ß-Glucan-Induced Immuno-Modulation: A Role for the Intestinal Microbiota and Short-Chain Fatty Acids in Common Carp.

Dietary supplementation of fish with ß-glucans has been commonly associated with immunomodulation and generally accepted as beneficial for fish health. However, to date the exact mechanisms of immunomodulation by ß-glucan supplementation in fish have remained elusive. In mammals, a clear relation between high-fibre diets, such as those including ß-glucans, and diet-induced immunomodulation via intestinal microbiota and associated metabolites has been observed. In this study, first we describe by 16S rRNA sequencing the active naive microbiota of common carp intestine. Based on the abundance of the genus Bacteroides, well known for their capacity to degrade and ferment carbohydrates, we hypothesize that common carp intestinal microbiota could ferment dietary ß-glucans. Indeed, two different ß-glucan preparations (curdlan and MacroGard®) were both fermented in vitro, albeit with distinct fermentation dynamics and distinct production of short-chain fatty acids (SCFA). Second, we describe the potential immunomodulatory effects of the three dominant SCFAs (acetate, butyrate, and propionate) on head kidney leukocytes, showing effects on both nitric oxide production and expression of several cytokines (il-1b, il-6, tnfα, and il-10) in vitro. Interestingly, we also observed a regulation of expression of several gpr40L genes, which were recently described as putative SCFA receptors. Third, we describe how a single in vivo oral gavage of carp with MacroGard® modulated simultaneously, the expression of several pro-inflammatory genes (il-1b, il-6, tnfα), type I IFN-associated genes (tlr3.1, mx3), and three specific gpr40L genes. The in vivo observations provide indirect support to our in vitro data and the possible role of SCFAs in ß-glucan-induced immunomodulation. We discuss how ß-glucan-induced immunomodulatory effects can be explained, at least in part, by fermentation of MacroGard® by specific bacteria, part of the naive microbiota of common carp intestine, and how a subsequent production of SFCAs could possibly explain immunomodulation by ß-glucan via SCFA receptors present on leukocytes.

Evaluation of equine rectal inoculum as representative of the microbial activities within the horse hindgut using a fully automated in vitro gas production technique system.

The in vitro gas production technique (IVGPT) has been a valuable tool in ruminant nutrition research for decades and has more recently been used in horse nutrition studies to investigate fermentation activities of the equine hindgut though primarily using feces as inoculum. This study was conducted to evaluate the use of equine rectal content in the IVGPT system as a viable inoculum that can be considered representative of the activities throughout the equine hindgut. Additionally, the study was conducted to measure the effects on fermentation kinetics and end-product production using inoculum from horses fed supplemental levels of coated sodium butyrate in an IVGPT system. Eight warmblood horses were fed a diet consisting of haylage (1% DM intake based on ideal body weight [BW]) and a mash concentrate formulated to provide 2.5 g nonstructural carbohydrate (NSC)/kg BW per meal. The diet was intended to create a NSC challenge to the microbial populations of the hindgut. The horses were randomly assigned to treatment or control group and after a 1-wk diet-adaptation period, the treatment group received 0.4 g/kg BW per day of a coated sodium butyrate supplement, while the control group received a placebo (coating only). After a 3-wk treatment period, the animals were sacrificed and digesta from the cecum, left ventral colon, right dorsal colon, and the rectum were collected within 30 min postmortem and used as inocula for the IVGPT trial. Haylage and concentrates fed to the test animals were also used as substrates in vitro. Sodium butyrate supplementation was not significant for gas production parameters or VFA measured suggesting no effect of sodium butyrate supplementation on the extent or kinetics of gas production or microbial end-product production (P ≥ 0.073). Differences in inocula were significant for organic matter corrected cumulative gas production (P = 0.0001), asymptotic gas production of the second phase (A2) (P < 0.0001); and maximal rate of OM degradation of the second phase (Rmax2) (P = 0.002). Inocula had a significant effect on total VFA (P = 0.0002), butyrate (Bu) (P = 0.015), branched chain fatty acids (P < 0.0001), pH (P < 0.0001), and ammonia (NH3) (P = 0.0024). In conclusion, based on observed results from this study, total tract digestibility may be overestimated if using rectal content inoculum to evaluate forage-based feeds in an IVGPT system.

Isolipidic replacement of krabok oil by whole krabok seed reduces in vitro methanogenesis, but negatively affects fermentation.

The background of the current in vitro study involves the issue of methane (CH4 ) production inherent to rumen fermentation. One of the dietary strategies to reduce enteric CH4 production by ruminants involves the supplementation of medium-chain fatty acids in diets. As such, oils containing high amounts of MCFA, such as coconut, palm kernel and krabok oil, are of much interest to formulate energy efficient and environmentally friendly rations for ruminants. Krabok oil (KO) reduces methanogenesis, but the appropriate inclusion level of dietary KO is unclear. We therefore investigated the dose-response relationship between krabok oil and CH4 production. In practice, the use of whole krabok seed (WKS), instead of KO, is easier, but the efficacy of WKS to inhibit methanogenesis was hitherto unknown. Thus, we also investigated whether WKS provides an alternative tool to inhibit CH4 production. The experimental substrates contained either KO, WKS, the residue of WKS after fat extraction residue (FER) or FER + KO. Appropriate amounts of WKS or its derivatives were added to a basal substrate so as to attain either a low, medium or high content of KO, that is, 37-46, 90-94 and 146-153 g/kg dry matter respectively. The experimental substrates were formulated to keep the amounts of incubated fat-free OM, crude protein, neutral detergent fibre and acid detergent fibre constant in order to avoid biased results through potential differences in fermentability between WKS and its derivatives, and the basal substrate. The latter resembled the ingredient composition of a total mixed ration commonly used in Thai dairy cows. Fully automated gas production (GP) equipment was used to measure gas- and CH4 production. Irrespective of the type of substrate (p ≥ .115), both the absolute (ml/g fat-free OM) and relative (% of total GP) CH4 production was reduced at the highest inclusion level of WKS or its derivatives (p ≤ .019). Total GP (ml/g fat-free OM), however, was reduced after incubation of FER, FER + KO, and WKS, but not KO, at the highest inclusion level of the respective substrates (p = .019). Volatile fatty acids were likewise affected (p ≤ .001). Krabok oil can inhibit CH4 production but only when the dietary KO content is at least 9.4% (DM). Supplementation of KO in the form of WKS, however, is considered not opportune because the fat extracted residue of WKS is poorly degraded during fermentation.

Condensed Tannins in the Gastrointestinal Tract of Cattle after Sainfoin (Onobrychis viciifolia) Intake and Their Possible Relationship with Anthelmintic Effects.

Condensed tannins' (CTs) fate along the digestive tract of ruminants may account for the variable efficacy of CTs against gastrointestinal nematodes. We analyzed CTs in the digesta of cattle fed sainfoin. With the acetone-butanol-HCl assay, the total CTs concentrations in the digesta were close to those in the diets (6.3 and 1.5% of DM in experiments 1 and 2, respectively); thus, CTs remained potentially largely undegraded/unabsorbed. With the thiolysis assay, CTs concentration was much higher in the abomasum (2.3% of DM; expt 1) compared with the rumen and intestines, along with higher mean size and prodelphinidins percentage, corroborating CTs efficacy reported only against Ostertagia ostertagi in the abomasum. In expt 2, the dietary levels of CTs were probably too low to demonstrate anthelmintic effects in the rumen. Overall, the level of CTs accessible to thiolysis is favored under the acidic conditions of the abomasum, which seems critical for anthelmintic activity.

Repeated measurements of in vitro fermentation of fibre-rich substrates using large intestinal microbiota of sows.

BACKGROUND: Fibrous ingredients for pig diets can be characterized by in vitro fermentation. In vitro fermentation methods often use a one-time measurement of gas production during the incubation of test substrates with one faecal inoculum. The representativeness of this approach can be questioned as measuring time and number of animals from which inoculum originates may influence fermentation results. An in vitro fermentation trial was conducted incubating three fibrous substrates with three inocula in five replicates (different fermentation runs) to test the influence of run and origin of inocula. RESULTS: Total gas production and maximal rate of gas production differed (P < 0.05) between fermentation runs, but less than substrates (P < 0.01). The ranking order between substrates remained similar for each run. Fermentation of cellulose led to higher coefficients of variation between inocula compared to the fast fermentable substrates oligofructose and soy pectin. Differences ranged from 2% for total gas production up to 25% for maximal rate of gas production. CONCLUSION: One fermentation run can provide representative results for substrate ranking. Using multiple inocula mixed from four faecal samples each leads to high coefficients of variation for slow fermentable substrates like cellulose. Future studies should examine the optimal number of animals for inocula preparation to decrease variation.