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Male rats were fed on either a non-purified rodent diet (JS) or cholesterol-free purified diets containing wheat bran (WB) or oat bran (OB). Some animals were allowed normal access to their faeces for coprophagy (coprophagy+), while in others coprophagy was prevented by placement of a plastic cup over the anus (coprophagy-). Direct ingestion of faeces from the anus was observed in the former groups. Food intake was unaffected by diet or coprophagy status and body weight gain was unchanged with OB- and JS- but was significantly lower with WB-. Plasma cholesterol was highest with WB and equally lower with OB and JS and was unaffected by coprophagy status. Plasma triacylglycerols were highest with OB and were unaffected by coprophagy status. Caecal digesta mass was highest with JS, intermediate with OB and lowest with WB. Digesta mass was unaffected by coprophagy status with WB and JS but was higher with OB-. Digesta moisture content was lowest with WB+ but highest with WB-. Digesta volatile fatty acid (VFA) concentrations were similarly lower with OB+ and OB-, but were significantly lower with JS- and WB- than in the corresponding coprophagy+ group. In all groups digesta butyrate concentrations were reduced by coprophagy prevention. Pools of total VFA, acetate and butyrate in the digesta were highest with JS. Pools of total VFA in digesta were highest with JS+, OB+ and OB- and lowest with WB+ and WB-. The propionate pool was highest with OB-, intermediate with OB+, and equally low in all other groups. The pool of butyrate was highest with JS+ and lowest with OB-.(ABSTRACT TRUNCATED AT 250 WORDS)

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 degrees 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 degrees 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.

1. The abilities of cattle, sheep, goats, equines and rabbits to digest mature timothy (Phleum pratense) hay were compared. Apparent digestibilities were partitioned into true digestibility, metabolic faecal output (MFO) and fibre digestibility. The aid of the study was to determine the relative effects of fermentation site (among groups) and of body-weight (within groups) on the efficiency of digestion. 2. The ruminants were superior to equines, which were in turn superior to rabbits, in digesting fibre-components of the hay. A large individual variation in digestibility was noted only for the equines. Increasing body-weight was associated with higher digestibility in ruminants, but no such trends were seen in the non-ruminants. 3. The MFO expressed as a proportion of dry matter intake gave similar values for all groups (0.085-0.118). As a proportion of available microbial substrate originating from the feed, the values were found to be 0.167 for the ruminant, 0.425 for the equines and 2.13 for the rabbits. The value for the rabbits shows that their lower tract microflora must obtain energy from non-fibre components of the feed. No appreciable digestion of the generated microbes by the host was suggested by the values obtained for the equines.