A review of interactions between dietary fibre and the intestinal mucosa, and their consequences on digestive health in young non-ruminant animals

Viscosity is a physicochemical property associated with dietary fibers, particularly soluble dietary fibers. Viscous dietary fibers thicken when mixed with fluids and include polysaccharides such as gums, pectins, psyllium, and β-glucans. Although insoluble fiber particles may affect viscosity measurement, viscosity is not an issue regards insoluble dietary fibers. Viscous fibers have been credited for beneficial physiological responses in human, animal, and animal-alternative in vitro models. The following article provides a review of viscosity as related to dietary fiber including definitions and instrumentation, factors affecting viscosity of solutions, and effects of viscous polysaccharides on glycemic response, blood lipid attenuation, intestinal enzymatic activity, digestibility, and laxation.

Viscosity as Related to Dietary Fiber: A Review

Diets fed to nonruminant animals are composed mainly of feed ingredients of plant origin. A variety of antinutritional factors such as phytin, nonstarch polysaccharides, and protease inhibitors may be present in these feed ingredients, which could limit nutrients that may be utilized by animals fed such diets. The primary nutrient utilization-limiting effect of phytin arises from the binding of 6 phosphate groups, thus making the P unavailable to the animal. The negative charges allow for formation of insoluble phytin-metal complexes with many divalent cations. Furthermore, phytin and protein can form binary complexes through electrostatic links of its charged phosphate groups with either the free amino group on AA on proteins or via formation of ternary complexes of phytin, Ca(2+), and protein. The form and extent of de novo formation of binary and ternary complexes of phytin and protein are likely to be important variables that influence the effectiveness of nutrient hydrolysis in plant-based diets. Nonstarch polysacharides reduce effective energy and nutrient utilization by nonruminant animals because of a lack of the enzymes needed for breaking down the complex cell wall structure that encapsulate other nutrients. Enzymes are used in nonruminant animal production to promote growth and efficiency of nutrient utilization and reduce nutrient excretion. The enzymes used include those that target phytin and nonstarch polysaccharides. Phytase improves growth and enhances P utilization, but positive effects on other nutrients are not always observed. Nonstarch polysaccharide-hydrolyzing enzymes are less consistent in their effects on growth and nutrient utilization, although they show promise and it is imperative to closely match both types and amounts of nonstarch polysaccharides with appropriate enzyme for beneficial effects. When used together with phytase, nonstarch polysaccharide-hydrolyzing enzymes may increase the accessibility of phytase to phytin encapsulated in cell walls. The future of enzymes in nonruminant animal production is promising and will likely include an understanding of the role of enzyme supplementation in promoting health as well as how enzymes may modulate gene functions. This review is an attempt to summarize current thinking in this area, provide some clarity in nomenclature and mechanisms, and suggest opportunities for expanded exploitation of this unique biotechnology.

BOARD-INVITED REVIEW: opportunities and challenges in using exogenous enzymes to improve nonruminant animal production.

Early weaning of piglets is often accompanied by a severe growth check and diarrhoea. It is well established that this process is multi-factorial and that post-weaning anorexia and under-nutrition are major aetiological factors. Gastrointestinal disturbances include alterations in small intestine architecture and enzyme activities. Recent data indicate transiently-increased mucosal permeability, disturbed absorptive-secretory electrolyte balance and altered local inflammatory cytokine patterns after weaning. These responses appear to operate according to two distinct temporal patterns, an acute response followed by a long-lasting adaptation response. Pigs coexist with a diverse and dense commensal microbiota in their gastrointestinal tract. Most of these microbes are beneficial, providing necessary nutrients or protection against harmful pathogens for the host. The microbial colonisation of the porcine intestine begins at birth and follows a rapid succession during the neonatal and weaning period. Following the withdrawal of sow's milk the young piglets are highly susceptible to enteric diseases partly as a result of the altered balance between developing beneficial microbiota and the establishment of intestinal bacterial pathogens. The intestinal immune system of the newborn piglet is poorly developed at birth and undergoes a rapid period of expansion and specialisation that is not achieved before early (commercial) weaning. Here, new insights on the interactions between feed components, the commensal microbiota and the physiology and immunology of the host gastrointestinal tract are highlighted, and some novel dietary strategies are outlined that are focused on improving gut health. Prebiotics and probiotics are clear nutritional options, while convincing evidence is still lacking for other bioactive substances of vegetable origin.

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Nutritional management of gut health in pigs around weaning.

Non-starch polysaccharides and their role in fish nutrition – A review

Sources of viscous soluble fibre, such as barley and oats, have often been included in the weaning diet of the pig to accelerate development of the large intestine. Inclusion of a non-fermentable, viscous compound, sodium carboxymethylcellulose (CMC), in a low-fibre weaning diet was tested to assess the influence of digesta viscosity on the gut in the absence of increased fermentation. Two CMC sources, of low and high viscosity, were added to cooked rice-based diet at 40 g/kg total diet. A third control rice diet did not contain any CMC. Diets were fed for 13 d following weaning at 3 weeks of age. Addition of CMC to the diet significantly increased the intestinal viscosity of digesta within the small (P<0.001) and large (P<0.05) intestine. No simple association was found between increases in intestinal viscosity and effects on intestinal morphology and whole-body growth. The average empty-body-weight gain and the small intestinal villus height increased with low-viscosity CMC, but decreased with the high-viscosity CMC group. The full large intestinal weight increased in all pigs fed CMC. Dietary CMC (both low- and high-viscosity) increased the percentage moisture of digesta and faeces, and was associated with increased faecal shedding of enterotoxigenic haemolytic Escherichia coli. Feed ingredients in weaning diets that excessively increase the viscosity of the intestinal digesta may be detrimental to pig health and production.

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Increasing viscosity of the intestinal contents alters small intestinal structure and intestinal growth, and stimulates proliferation of enterotoxigenic Escherichia coli in newly-weaned pigs

Adverse effects of soluble non-starch polysaccharide (guar gum) on piglet growth and experimental colibacillosis immediately after weaning

Carbohydrates comprise between 60% and 80% of the digestible dry matter (DM) in the majority of feedstuff for weaner pigs. The carbohydrate ingested by piglets can be divided into one fraction (starch) that is targeted by the endogenous enzymes of the gastrointestinal tract (a-amylase), and another component (‘dietary fibre’, DF) that is digested predominantly in the terminal ileum and large intestine. The major constituent of DF in diets for young pigs influencing production, gut function and possibly enteric disease susceptibility is derived from non-starch polysaccharides (NSPs). Traditionally the ‘indigestible’ carbohydrate content of foodstuffs has been expressed as ‘crude fibre’, a term that provides no information regarding possible physico-chemical effects of NSP in vivo in the animal or its likely digestibility; simply because it is the residue remaining from extractions of the major plant cell wall components.

Non-starch polysaccharides are a large variety of polysaccharide molecules, often in association with phcnolic lignified polymers, protein and starch, that have glucosidic bonds other than the α-(1→4), (1→6) bonds of starch. The building blocks of plant cell wall polysaccharides are the pentoses (arabinose and xylose), hexoses (glucose, galactose and mannose), 6-deoxyhexoses (rhamnose and fucose) and uronic acids (glucuronic and galacturonic acids). These monomers are chemically linked to each other to build various NSPs in the plant cell walls of both cereals and legumes. The major NSPs of plant cell wails, therefore, comprise cellulose (linear β-glucan chains), non-cellulosic polysaccharides (arabinoxylans, mixed-linked β-glucans, mannans, galactans, xyloglucan) and pectic polysaccharides (polygalacturonic acids, which may be substituted with arabinan, galactan and arabinogalactan) (Theander et al, 1989; Lewis, 1993; Bach Knudsen, 1997; Choct, 1997). The NSPs, in turn, can be divided into the ‘soluble’ fraction and the ‘insoluble’ fraction. The term ‘soluble’ refers to solubility in water or weak alkali solutions. It is generally accepted that the large majority of NSPs exhibiting anti-nutritive properties in monogastric animals, or at least the broiler chicken, are water-soluble and give rise to viscous aqueous solutions even when present at relatively low levels (Annison, 1993). 

The major polysaccharides present in grains and legumes are presented (as average values) in Table 5.1. However, and from a physiological perspective, it is important to consider also the variation that exists within a particular cereal, because this may deter mine some of the physicochemical properties of the grain in vivo that, in turn, are likely to have an effect on digestibility and performance. Further discussion of the implications of this variation will be discussed later in this chapter.

Non-starch polysaccharides in the diets of young weaned piglets.

Blood samples were collected from 40 emus (Dromaius novaehollandiae) of 4 different age groups ranging from 1 week to 14 months. Plasma values of glucose, cholesterol, uric acid, total protein, albumin, creatine kinase, aspartate amino transferase, alkaline phosphatase, calcium, phosphorus and magnesium were measured. Fourteen-month-old birds had lower plasma glucose values and enzyme activities and higher plasma protein values than younger birds. One-week-old birds had higher cholesterol and uric acid values than other age groups. Plasma calcium, phosphorus and magnesium values did not differ across the age profiles sampled.

Age‐related changes in plasma biochemical values of farmed emus (Dromaius novaehollandiae)

The performance and health of weaner pigs (n=40) was compared between pigs fed either a rice-based weaner pig diet or the same diet with pearl barley included at 50% weight of the air-dry diet. Within each dietary treatment, two-thirds of the pigs were infected with enterotoxigenic Escherichia coli O8:K88:K87 at 48, 72 and 96 h post-weaning; the remaining third were healthy controls. Compared with htose fed the barley diet, pigs fed the rice-only diet grew faster, had less intestinal proliferation of E. coli, and exhibited less severe diarrhoea. It appears that the soluble non-starch polysaccharides (sNSP) in barley are detrimental to the performance of both healthy weaner pigs and those with postweaning colibacillosis (PWC)

D.E. McDonald

Papers

Increasing viscosity of the intestinal contents alters small intestinal structure and intestinal growth, and stimulates proliferation of enterotoxigenic Escherichia coli in newly-weaned pigs

Adverse effects of soluble non-starch polysaccharide (guar gum) on piglet growth and experimental colibacillosis immediately after weaning

Non-starch polysaccharides in the diets of young weaned piglets.

Age‐related changes in plasma biochemical values of farmed emus (Dromaius novaehollandiae)

Soluble non-starch polysaccharides from pearl barley exacerbate experimental postweaning colibacillosis