Non-starch polysaccharides

Non-starch polysaccharides (NSP) belong to the group of dietary carbohydrates. They are non-starch macromolecular polymers of monosaccharides linked by glycosidic bonds with a degree of polymerization of ten and more (CUMMINGS u. STEPHEN 2007; ENGLYST et al. 2007). In mammals and birds NSP cannot be degraded by endogenous enzymes of the animal and are considered as prebiotics. The fermentation of NSP occurs mainly in cecum and colon by intestinal bacteria (CUMMINGS u. MACFARLANE 1997; BAKKER et al.

1998; WATZL et al. 2005; ROBERFROID 2006; WESTENDARP 2006). According to their physical properties, they can be divided into water-soluble and water-insoluble fractions, which is of relevance for their nutritional value (SPILLER 1994).

Soluble NSP include pectins, pentosans, fructans, beta-glucans and carboxymethylcellulose.

Inulin is a naturally occurring polysaccharide, which is often used as a source of soluble NSP in animal nutrition. Soluble NSP are known to possess anti-nutritional properties by encapsulating nutrients and preventing access of digesting enzymes, or by changing the microbial composition and activity in the intestine (BEDFORD u. CLASSEN 1992; CHOCT et al. 1996; PLUSKE et al. 1998; JENKINS et al. 1999; MCDONALD et al. 1999; JAMROZ et al. 2002). Furthermore, they increase viscosity of the digesta and slow down the passage rate of nutrients (CHOCT u. ANNISON 1992; DUSEL et al. 1997; LIN et al. 2010).

Cellulose and arabinoxylans belong to the insoluble NSP. Feed components such as rice shells and straw powder are especially rich in insoluble NSP. They increase the intestinal passage of nutrients and the volume of digesta. Insoluble NSP are considered to reduce microbial activity and pathogenicity of bacterial populations in the intestine due to their laxative effect (LEESON et al. 1991; SMITS u. ANNISON 1996; DURMIC et al. 1998; VAN KRIMPEN et al. 2009).

2.6.1. Local and systemic effect of NSP on the immune system

Extensive studies in mammals have demonstrated that NSP may modulate systemic and especially local gut-associated immune functions (ROLLER et al. 2004a; ROLLER et al.

2007; BODERA 2008; MEYER 2008; KELLY 2009). Most of these studies have focused on the role of soluble NSP (inulin) on the immune system.

NSP showed various immunomodulatory effects in the T- and B lymphocyte compartment in mammalian species (MANHART et al. 2003; WATZL et al. 2005; KRAG et al. 2006).

Addition of dietary inulin and oligofructose to the diet of rats has led to an increase in T lymphocytes and major histocompatibility complex II molecules in splenic, thymus and mesenteric lymph node (MLN) cells (TRUSHINA et al. 2005). Oral administration of NSP induced proliferation of IgA-producing B lymphocytes in the intestinal mucosa of rats (KUDOH et al. 1998). Pectin in the diet of rats significantly increased the CD4+/CD8+ ratio in MLN lymphocytes (LIM et al. 1997).

Also, local and systemic cytokine production levels, as well as concentration of secretory IgA in ileum and cecum may be influenced by NSP (SEIFERT u. WATZL 2007). Inulin enriched with oligofructose enhanced the production of IL-10 in Peyer's patches as well as the concentration of secretory IgA in the cecum of rats (ROLLER et al. 2004b). Addition of fructooligosaccharides to the diet of mice induced increased production of IFN-γ, IL-10, IL-5 and IL-6 by CD4+ cells in Peyer's patches (HOSONO et al. 2003). Inulin-fed rats showed a higher ex vivo secretion of IL-2, IL-10 and IFN-γ in spleen and mesenteric lymph node cell cultures, as well as a higher proportion of dendritic cells in the Peyer’s patches (RYZ et al.

2008).

Not much information is available how NSP may modulate the immune system of birds.

Recently, it has been shown, that fructo-oligosaccharide reduced the proportion of B cells but did not affect the percentage of T cells in cecal tonsils, and enhanced IgG antibody titers in plasma of broiler chicken (JANARDHANA et al. 2009).

The investigations in mammalian models demonstrated that NSP primarily modulate immune parameters on the GALT level, but it may also come to a systemic activation of leukocytes in the spleen. The production of short-chain fatty acids (SCFA) which bind to SCFA-receptors on leucocytes, or direct influence of lactic acid-producing microorganisms on immune cells are considered to be responsible for the immuno-modulating effects (WATZL et al. 2005).

2.6.2. Effect of NSP on nematode infections

Until now most of the studies investigating the effects of NSP on nematode infections were performed in mammalian models. It was shown that dietary fibre has an influence on parasite establishment and survival in the host (PEARCE 1999; THOMSEN et al. 2006). This influence was shown to be associated with water-soluble and water-insoluble properties of NSP. Inclusion of soluble NSP such as inulin in the diet of pigs infected with Trichuris suis or Oesophagostomum dentatum led to a significant reduction in worm establishment, egg excretion and female worm fecundity (PETKEVICIUS et al. 2003; THOMSEN et al. 2005;

KRAG et al. 2006; PETKEVICIUS et al. 2007). In contrast, diets enriched with insoluble NSP provide favourable conditions for the establishment and survival of Oesophagostomum dentatum in the large intestine of pigs (PETKEVICIUS et al. 1997; PETKEVICIUS et al.

1999; PETKEVICIUS et al. 2001). Opposing results to those collected throughout experiments in pigs were demonstrated in a study in mice infected with Heligmosomoides polygyrus. The parasite establishment was elevated, when the animals were fed a pectin-enriched diet, whereas cellulose did not affect establishment, reproduction and survival of the parasite (SUN et al. 2002).

A study with A. galli-infected chicken demonstrated a reduction in the number of worms and fecal egg shedding rate, when the birds were fed a soluble NSP enriched diet, which

additionally was supplemented with NSP-hydrolyzing enzyme (DÄNICKE et al. 2009). The actual influence of soluble and insoluble NSP in nematode infections in birds has not been yet investigated.

The exact mechanism of the influence of dietary fibre on the course of nematode infections is still unknown. It is suggested that microbial degradation of NSP induce changes in bacterial populations of intestinal microflora and their metabolic products, such as concentrations of short-chain fatty acids and lactic acids, which may have an impact on helminth survival (PETKEVICIUS et al. 2004).