Twenty-four finishing pigs (twelve Iberian and twelve Landrace) were used in a growing and slaughtering experiment. Animals were fed two diets differing in their ingredients, maize (diet C) or sorghum–acorn (diet A). At an average weight of 107·0 kg pigs were slaughtered and hindgut digesta sampled to study the effect of breed and diet on large bowel fermentation. Flows of digesta to the hindgut compartment were estimated based on an indigestible flow marker (Cr2O3) and were higher in Iberian than in Landrace pigs (P<0·001), and higher in animals fed diet A than diet C (P=0·07). The higher flows in Iberian pigs were mainly associated with a higher voluntary feed intake (3·50 v. 2·70 kg/d, P<0·01) and lower ileal digestibility of NSP (−12·8 v. 47·8, P<0·01). Differences between diets were mainly associated with a lower ileal digestibility of starch from diet A (89·2 v. 96·9%, P=0·06), although no differences in the resistant starch content were observed in vitro. Fermentation of different carbohydrates through the large bowel showed that NSP-glucose had lower digestibility in Iberian than in Landrace pigs (62·5 v. 94·2%, P<0·001), but no differences were observed in starch, or other NSP-fibre fractions (arabinose, xylose and galactose). The type and amount of carbohydrates reaching the large bowel were related to the diet but also to breed, and promoted differences in the fermentative activity associated with different volatile fatty acid patterns and changes in microbial enzymic activity.

The present experiment was designed to test the hypothesis that ageing modifies the gastrointestinal responses to a change in diet composition. Rats of the Wag/Rij strain, either young adult (4 months of age) or elderly (27 months of age), were given a basal semi-purified diet or a diet of similar major nutrient composition containing 500 g oatmeal/kg for 17–18 d. Elderly rats digested the dry matter (DM) and organic matter (OM) of both diets less well than did their young adult counterparts, with more of this digestion occurring in the distal intestine. The greater flow of OM to the caecum of oats-fed animals was accompanied by significant reductions in caecal pH and increases in caecal total short-chain fatty acids (SCFA) concentration which appeared to be independent of age. However, young adults responded to feeding on oats by showing a much larger increase in the molar proportion of butyrate (332%) than did elderly animals (79%). Elderly rats had longer duodenal villi than did young adults but effects of age or diet were not detectable at other sites. With both age-groups oats consumption was associated with significant stimulation of crypt cell proliferation rate (CCPR) in the small intestine and caecum, but for the colon there was a significant reduction in CCPR with oats feeding. A reduced ability of the aged large bowel (LB) to produce butyrate may contribute to the prevelance of LB disorders in the elderly.

To obtain quantitative information on the digestibility of the non-starch polysaccharides (NSP) fraction of white and wholemeal breads, rats were fed on diets in which freeze-dried bread (white, wholemeal or mixtures of the two) provided all the complex carbohydrates. In a second experiment the possibility that dietary fat concentration might influence NSP digestibility was tested by feeding diets containing 30 or 170 g maize oil/kg and either white or wholemeal bread. Multiple linear regression analysis provided little evidence of associative effects of dietary components on NSP digestibility and in the two experiments digestibilities of NSP for white and wholemeal breads were 0·77–0·82 and 0·47–0·52 respectively. Xylose- and arabinose-containing polymers were better digested than was cellulose for both breads. Replacing white by wholemeal bread markedly increased the molar proportion of butyrate in caecal volatile fatty acids at the expense of acetate. This was associated with greater flows of organic matter to the large bowel (LB) and a reduction in caecal transit time (Expt 2). There was little detectable ettect of dietary maize oil concentration on NSP digestibility or on LB fermentation. All breads contained some starch resistant to pancreatic α-amylase (EC 3.2.1.1) without previous treatment with dimethyl sulphoxide. The digestibility of this starch fraction was not significantly different from 1·0 for all diets except that containing wholemeal bread and the higher maize oil concentration where the apparent digestibility was 0·89.

The digestion of non-starch polysaccharides (NSP) and of resistant starch (RS) by rats fed on wholemeal-bread-based diets containing 0-450 g cooked, freeze-dried haricot beans (Phaseolus vulgavis)/kg diet was measured over the final 14 d of a 21 d feeding experiment. The bread and beans provided all the dietary polysaccharide. RS could not be detected consistently in faeces and it was assumed that this fraction was entirely fermented in the large bowel (LB). NSP digestibilities were 0.56 and 0.86 for wholemeal bread and beans respectively with no evidence that the dietary presence of beans affected digestibility of bread NSP. Bean non-cellulosic polysaccharides were highly digestible with values of 0.98, 0.88 and 0.99 for arabinose, xylose and uronic acids components respectively. There were large increases in organic matter flow to the LB when beans were fed which was associated with marked caecal hypertrophy and alterations in caecal volatile fatty acids (VFA) pattern. Calculated VFA absorption from the LB was 5-fold higher with the highest level of beans and this was reflected in higher concentrations of VFA in portal and heart blood.

Rats were fed on four semi-purified diets in which raw or cooked peas (Pisum sativum var. Sentinel) provided 250 or 500 g/kg diet. Pressure-cooking of peas followed by rapid freezing and freeze-drying increased the proportion of starch resistant to α-amylase (EC 3.2.1.1) without previous treatment with dimethyl sulphoxide. There were only minor effects of cooking on the digestibilities of non-starch polysaccharides and their constituent sugars. With the higher dietary pea concentration there were marked increases in the flow of organic matter to, and fermentation in, the large bowel. These increases were associated with significant increases in colonic tissue and contents weights, and in colonic transit time. Both cooking and dietary pea inclusion rate altered the pattern of volatile fatty acids in caecal contents and in portal blood.

Four diets were prepared in which cooked potatoes provided approximately 0.8 of the dry matter (DM) and all the polysaccharides. The potatoes were either boiled conventionally (unprocessed) or prepared by rehydrating a commercial ‘instant’ potato product with boiling water. The diets were fed to rats (six per diet) immediately after preparation or after storage at 4° for 48 h and observations made on site and extent of digestion and large bowel (LB) fermentation. All diets were equally well digested (overall means 0.95 and 0.96 for DM and organic matter (OM) respectively) with a significant proportion of this digestion occurring in the LB. More OM flowed to the LB with the ‘instant’ (0.18 of intake) than with the unprocessed potato diets (0.13 of intake) and was associated with markedly different fermentation patterns. When compared with rats fed on the unprocessed potato diets, those given ‘instant’ potatoes had smaller caecums with much shorter transit times, lower caecal pH, higher total volatile fatty acid (VFA) concentrations and a greater molar proportion of butyrate in these VFA. Storage of the diets for 48 h at 4° had relatively smaller effects on these variables. Possible mechanisms for the observed effects and implications for tissue metabolism and health are discussed. In addition, a simple and apparently novel method for quantifying coprophagy is proposed.

The digestion of non-starch polysaccharides (NSP) was studied in rats given semi-purified diets containing 0-500 g raw peas (Pisum sativum)/kg. NSP were equally well digested at all inclusion levels with digestibilities for individual constituents ranging from 0.58 for xylans to 0.99 for arabinose-containing polymers with a total NSP digestibility of 0.79. Increasing the dietary pea inclusion rate increased the amount of substrate flowing to the large bowel (LB) and this was associated with marked increases in caecal tissue and contents masses, a reduction in caecal transit time from 0.88 to 0.43 d and a threefold increase in faecal bacterial biomass output. Caecal pH fell as did the molar proportions of acetate, isobutyrate, isovalerate and valerate whilst butyrate increased when peas were included in the diet. Possible mechanisms for these fermentation end-product changes are discussed. Pea inclusion in the diet was associated with increased volatile fatty acid and 3-hydroxy butyrate concentrations in portal and heart blood. It was concluded that peas are a rich source of fermentable polysaccharides which produce a LB fermentation pattern of potential health benefit.