Dietary fibre and the importance of the gut microbiota in feline nutrition : a review

Domestic cats are obligate carnivores and in this light hindgut fermentation has been considered unimportant in this species. However, a diverse microbiota has been found in the small and large intestines of domestic cats. Additionally, in vitro and in vivo studies support the hypothesis that microbial fermentation is significant in felines with potential benefits to the host. Results on microbiota composition and microbial counts in different regions of the feline gastrointestinal tract are compiled, including a description of modulating host and technical factors. Additionally, the effects of dietary fibre supplementation on the microbiota composition are described. In a second section, in vitro studies, using inocula from fresh feline faeces and focusing on the fermentation characteristics of diverse plant substrates, are described. In vivo studies have investigated the effects of dietary fibre on a broad range of physiological outcomes. Results of this research, together with studies on effects of plant fibre on colonic morphology and function, protein and carbohydrate metabolism, and the effects of plant fibre on disease conditions that require a decrease in dietary protein intake, are shown in a third section of the present review. Conclusively, for fructans and beet pulp, for example, diverse beneficial effects have been demonstrated in the domestic cat. Both dietary fibre sources are regularly used in the pet food industry. More research is warranted to reveal the potential benefits of other fibre sources that can be used on a large scale in feline diets for healthy and diseased cats

Fermentable soluble fibres spare amino acids in healthy dogs fed a low-protein diet

Background: Research in cats has shown that increased fermentation-derived propionic acid and its metabolites can be used as alternative substrates for gluconeogenesis, thus sparing amino acids for other purposes. This amino acid sparing effect could be of particular interest in patients with kidney or liver disease, where this could reduce the kidneys'/liver's burden of N-waste removal. Since dogs are known to have a different metabolism than the obligatory carnivorous cat, the main objective of this study was to assess the possibility of altering amino acid metabolism through intestinal fermentation in healthy dogs. This was studied by supplementing a low-protein diet with fermentable fibres, hereby providing an initial model for future studies in dogs suffering from renal/liver disease. Results: Eight healthy dogs were randomly assigned to one of two treatment groups: sugar beet pulp and guar gum mix (SF: soluble fibre, estimated to mainly stimulate propionic acid production) or cellulose (IF: insoluble fibre). Treatments were incorporated into a low-protein (17 %) extruded dry diet in amounts to obtain similar total dietary fibre (TDF) contents for both diets (9.4 % and 8.2 % for the SF and IF diet, respectively) and were tested in a 4-week crossover feeding trial. Apparent faecal nitrogen digestibility and post-prandial fermentation metabolites in faeces and plasma were evaluated. Dogs fed the SF diet showed significantly higher faecal excretion of acetic and propionic acid, resulting in a higher total SCFA excretion compared to IF. SF affected the three to six-hour postprandial plasma acylcarnitine profile by significantly increasing AUC of acetyl-, propionyl-, butyryl- + isobutyryl-, 3-OH-butyryl-, 3-OH-isovaleryl- and malonyl-L-carnitine. Moreover, the amino acid plasma profile at that time was modified as leucine + isoleucine concentrations were significantly increased by SF, and a similar trend for phenylalanine and tyrosine's AUC was found. Conclusion: These results indicate that guar gum and sugar beet pulp supplementation diminishes postprandial use of amino acids favoring instead the use of short-chain fatty acids as substrate for the tricarboxylic acid (TCA) cycle. Further research is warranted to investigate the amino acid sparing effect of fermentable fibres in dogs with kidney/liver disease

Effect of guar gum on in vivo fermentation kinetics and end product profile in cats

Introduction: The objective of this study was to investigate the fermentation kinetics and end products of guar gum in cats. This substrate has never been used before as a songle source of soluble fiber in this species in vivo. Guar gum is, however, considered to be fermentable with a high propionic acid yield based on in vitro data. Materials and Methods: Ten adult cats were fed a commercially available dry cat food, low in protein (27%DM) and without added soluble fiber during a 10-week-period. The cats were divided at random in 2 groups and 4% guar gum or cellulose were supplemented to the diet on DM basis. Both fiber supplements were tested for 5 weeks in a 2x2 Latin square design. Sampling took place during weeks 4 and 5 of every period. Breath samples were collected over a period of 6 hours and the hydrogen concentration was measured immediately. Blood samples were collected for acylcarnitine profile and 3-methylhistidine concentration. Fresh faecal samples were collected for analyses of short-chain fatty acids, ammonia and putrefactive substances. The faecal pH was measured and consistency was scored within 30 minutes after voiding. Results and Discussion: The mean hydrogen concentration of guar gum supplemented cats over all measured time points was numerically higher than for cats supplemented with cellulose. This difference, however, was not statistically significant (P=0.325) and the variation between cats was very high. The faecal pH was significantly lower in the guar gum supplemented cats compared to the cellulose control cats (P=0.003). This result is an indirect proof of a higher production of short-chain fatty acids when guar gum is added to the diet compared to cellulose. For the faecal consistency score a group effect was seen (P=0.008). To date, other analyses were not performed yet. Conclusions: Guar gum is fermented in vivo in cats, as shown from these preliminary data. The numerically higher hydrogen concentration and a significant lower faecal pH in the guar gum supplemented cats compared to the cellulose supplemented cats support this statement

Highly viscous guar gum shifts dietary amino acids from metabolic use to fermentation substrate in domestic cats

The present study evaluated the potential of affecting amino acid metabolism through intestinal fermentation in domestic cats, using dietary guar gum as a model. Apparent protein digestibility, plasma fermentation metabolites, faecal fermentation end products and fermentation kinetics (exhaled breath hydrogen concentrations) were evaluated. Ten cats were randomly assigned to either guar gum- or cellulose-supplemented diets, that were fed in two periods of 5 weeks in a crossover design. No treatment effect was seen on fermentation kinetics. The apparent protein digestibility (P=0.07) tended to be lower in guar gum- supplemented cats. As a consequence of impaired small-intestinal protein digestion and amino acid absorption, fermentation of these molecules in the large intestine was stimulated. Amino acid fermentation has been shown to produce high concentrations of acetic and butyric acids. Therefore, no treatment effect on faecal propionic acid or plasma propionylcarnitine was observed in the present study. The ratio of faecal butyric acid: total SCFA tended to be higher in guar gum- supplemented cats (P=0.05). The majority of large-intestinal butyric acid is absorbed by colonocytes and metabolised to 3-hydroxy-butyrylcoenzyme A, which is then absorbed into the bloodstream. This metabolite was analysed in plasma as 3-hydroxy-butyrylcarnitine, which was higher (P=0.02) in guar gum- supplemented cats. In all probability, the high viscosity of the guar gum supplement was responsible for the impaired protein digestion and amino acid absorption. Further research is warranted to investigate whether partially hydrolysed guar gum is useful to potentiate the desirable in vivo effects of this fibre supplement