Contents

  1. Non starch polysaccharides as nutritive and anti-nutritive factors and their effects on digestion and growth performance.
    1. Introduction:
    2. Digestion of NSPs:
      1. Chemical structure and composition of the feed.
      2. Species and age of animal:
    3. Anti-nutritive effect of NSPs:
      1. Adverse effects of NSPs:
        1. Increased viscosity:
        2. Anti-nutritive effect:
        3. Changes in morphology:
        4. Pathogenic effect:
        5. Tackling the problem:
      2. Other areas of relevance:
  2. Works Cited:

Non starch polysaccharides as nutritive and anti-nutritive factors and their effects on digestion and growth performance.

Introduction:

Non starch polysaccharides (NSPs) along with oligosaccharides are a category of Non starch carbohydrates (NSCs). NSCs in general include a large number of diverse molecules that are able to affect the gut flora of mainly monogastrics where in some cases the effect is beneficial and in others, severe inhibition of the digestive process occurs. These changes include changes in the endocrine, immune and dynamic systems of the gut. The digestibility of different NSCs and therefore different NSPs is highly dependent on the animal species in question, the chemical structure of the NSP molecule, its solubility and also the amount of NSP present.

The interest in carbohydrates and NSPs came about due to two separate disciplines being:

An NSP structure found abundantly in wheat, oat, rye and barley is arabinoxylan. This is constructed of a polymer chain of β,1-4 linked D-xylose sugars with arabinose substitutions along the polysaccharide chain. The arabinose substitutions make arabinoxylan relatively soluble. An insoluble form can also be found when it has no arabinose substitutions. In the case of oat and barley, the main NSPs making up their endosperm cell walls are mixed-link β-glucans, which are made up of glucose chains of variable lengths linked at β,1-4 with intermittent β,1-3 links. The β,1-3 side chains have the same effect as the arabinose subsitutions, in that these make the whole structure soluble, and not allowing the NSP structure to precipitate (Bedford, 1995).

Most studies conducted are on monogastrics since NSPs do not result in digestive problems in digastric animals. The monogastric species studied the most for NSPs and their effects on particular species nutrition, are swine and poultry. This is due to the culture of these two species being very industrialised.

Digestion of NSPs:

Since pigs and poultry have no endogenous enzymes for NSP digestion, digestion relies heavily on chemical digestion by the acid of the stomach of the pig and crop of the chicken, and also microbial degradation. Large intestinal microflora in pigs can digest up to 93% of the NSPs ingested, but in poultry this level of digestion is not reached. The cecum is the site of fermentation in the avian gastro intestinal tract. This is where undigested NSPs and other carbohydrates are transformed into short-chain fatty acids and gases (Józefiak et al, 2004). A study by Carré et al. (1990) reported that digestion of NSPs in adult birds ranged from 21.9% in wheat based diet to 13% in lupin based diet. Therefore NSPs cannot be considered as one entity, due to the multitude of factors that their digestion depends on. The digestion of NSCs and therefore NSPs by microflora in the large intestine of pigs can act result in contributing 50% of dietary energy to the pig. In chicken this value is also much lower where energy obtained by fermentation of this material is that of 24kJ per day which is approximately 2-3% of the dietary energy supply (Choct and Kocher, 2001).

Non starch polysaccharides (NSPs), of 3 different categories (Fig 1.), composed of pentoses and hexoses, are the main materials making up plant cell walls in cereal grains and legume seeds that are used in feedstuffs. These are not hydrolysed by the digestive enzymes secreted by the digestive system, and therefore their more soluble forms tend to produce a viscous mass within the intestinal lumen. This dense viscous mass results in decreased rate of diffusion of substrates and digestive enzymes, and hinders interaction at the surface of absorption. This therefore results in inhibited growth. Insoluble NSPs on the other hand can surround endosperm cells and act as an inhibitory coating which digestive enzymes cannot penetrate (Choct and Kocher, 2001).

Soluble NSPs are more readily digested then insoluble NSPs. In pigs soluble NSPs are nearly completely digested, while insoluble NSPs are only 34 to 60% digested. In poultry soluble NSPs is 12.6% digested in the middle small intestine, and 19.1% digested in the latter part of the small intestine. A study by Carre et al.(1995) though showed that soluble NSPs were 80-90% digested, and non-soluble NSPs were not digested at all. The large difference between the digestion of cellulose and pentosans also suggests that not only solubility but also sugar composition of the NSP is highly determinant for its digestion.

Chemical structure and composition of the feed.

Chemical structure is very important since bacteria and microflora in the intestines can express preference, or even specificity in the utilisation of certain carbohydrate substrates. This arises due to differences in chemical structures. This is observed in pigs in a study conducted by Bach Knudsen K.E. and Hansen I. (1991), where 74 – 88% of β-glucans were digested by the time that they reached the pig ileum, while cellulose, arabinoxylans and uronic acids were totally undigested. When considering digestion through the whole digestive tract, β-glucans were almost completely digested while cellulose from whole wheat flour with pericarp and testa was 34%. When whole wheat flour only was used 60% of the cellulose was digested.

Pentosan is more digestible then cellulose but uronic acids are less digestible. NSPs are generally very similar in digestion regardless of whether they are derived from wheat or oats, but NSPs derived from peas are more digestible than wheat in pigs. NSPs from peas are 85% digestible, while those from wheat are 65% digestible. Component sugars of pea NSPs are almost completely digested by pigs at low levels of inclusions, while they are much less digested in chickens (Choct and Kocher, 2001). The cell wall structure is also affects greatly the digestibility of its NSP components. Some factors of cell wall structure are:

Species and age of animal:

One could observe a large difference between swine and poultry digestion of NSPs. Pigs digest NSPs better due to more intense fermentation of NSPs in the large intestine by bacteria and also longer digesta transit time, due to a longer digestive tract (Choct and Kocher, 2001). Mathers (1991) states that when NSP digestion differences between swine and humans were studied, it resulted that NSP in swine was completely digested when it passed through the upper intestine while relatively little NSP was digested in the human examples. He also states that by reducing transit time of the digesta, there was a minimal effect on the faecal output of the major pentose sugars but an increased output of cellulose was observed. This is because cellulose is usually the NSP fraction with lowest digestibility and therefore a shorter time exposed to microbial fermentation results

Age also plays a role in the digestion of NSPs; adults manage to digest more NSPs then juveniles. Pentosan digestibility in a two week old broiler is approximately 4%, while in an adult it is approximately 19%. This suggests a development of NSP digesting microflora as birds become older. This also reflected in an inverse relationship of gut viscosity with age in birds fed barley where gut viscosity decreased as birds got older and microflora produce more glycanases (Choct and Kocher, 2001; Mathers, 1991).

Anti-nutritive effect of NSPs:

Adverse effects of NSPs:

Increased viscosity:

High level of NSPs, especially the soluble fraction, leads to a decrease in nutrient digestion and therefore a decrease in the absorption of nutrients. This mostly occurs in poultry and also to a certain extent in pigs. Soluble NSPs lead to an increase of viscosity of the digesta which leads to changes in physiology and ecosystem of the gut. This occurs since NSPs having long polysaccharide chains get entangled when in a dissolved state causing an increase in gut content viscosity (Choct and Kocher, 2001). In a study investigating the effect of NSPs in triticale based combined broiler diet Stef et al. (2011) it was stated that wheat, rye and triticale all contain a significant proportion of arabinoxylans. These arabinoxylans are soluble NSPs which in turn results in increased digesta viscosity. In another study goslings fed a diet rich in highly insoluble NSPs had significantly better feed intake, weight gain, and feed conversion ratio then goslings fed a highly soluble NSP rich diet (Lin et al, 2010).

Increased chime viscosity will result in reduced gastric emptying leading to a feeling of satiety and therefore reduced feed intake by the animals (Lin et al, 2010). Slow moving digesta in a low oxygen environment could provide a very stable habitat for excessive fermentation to take place. Choct et al. (1996) demonstrated a large increase in fermentation in small intestine of broilers by adding soluble NSPs in their diet. A high amount of volatile fatty acids produced by the digestion of NSPs may not necessarily result in increased nutritional content of the feed. This is because the drastic changes in the gut ecosystem result in impoverished nutrition, and therefore lower performance. This was alleviated when glycanases were used in order to digest NSPs (Choct and Kocher, 2001).

Anti-nutritive effect:

NSPs also have the property of binding nutrients and form complexes with digestive enzymes and some regulatory proteins during the process of digestion in the gut, resulting in inhibition of these digestive processes. Soluble NSPs significantly increase endogenous losses of amino acids in chicken digestion. NSPs were also found to enhance excess bile acid secretion in rats, resulting in a significant loss in bile acids. This occurs due to the binding of bile salts, lipids and cholesterol which in turn could result in the increased synthesis of bile acids from cholesterol, in an attempt to restore normal levels in hepatic circulation. Due to the sequestrative nature of NSPs, changes in the absorptive and digestive dynamics of the gut occurs due to sequestration of bile acids and lipids, which can result in increased elimination of acidic faeces and neutral sterols. This binding results in poor absorption of lipids and cholesterol in the intestine, leading to poor efficiency (Choct and Kocher, 2001). A study by Fang et al. (2007) states that NSPs can also inhibit the absorption of carbohydrates such as starch and free sugars by a process called encapsulation and it can also inhibit protein absorption, since proteins are covalently bound to cell wall carbohydrates. The action of hydrolysing endogenous enzymes, relieves this encapsulating effect. This study by Fang and his colleagues (2007) also shows that enzyme supplementation resulted in clearly improved growth and feed conversion ratio in swine.

Changes in morphology:

In an experiment by Lin et al. (2010) a pectin rich diet was found to have a very significant effect on the morphology of the digestive tract of one day old white roman female goslings. Goslings fed the pectin diet had heavier and larger proventriculus, gizzard, liver and pancreas then those being fed the maize, barley hull, rice bran and wheat bran diets. This though resulted in lower specific activities for amylase, lipase, trypsin and chymotrypsin enzymes in goslings receiving the pectin diet. Due to the combined effects of decreased activity of pancreatic enzymes, digestive upset and inhibition and bad palatability of the feed (due to the stickiness of the feed in the beak of the animal) goslings being fed the pectin diet demonstrated stunted growth (Lin et al, 2010).

Pathogenic effect:

An in gut microflora due to increased NSP usage can also result in microbial diseases such as, swine dysentery in weaner pigs, and high necrotic enteritis in poultry. These pathogenic effects can be alleviated by the introduction of hydrolysing enzymes, which can act on the NSPs. After hydrolysing enzyme supplementation in poultry, there was an observable decrease in Clostridium perfringens population numbers which in turn resulted in a decrease in necrotic enteritis cases (Choct and Kocher, 2001).

Tackling the problem:

The inclusion of xylanase enzyme, as supplementation to the triticale based broiler diet, resulted in a reduction of duodenum and jejunum viscosity by 15%, and also as an increase by 10% in body weight, resulting in a better feed conversion ratio. Therefore, the incorporation of 40 to 60% triticale as a feed substrate, is only possible if enzymes such as xylanases are used (Stef, et al., 2011). NSP degrading enzymes such as xylanases, are thought to work in two steps called the ileal and the cecal phase, where in the ileal phase, enzymes remove fermentable substrates and in the cecal phase degradation products of sugars are fermented by bacteria in the cecum, producing volatile fatty acids (Luo, et al., 2009). In another study involving pigs fed corn-based diets supplemented with 10% Chinese double-low rapeseed meal (DLRM), multiple enzyme treatment was more effective than using xylanase only treatment in the digestion of NSPs, but the experiment also showed that both nutrient supplementation indicated an effective improvement in hydrolysis of NSPs in the digestive tracts of growing pigs, resulting in better digestibility and performance. This occurs since, DLRM has different types of NSP structures (arabinose (33%), xylose (13%), mannose (3%), rhamnose (2%), fucose (2%), uronic acids (30%), galactose (13%) and glucose (5%)) and therefore one specific enzyme was not sufficient (Fang et al, 2007).

Apart from enzyme supplementation, extrusion cooking or baking resulted in a slight increase in digestibility for pigs, with the xylose-containing NSPs being least digested, and the β-glucans being totally digested for both raw and extrusion cooked diets (Mathers, 1991).

The production of transgenic animals that can produce NSP degrading enzymes, are being considered as an option. This is sought to be done by the incorporation of various enzyme encoding genes derived from bacterial and fungal sources, into the mammalian or avian genome. This may result into the development of non-ruminant livestock, that can secrete NSP-degrading enzymes. Genes isolated so far are those coding for enzymes for the degradation of cellulose xylans, pectin and β-glucans. The main problem with this approach is that NSPs are a very large group of polysaccharides, and different specific enzymes are used to act on this great variety of structures. This results in the need of incorporating a lot of enzyme encoding genes in the livestock genome, which is a very difficult and arduous process (Mathers, 1991).

Other areas of relevance:

Research is also being conducted in aquaculture, so as to improve feed conversion ratio, especially in the culture of carnivorous species. The interest in the digestion of NSPs and other feed substrates, in aquaculture, is not solely due to its antinutritional effect and the digestive problems these may cause but also because these can act as protein and energy sources that may aid in the reduction of fish meal in carnivorous fish diets.

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Works Cited:

Bach Knudsen, K., Hansen, I. (1991). Gastrointestinal implications in pigs of wheat and oat fractions. Digestibility and bulking properties of polysaccharides and other major consituents. The British Journal of Nutrition, 65(2), 217-232.

Bedford, M. (1995). Mechanism of action and potential environmental benefits from the use of feed enzymes. Animal Feed Science and Technology, 53, 145-155.

Carré, B., Derouet, L., Leclercq, B. (1990). The digestibility of cell-wall polysaccharides from wheat (bran or whole grain), soybean meal, and white lupin meal in cockerels, muscovy ducks, and rats. Poultry Science., 69(4), 623-633.

Carré, B., Gomez, J., Chagneau, A. (1995). Contribution of oligosaccharide and polysaccharide digestion, and excreta losses of lactic acid and short chain fatty acids, to dietary metabolisable energy values in broiler chickens and adult cockerels. British Poultry Science, 36(4), 611-629.

Choct, M., Kocher, A. (2000). Non-starch carbohydrates: Digestion and its secondary effects in monogastrics. Proceedings of the Nutrition Society of Australia., 24, 31-38.

Fang, Z., Peng, J., Liu, Z., Liu, Y. (2007). Responses of non-starch polysaccharide-degrading enzymes on digestibility and performance of growing pigs fed a diet based on corn, soya bean meal and Chinese double-low rapesead meal. Journal of Animal Physiology and Animal Nutrition, 91, 361-368.

Józefiak, D., Rutkowski, A., Martin, S. (2004). Carbohydrate fermentation in the avian ceca: a review. Animal Feed Science and Technology, 113, 1-15.

Lin, P., Shih, B., Hsu, J. (2010). Effects of different sources of dietary non-starch polysaccharides on the growth performance, development of digestive tract and activities of pancreatic enzymes in goslings. British Poultry Science, 51(2), 270-277.

Luo, D., Yang, F., Yang, X., Yao, J., Shi, B., Zhou, Z. (2009). Effects of Xylanase on Performance, Blood Parameters, Intestinal Morphology, Microflora and Digestive Enzyme Activities of Broilers Fed Wheat-based Diets. The Asian-Australian Journal of Animal Science., 22(9), 1288-1295.

Mathers, J. (1991). Digestion of Non-Starch Polysaccharides by Non-Ruminant Omnivores. Proceedings of the Nutritional Society, 50(2), 161-172.

Stef, L., Drinceanu, D., Julean, C., Căpriţă, R., Stef, D., Pandur, C., Fota, D. (2011). Assessment and Control of the Antinutritional Effect Exerted by Non-Starch Polysaccharides from Triticale-Based Combined Forage, in Broilers. Scientific Papers:Animal Science and Biotechnologies, 44(1), 125 - 130.

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Non-starch_Polysaccharides (last edited 2012-12-05 20:13:35 by 2241E)