The rat model can be used to assess ileal protein digestibility rapidly and in first intention, but no standardised method exists. Our objective was to compare methods to assess protein digestibility, depending on collection site (ileum/caecum) and use of a non-absorbable marker. A meal containing either casein, gluten or pea protein and chromium oxide as non-absorbable marker was given to male Wistar rats and the entire digestive content was collected 6 h later. Total chromium recovery was incomplete and variable, depending on protein source. We observed no significant difference in digestibility between the methods for any of the protein sources tested. Although none of the methods tested is optimal, our results suggest that caecal digestibility can be used as a proxy of ileal digestibility in rats without using a non-absorbable marker. This simple method makes it possible to evaluate protein digestibility of new alternative protein sources for human consumption.

Postileal fermentation in the gastro intestinal tract of poultry is affected by the main raw materials used during feed formulation, for example cereal grains, rapeseed meal, soybean meal, lupin seeds. Since cereal grains are the main source of dietary non-starch polysaccharides, including the viscous water-soluble fraction, their quality determines the rate of postileal fermentation. The supplementation of poultry diets with selected enzymes, mostly xylanase andß-glucanase, suppresses fermentation in the upper gastro intestinal tract, and enhances the process in the caecum. Due to relatively high concentrations of raffinose family oligosaccharides in soybean meal, diets rich in that raw material may stimulate gut fermentation and decrease the growth performance of young birds. Rapeseed meal and lupin seeds, used as partial substitutes for soybean meal, affect fermentation processes in the gastrointestinal tract of poultry to a low degree, as compared with a soybean-based diet. Sunflower meal, even at low inclusion levels (14%), reduces the synthesis of caecal short chain fatty acids, probably due to an increase in lignified fibre in the diet.

Postileal fermentation in the gastrointestinal tract of poultry takes place as a result of the interaction between two components of the intestinal ecosystem: rapidly changing microbiota and digesta with different physicochemical properties. Short chain fatty acids, the major products of fermentation, act to stabilise microbiota composition and maintain gut health, and constitute an additional source of energy. Due to different mechanisms of action of probiotics, phytobiotics and prebiotics in the intestinal ecosystem, the quantities and proportions of the major products of fermentation are affected by the type of feed additives. Some phytobiotics, including alkaloids, exert antimicrobial effects and reduce short chain fatty acids concentrations in the caecum. Mannan-oligosaccharides, regarded as prebiotics, may prevent the adhesion of pathogenic bacteria (mostly E. coli and Salmonella) to the gut wall. Prebiotic oligosaccharides, in particular fructo-oligosaccharides and inulin, are used by beneficial bacteria of the genera Bifidobacterium and Lactobacillus, thus enhancing the synthesis of short chain fatty acids in the lower gastro intestinal tract of poultry, while low intestinal pH inhibits the growth of pathogenic bacteria.

The present study investigated the effects of fructo-oligosaccharides (FOS) on the bioavailability of Fe from ferric pyrophosphate (FP), a water-insoluble compound, in Fe-deficient anaemic rats that were subjected to a Hb repletion assay. Male Wistar rats (n 64) were fed adequate or low (8 mg/kg) Fe diets for 15 d followed by 1 or 2 weeks of Fe repletion with diets providing 35 mg Fe/kg as ferrous sulphate (FS), FP or FP that was mixed with 7·5 % FOS in the form of yacon flour or Raftilose P95 (RAF), a purified source of FOS. The effects of FOS were observed within the 1st week of the repletion period. Fe bioavailability was improved by FOS supplementation, as measured by Hb regeneration efficiency and hepatic Fe stores, which were more pronounced in the RAF group. Moreover, RAF supplementation resulted in a higher biological value relative to that of the FP group. FOS supplementation resulted in caecal enlargement, in addition to acidification and Fe species redistribution in the caecal contents relative to the control rats. These effects occurred concomitantly with decreased ferroportin (FPN)-1 expression in the caecal mucosa, which was similar in magnitude to that observed in the FS group. Caecum mucosal morphometry was influenced by FOS supplementation, whereas crypt fission and cell proliferation were highest in the caecum of the RAF group. These results reinforce the effects of FOS as Fe bioavailability enhancers in anaemic rats that are sustained by early changes in their caecal environment (decreased mucosal FPN-1 expression and increased Fe absorbability, crypt fission and cellularity).

The effect of high-grain (HG) feeding on caecal bacterial microbiota composition and fermentation and mucosa health is largely unknown. In the present study, ten male goats were randomly assigned to either a group fed a hay diet (0 % grain; n 5) or a group fed a HG diet (65 % grain; n 5) to characterise the changes in the composition of the bacterial community and mucosal morphology in the caecum. After 7 weeks of feeding, the HG diet decreased the caecal pH (P< 0·001) and increased (P< 0·001 to P< 0·004) the caecal digesta concentrations of total volatile fatty acids and lipopolysaccharide (LPS). Pyrosequencing of the 16S ribosomal RNA gene revealed that HG feeding increased (P= 0·001 to P= 0·009) the abundance of predominant genera Turicibacter and Clostridium in the caecal lumen and in the caecal mucosa and decreased (P< 0·001 to P< 0·009) the proportion of Bacteroides in the lumen and Mucispirillum in the mucosa compared with the hay diet. Furthermore, the HG diet-fed goats exhibited intense epithelial damage and up-regulation (P< 0·001 to P< 0·025) of the relative mRNA expression of IL-1β, IL-6, IL-12 and interferon-γ (IFN-γ) in the caecal mucosa. The correlation analysis revealed that alterations in caecal pH, LPS concentration and mucosa-associated microbiota abundance during HG feeding might partly contribute to local inflammation. Collectively, these results provide insight into the adaptive response of caecal bacterial populations to HG feeding in goats and reveal that the fermentable substrates that flow into the caecum may cause dramatic alterations in microbial compositions and play a significant role in caecal dysfunction.

The present 4-week study on growing Wistar rats was aimed at assessing the potential advantages of dietary supplementation with apple pomace containing both fibre and polyphenols, which enables nutritional exploitation of the physiological traits of both compounds. A total of twenty-four rats, assigned to the control (C), group fed with a diet supplemented with 14 % of processed apple pomace (A) and group fed with a diet supplemented with 15 % unprocessed apple pomace (AP) groups, were fed the following iso-fibrous diets: control, ethanol-extracted and unprocessed apple pomaces (low and high level of dietary polyphenols, i.e. 0·002 and 0·018 %, respectively). To measure the animal response, parameters describing the caecal fermentation, antioxidative status and lipoprotein profile of rats were assessed. Both dietary apple pomaces were found to significantly (P ≤ 0·05) decrease caecal pH and ammonia concentration, microbial β-glucuronidase activity as well as to increase caecal SCFA concentration in comparison to the control diet. The unprocessed pomace did not suppress caecal fermentation. Unlike the extracted one, the dietary apple pomace rich in polyphenols significantly (P ≤ 0·05 v. C group) increased erythrocyte superoxide dismutase activity and serum antioxidant capacity of lipid-soluble substances and significantly (P ≤ 0·05 v. C group) decreased amounts of thiobarbituric acid-reactive substances in liver tissue. Moreover, the 4-week administration of the AP diet to rats evoked a significant decrease in serum glucose concentration (P ≤ 0·05 v. C and A groups). In conclusion, the results demonstrated that the polyphenol-rich fibre complexes from apple pomace exerted positive effects on gastrointestinal physiology and antioxidant status of rats.

The aim of this 28 d experiment was to examine the physiological response of growing rats to a dietary combination of prebiotic chicory fructans, with polyphenols originating from different parts of the chicory plant, i.e. roots, root peels, seeds and leaves. A total of forty rats were assigned to groups fed the following diets characterised by a similar content of oligofructose and inulin: control, with 10 % of a root extract (a low level of dietary polyphenols, 0·05 %), with 6·5 % of a root peel extract (a medium level of dietary polyphenols, 0·107 %), with a combination of 8 % of a peel extract and 0·8 % of a seed extract (a high level of dietary polyphenols, 0·208 %) and with 2·5 % of a leaf extract (a medium level of dietary polyphenols, 0·106 %, with chicoric acid constituting half of them). Chicory seeds are the richest source of polyphenols, especially abundant in dicaffeoylquinic acids. When applied as a dietary supplement, the mixture of monocaffeoylquinic and dicaffeoylquinic acids, from the extracts made of roots, root peels and seeds, elicited more favourable changes in parameters of the antioxidative status of the body and in the activity of bacterial β-glucuronidase in the faeces and caecal digesta. In turn, the extract from chicory leaves, containing considerable quantities of chicoric acid and polyphenolic glycosides, apart from chlorogenic acids, also triggered desirable changes in the lipid profile of the blood serum. The high concentration of polyphenols in the extracts examined enables their application as dietary supplements to be administered in low doses.

Colonic fermentation products, SCFA, have various effects on colonic functions. Here, we found that physiological concentrations of SCFA immediately promote epithelial barrier function in the large intestine. Solutions of mixed and individual SCFA were applied to the caecal walls mounted on Ussing-type chambers. Transepithelial electrical resistance (TER) increased rapidly and reached a peak 35 % higher than that in the control specimen within 10 min post application of the SCFA mixture (80 acetate, 40 propionate, 20 butyrate (mmol/l)). The Lucifer yellow permeability, a paracellular transport marker, was dose-dependently reduced by the mixed SCFA, acetate and propionate solutions. Inhibition of monocarboxylate transporter-1 did not influence the increase in TER with acetate; however, lowering the pH (from 7·5 to 5·5) clearly enhanced the effect of acetate. Non-metabolizable, bromo and chloro derivatives of SCFA also increased TER. These results suggest that passive diffusion of SCFA is dominant and the metabolism of SCFA is not required for the promotive effect of SCFA on barrier function. We also observed that individual SCFA dose-dependently increased TER in T84 and Caco-2 cells, which indicates that SCFA directly stimulate epithelial cells. Depletion of membrane cholesterol and inhibitors of phosphatidylinositol-3 kinase and Gq protein attenuated the acetate-mediated promotive effect. Finally, we found that the mucosal application of the SCFA mixture dose-dependently suppressed [3H] mannitol transport from the caecal lumen to the mesenteric blood in the anaesthetized rats. We conclude that physiological concentrations of SCFA immediately enhance barrier function of the colonic epithelium through cholesterol-rich microdomain in the plasma membrane.

Response to an experimental infection with an enteropathogenic E. coli O103 strain (EPEC) was assessed in growing rabbits given a high or a low dietary fibre diet (200 and 120 g acid-detergent fibre per kg respectively for high ‘HF’ or low ‘LF’ fibre diet). The two experimental diets, differing in fibre level but not fibre quality, were given ad libitum from 21 days of age to two groups of 12 litters of nine pups, weaned at 28 days (trial 1) and caged collectively. At 42 days of age, the two groups were divided in two subgroups (i.e. four groups of 18 animals), inoculated or not with an EPEC O103 strain. Two further groups of 48 rabbits (trial 2) were given LF and HF diets from 28 days (weaning) to 70 days, and were individually housed to control precisely the food intake. Reducing the fibre level led to a lower post-weaning food intake (64 v. 85 g/days in the period from 28 to 42 days of age, P < 0·001) and digestible energy intake (0·75 v.. 0·86 MJ/day, P < 0·001), causing a lower growth (proportionately 0·088 lower, P < 0·001). At 42 days of age, only 17% of rabbits had a detectable caecal saprophyte E. coli flora (over 102 colony-forming units (CFU) per g, trial 1). Inoculating 6-week-old rabbits with EPEC led to moderate levels of mortality (26%). Health risk index (mortality + morbidity) was numerically higher in LF compared with HF groups (P = 0·12). The acute phase of the colibacillosis was between 3 and 10 days post inoculation. From days 7 to 14 post inoculation, a significantly higher frequency of rabbits having a high faecal excretion of E. coli (> 105 CFU per g) was found in LF than in HF rabbits (respectively 65 v. 26·7%, P = 0·04). The caecal pectinolytic flora reached 108 CFU per g at 42 and 65 days of age, and was not affected by diet or EPEC challenge. In 42-day-old rabbits the caecal volatile fatty acid concentration was higher in HF than in LF groups (respectively 79 v. 60 mmol/l, P < 0·05), while the caecal pH was slightly lower (respectively 5·93 v. 6·09, P < 0·01). At 65 days of age, rabbits resistant to the inoculation showed a similar fermentation pattern and fibrolytic flora level to non-inoculated animals. Caecal ammonia level was not affected either by age, diet or E. coli challenge (mean = 12·1 mmol/l). From these results, we conclude that a high fibre intake improved the resistance of the growing rabbit to a specific enteropathy, in association with a higher caecal fermentative activity and lower caecal pH.

Three experiments were conducted to investigate the effect of bag incubation sequence on the degradation of food components in situ in the caecum of mature, caecally fistulated Welsh-cross pony geldings (mean live weight 278 kg) offered hay ad libitum. In experiment 1 a fibre-based commercial horse concentrate was incubated in situ using a forward (3, 5, 16, 8, 24, 48 h) or reverse (48, 24, 8, 16, 5, 3 h) incubation sequence. Dry matter (DM), crude protein (CP), neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) degradation coefficients and calculated effective degradability (ED) values were determined. In experiment 2 unmolassed sugar-beet pulp (USBP), hay cubes (HC), soya hulls (SH) and a 2: 1 mixture of oat hulls: naked oats (OHNO) were incubated in situ as for experiment 1. In experiment 3 unprocessed barley (UB), micronized barley (MB), extruded barley (EB) and dehydrated grass (DHG) were incubated in situ according to slightly different forward or reverse incubation sequences of (2, 4, 6, 12, 8, 24, 48 h) and (48, 24, 8, 4, 12, 6, 2 h) respectively. In experiments 2 and 3 only DM degradation parameters were studied.

Of the three starch-based foods studied in experiment 3 (UB, MB and EB), incubation sequence did not significantly P > 0·05) affect any of the degradation parameters examined. Conversely however, of the six fibre-based foods which were examined across the three experiments, incubation sequence did significantly P < 0·05) affect in situ degradation parameters in the commercial horse concentrate in experiment 1, the SH food in experiment 2 and the DHG food in experiment 3. Depending on the food or food constituent studied (i.e. DM, CP, NDF or ADF) degradation coefficients a, b, c and a + b along with ED values calculated at fractional outflow rates of 0·05 and 0·025 could all be statistically different CP < 0·05) according to whether a forward or reverse incubation sequence was used. It is postulated that this effect is related to the basic digestive physiology of the equine caecum which is small, digesta passage rate through it is fast and digesta volumes can vary considerably. These factors may interact to create a considerable degree of non-uniformity within the caecal digesta pool in which in situ bags are incubated. Consequently, it is recommended that in future in situ experiments in the equine hindgut, animals are offered ad libitum diets in an attempt to minimize variation within the caecum. It is also recommended that in situ experimental protocols incorporate more than one incubation sequence when the degradation parameters of fibrous foods are studied in equids.

In Strongyloides ratti-infected rats, 2 peaks of egg excretion were observed; a large one with maximum egg production on days 7–8 of infection and a small more inconspicuous one around day 25. The second peak, which had been ignored in most studies, was produced by adults in the caecum and the colon. The adults were larger in length and had more embryonated eggs in the uterus compared with adults in the small intestine at day 25 post-infection. It is suggested that parasitic adults once expelled from the small intestine resettle and recover in the large intestine. Filter paper faecal culture carried out for 9 days at different days post-infection revealed that the total number of infective larvae that developed during the second peak was twice the number that developed during the first peak, despite the fact that total egg output during the second peak was less than one twentieth of the first peak. The results suggest that the small second peak was as important as the first one in the transmission of S. ratti.

The energetic contribution from, and effects on the gastrointestinal tract of, indigestible oligosaccharides in growing rats were compared with those of sucrose (S). S and two types of oligosaccharides, fructo-oligosaccharide (Fru) and 6'-galacto-oligosaccharide (Gal) were added to a basal diet at a level of 100 g/kg. The basal diet was given either ad libitum (group B) or at a level approximately 90% of the ad libitum intakes of the Fru and Gal groups (group BR). During a 50 d feeding period, feed intake, digestibilities of nutrients, and digesta retention times using liquid (Co-EDTA) and particulate (Cr-cell-wall constituents) markers were measured. The carcass and the contents of the stomach and caecum were sampled on the last day of the experimental period. There was no significant difference in feed intake between groups other than BR. Addition of Fru and Gal to the basal diet resulted in increased crude ash digestibility and decreased crude protein and fat digestibilities. Mean retention times of digesta markers were increased by addition of Fru and Gal to the diet, and this was associated with enlargement of the caecum. Concentrations and amounts of total organic acids in the caecum were higher in groups Fru and Gal than the other groups. The amount of energy accumulated in the carcass of rats in the Gal group was significantly (P < 0.05) lower than that of rats fed on S but not Fru. Contributions to energy accumulation tended to be different between Fru and Gal; these were associated with differences in composition of caecal organic acids and of fatty acids in body fat.

Effects of feeding soluble dietary fibre on apparent Ca absorption and the contribution of the caecum to Ca absorption were examined in five-sixths nephrectomized (NPX)and normal rats with or without caecectomy in four experiments. It is known that Ca absorption is lowered by renal failure. In the first experiment the amounts of femur Ca increased linearly with increasing dietary Ca up to 3·0 g Ca/kg diet in intact rats. Partial nephrectomy decreased apparent Ca absorption in rats fed on diets containing 30 and 4·5 g Ca/kg diet. In the NPX groups, Ca absorption in rats fed on the diet containing guar-gum hydrolysate (GGH; 50 g/kg diet; 3·0 g Ca/kg diet) was significantly higher than that in rats fed on a fibre-free diet, and the increase in Ca absorption with GGH feeding was completely abolished by caecectomy. Also, ingestion of GGH increased Ca absorption in normal rats, but not in normal, caecectomized rats. Mg absorption was also increased with GGH feeding and was decreased with caecaectomyin NPX and normal rats. In experiments which used caecectomized rats, coprophagy wasprevented with an anal cup to avoid re-ingestion of faecal Ca. We conclude that ingestion of the soluble dietary fibre, GGH, increased apparent Ca absorption in NPX and non-NPX rats, and the caecum was responsible for these increases in Ca absorption.

The effect of fermentation on colonic absorption of Ca and Mg was investigated in 8-week-old rats adapted to diets containing either digestible wheat starch (DS diets) or including resistant starch, i.e. 350 g raw potato starch/kg (RS diets). The dietary Ca level of the DS and RS diets was 2·5 or 7·5 g/kg. RS diets resulted in enlargements of the caecum together with hypertrophy of the caecal wall. Acidification of the caecal contents by mictobial fermentation of RS was influenced by the dietary Ca level. Very acidic pH conditions and relatively low concentrations of short-chain fatty acids, in the presence of lactic acid fermentation, were observed with the 2·5 g Ca/kg level. Rats fed on RS diets had a bhigher pencentage of soluble Ca (and inorganic phosphate) in the caecum, particularly of rats adapted to the high Ca level. As a result of the hypertrophy of the caecal wall and of an elevated concentration of soluble Cas, the caecal absorption of Ca was 5-6 fold higher in the RS groups than in the DS groups. The difference between dietary intakle and faecal excretion (DI-FE) of Ca was higher in rats fed on RS diets than in those fed on DS diets, when the dietary Ca level was 2·5 g/kg. With the higher Ca intake the elevated rate of Ca absorption from the caecum in RS-fed rats was not paralleled by an enhanced DI-EE difference: this suggests a shift of the Ca absorption towards the large intestine. Feeding Rs diets also enhanced Mg caecal absorption, resulting in the substatntially higher DI-FE difference for Mg, especially with the 2·5 g Ca/kg diets, because a high Ca intake tends to inhibit Mg absorption. The present findings support the view that the large intestine may represent a major site of Ca (and Mg) absorption when acidic fermentations take place. This process could improve the digestive Ca balance when the dietary Ca supply is low; when the Ca supply is affluent, it rather shits Ca absorption towards a more distal site fo the digestive tract.

Fermentable energy in insoluble dietary fibre (DF) sources was evaluated by in vivo and in vitro methods using rats. Test diets contained 50 and 100 g maize husk or organic-acid-treated maize husk/kg diet. Soluble fractions were removed from both the DF sources by washing. The acid treatment increased digestibility by a microbial hemicellulase from 12.7% to 32.6%. The fermentabiliry of DF was evaluated by measurement of the production rate of short-chain fatty acids (SCFA) in a short-term in vitro incubation of the caecal contents of rats fed on test diets for 22 d. The production rates of the major SCFA, acetic, propionic and butyric acids, were increased by feeding both DF sources, and these production rates in the acid-treated DF group were significantly higher than those in the untreated DF group. The production rate of a minor SCFA, isovaleric acid, was decreased by feeding both diets. The production rate of total SCFA in rats given the acid-treated maize husk was 32.6% higher than that in rats given the untreated maize husk. The fermentable energy in DF was estimated in vivo by subtracting the faecal excretion of DF energy from ingested DF energy. The fermentable energy in DF was increased by the acid treatment (32·5% in maize husk and 63.4% in acid-treated maize husk), which agreed with the SCFA production rate predicted in the caecum. These results indicate that a short-term incubation of caecal contents is a useful method for evaluation of the fermentability of DF sources, and that acid treatment can increase the fermentability of an insoluble DF source.