Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats. I. Studies with protein-free diets

Regulation of dietary fiber on intestinal microorganisms and its effects on animal health

The animal gut harbors diverse microbes that play an essential role in the well-being of their host. Specific diets, such as those rich in dietary fiber, are vital in disease prevention and treatment because they affect intestinal flora and have a positive impact on the metabolism, immunity, and intestinal function of the host. Dietary fiber can provide energy to colonic epithelial cells, regulate the structure and metabolism of intestinal flora, promote the production of intestinal mucosa, stimulate intestinal motility, improve glycemic and lipid responses, and regulate the digestion and absorption of nutrients, which is mainly attributed to short-chain fatty acids (SCFA), which is the metabolite of dietary fiber. By binding with G protein-coupled receptors (including GPR41, GPR43 and GPR109A) and inhibiting the activity of histone deacetylases, SCFA regulate appetite and glucolipid metabolism, promote the function of the intestinal barrier, alleviate oxidative stress, suppress inflammation, and maintain immune system homeostasis. This paper reviews the physicochemical properties of dietary fiber, the interaction between dietary fiber and intestinal microorganisms, the role of dietary fiber in maintaining intestinal health, and the function of SCFA, the metabolite of dietary fiber, in inhibiting inflammation. Furthermore, we consider the effects of dietary fiber on the intestinal health of pigs, the reproduction and lactation performance of sows, and the growth performance and meat quality of pigs.

The role of dietary fibre in pig production, with a particular emphasis on reproduction

Fibres from a variety of sources are a common constituent of pig feeds. They provide a means to utilise locally-produced plant materials which are often a by-product of the food or drink industry. The value of a high fibre diet in terms of producing satiety has long been recognised. However the addition of fibre can reduce feed intake, which is clearly detrimental during stages of the production cycle when nutrient needs are high, for example in growing piglets and during lactation. More recently, fibre has been found to promote novel benefits to pig production systems, particularly given the reduction in antimicrobial use world-wide, concern for the welfare of animals fed a restricted diet and the need to ensure that such systems are more environmentally friendly. For example, inclusion of dietary fibre can alter the gut microbiota in ways that could reduce the need for antibiotics, while controlled addition of certain fibre types may reduce nitrogen losses into the environment and so reduce the environmental cost of pig production. Of particular potential value is the opportunity to use crude fibre concentrates as ‘functional’ feed additives to improve young pig growth and welfare. Perhaps the greatest opportunity for the use of high fibre diets is to improve the reproductive efficiency of pigs. Increased dietary fibre before mating improves oocyte maturation, prenatal survival and litter size; providing a consumer-acceptable means of increasing the amount of saleable meat produced per sow. The mechanisms responsible for these beneficial effects remain to be elucidated. However, changes in plasma and follicular fluid concentrations of key hormones and metabolites, as well as effects of the hypothalamic satiety centre on gonadotrophin secretion and epigenetic effects are strong candidates.

Differential response of protein metabolism in splanchnic organs and muscle to pectin feeding

The aim of the present study was to determine whether the addition of soluble fibre in the diet affected protein metabolism in the intestinal tissues, some visceral organs and in skeletal muscle. A diet supplemented with pectin (80 g/kg) was fed to young growing rats and the effect on organ mass and protein metabolism in liver, spleen, small and large intestines and gastrocnemius muscle was monitored and compared with the control group. Protein synthesis rates were determined by measuring [13C]valine incorporation in tissue protein. In the pectin-fed rats compared with the controls, DM intake and body weight gain were reduced (9 and 20 %, respectively) as well as gastrocnemius muscle, liver and spleen weights (6, 14 and 11 %, respectively), but the intestinal tissues were increased (64 %). In the intestinal tissues all protein metabolism parameters (protein and RNA content, protein synthesis rate and translational efficiency) were increased in the pectin group. In liver the translational efficiency was also increased, whereas its protein and RNA contents were reduced in the pectin group. In gastrocnemius muscle, protein content, fractional and absolute protein synthesis rates and translational efficiency were lower in the pectin group. The stimulation of protein turnover in intestines and liver by soluble fibre such as pectins could be one of the factors that explain the decrease in muscle turnover and whole-body growth rate.

Dietary pectin stimulates protein metabolism in the digestive tract

OBJECTIVE

The aim of this study was to determine if protein metabolism was altered in small and large intestines by feeding pectin, a soluble fiber known to stimulate cecal production of short-chain fatty acids (SCFAs) and to have a trophic effect in these tissues.

METHODS

Twenty-four weanling male Sprague-Dawley rats were fed ad libitum for 14 d with a balanced control diet or an isoproteic, isocaloric pectin (citrus) diet (80 g/kg). SCFA production, intestinal histomorphometry, and protein synthesis were determined in the proximal and distal parts of the small intestine, the cecum, and the colon. Protein synthesis rates were determined by measuring the (13)C valine incorporation rate in tissue proteins.

RESULTS

Pectin feeding slightly decreased food intake and growth rate. It increased the acetate, propionate, and butyrate pools in the cecum. Pectin feeding resulted in heavier intestinal tissues corresponding to higher villus height in the small intestine and crypt depth in the small and large intestines compared with feeding of the control diet. Compared with the control group, the rats fed the pectin diet had significantly higher protein synthesis rates in all the parts of their intestines.

CONCLUSION

Supplementation of pectin, as a soluble fiber, in the diets, stimulated SCFA production, had a trophic effect on the different parts of the intestines, and greatly stimulated protein synthesis in those tissues.

Biological properties of fructooligosaccharides with different contents of kestose and nystose in rats

In a four-week experiment on rats' diets containing 5% of sucrose or fructooligosaccharides (FOS) diversified in terms of kestose and nystose contents: 6:1 (FOS-K), 3:1 (FOS-KN), and 0.5:1 (FOS-N) were applied. All FOS preparations, primarily FOS-N, considerably increased the mass of caecum, lowered pH of caecal digesta, and increased concentrations of protein. The glycolytic activity of the caecal digesta was generally alike in all groups, except for the control group where the activity of beta-glucosidase was negligibly lower and that of alpha-galactosidase higher. The administration of FOS preparation with a diet increased the concentration and the pool of total VFA in the caecal digesta, especially in the case of butyric and propionic acids and decreased the concentration of iso-butyric and valeric acids. When compared with the kestose-rich preparation, the nystose-rich preparation increased the production of total VFA in the caecum, primarily of n-butyrate and propionate. Different length of kestose and nystose chains had no effect on the activity of bacterial enzymes in the caecum nor the biochemical indices of serum, concentration of cholesterol, glucose, urea, Ca, P and Mg.

Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats. II. Studies with diets differing in protein quality

In 2 two-factorial experiments, each conducted on 80 growing male rats, the effects of substituting 10% raw potato starch (PS), pectins (PEC), or cellulose (CEL) for wheat starch (WS) and the addition of tannic acid to WS (WSTA) were studied using diets differing in protein quality. Casein unsupplemented or supplemented with DL-methionine and gluten unsupplemented or supplemented with lysine, methionine and tryptophan were used as protein sources in Experiment 1 and 2, respectively. Parameters indicative of caecal fermentation intensity (pH, acetic, propionic and butyric acid contents, digesta and tissue weight) and of protein metabolism (urea blood concentration, faecal and urinary nitrogen excretion) were determined. Ten-day balance experiments were preceded by a 10-day adaption period to respective carbohydrates given in a diet containing balanced protein. In both experiments the type of carbohydrates affected the caecal concentration of individual and total SCFA and other parameters of fermentation intensity. Pectins and potato starch were fermented more intensively than cellulose. Faecal N excretion was increased by all carbohydrates substituted for cereal starch, and by tannic acid. Urinary excretion was greater on CEL than on PEC and WSTA containing casein and on other diets containing gluten. In both experiments urinary N excretion was the lowest on PEC diets. Protein quality had the greatest effect on apparent biological value and net protein utilization but all indices of protein utilization were also affected by carbohydrates. It is concluded that not only the amount of N excreted in faeces but also in urine is affected by the type and fermentability of carbohydrates.