strongly inhibited by pCMBS (400 microM) and phloretin (20 microM). Both cultured cells and intact ruminal epithelium were tested for the possible presence of proton-linked monocarboxylate transporter (MCT) on both the mRNA and protein levels. With the use of RT-PCR, mRNA encoding for MCT1 isoform was demonstrated in cultured ruminal epithelial cells and the ruminal epithelium. Immunostaining with MCT1 antibodies intensively labeled cultured ruminal epithelial cells and cells located in the stratum basale of the ruminal epithelium. In conclusion, our data indicate that MCT1 is expressed in the stratum basale of the ruminal epithelium and may function as a main mechanism for removing ketone bodies and lactate together with H+ from the cytosol into the blood.