Feed contributes about 70% of total expenses required for the modern poultry enterprises in general. As the days go by, the issue is becoming a cause of concern and it becomes almost mandatory to rethink on the feeding strategies to make the enterprises profitable & sustainable as well. Since the major reason for the concern is the rise in prices of various feedstuffs thus as a consequence practice to utilize comparatively cheaper and unconventional feed ingredients becomes time demanded. The utilization of the naturally undigested parts in the diet is also another smart option in these strategies. Non-Starch Polysaccharides (NSPs) are of that kind and can be the top most priority. Proper understanding of NSPs and about their anti-nutritional effects allows efficient use of this in substantially reduction of feed cost and make the business overall more profitable.
NSPs in poultry feedstuffs:
NSPs are polymers of carbohydrates differ in composition and structure from starch. It has chemical cross linking among them, therefore are not well digested by poultry birds. It differs greatly in different feedstuffs. (Figure 1). NSPs content in feedstuffs make exclusively the part of the cell wall. Cellulose is here a linear chain of glucose sugar and considered as an inert non-fermentable fiber in the diet. Whereas hemicellulose consists of different types of sugars and flexible compared to cellulose. In general, cell wall in feedstuffs can be imagined as a woven net, cellulose is the “cables” here, whereas hemicelluloses are the ‘net’ woven in and around the ‘cables. The woven complexes encapsulate the starch and other necessary nutrients in traps. The monosaccharides, the units of polymer, mainly present in cereal cell wall are: (1) hexoses; D-glucose, D-galactose, D-mannose; (2) pentoses; L-arabinose, D-xylose, and (3) acidic sugars; D-galacturonic acid, D-glucuronic acid and its 4-O-methyl ether.
In the complex, NSPs have been classified into following 3 groups- (i) Cellulose, a polysaccharide consisting of a linear chain of β 1, 4 linked D-glucose units, comprises a sole component of the cell wall. (ii) Non-Cellulosic Polymers, commonly called hemicelluloses includes Arabinoxylans (AX), mixed linked beta glucans, mannans, galactans & Xyloglucan. (ii) Pectic polymers, the Polygalacturonic acid substituted with Arabinan, Galactan & Arabinogalactan. This is mainly found in stems and leaves of cereals.
On the other hand, depending on the fractions soluble in water, NSPs can be classified into water soluble and water insoluble and this brings special importance in context to poultry nutrition.
(i) Soluble NSPs: Rye, wheat, barley, Oat, triticale is considered as viscous feedstuffs because of its high content of soluble fractions. Use of this increases the viscosity of intestinal viscosity and thereby interferes with the digestive processes and causes negative effects on nutrient utilization. Increased viscosity of digesta slower the passage through GIT reduces feed intake & digestibility. It may alter gut physiology by enlargement of the GIT and hamper the formation of enzyme substrate complex due to decrease the surface area in compared to the volume. Soluble NSPs can also be used in lean meat broiler production as it helps in reduction of blood & body cholesterol by exerting bile without act upon the digesta. Thus, to compensate it more bile salts produced by metabolizing the cholesterol and liver increases its LDL receptors thus further absorbing cholesterol from blood lowering the body cholesterol level. (ii) Insoluble NSPs: Corn, sorghum, rice is the no viscous because of its high content of insoluble NSPs. They affect gut functions and modulate nutrient digestion by favoring gizzard function to regulate digesta passage rate and nutrient digestion in the intestine. As these are not degraded by endogenous enzymes and reach the colon carrying a significant amount of encapsulated nutrients. Thus, it is considered as a potential anti-nutritional factor in poultry diet.
Therefore, without treating feed with exogenous enzymes NSPs can bring some benefits in production of lean meat broiler (soluble NSPs) and in good nutrients absorption by facilitating gut motility (insoluble NSPs). Whereas, NSPs have various negative effects upon poultry like, viscosity is one that decreases digestion and passage rate results in less absorption of nutrients (Soluble). Moreover, NSPs trap nutrients that are in very high levels as non-soluble parts may cause inflammation of gut mucosa and may give way to secondary bacterial infections.
NSPs breakdown in practical poultry diets
The NSPs in poultry feed mostly comprises Arabinoxylans, Cellulose and beta glucans and occupies 50%, 25% and 5% respectively as of its total content. Arabinoxylans are the most abundant part of NSPs content in corn, wheat, barley & rye. Soybean is recognized for its diverse range of NSP contents.
Rice bran is rich in cellulose & Arabinoxylans. The typical Corn-SBM diet, containing 60% corn and 30% Soybean meal, is dominant at 43% arabinoxylans followed by cellulose at 27%, beta glucan at 2%. (Figure 2) Whereas, a typical wheat-SBM broiler diet, containing 60% wheat and 30% soybean meal, comprises arabinoxylan continues to dominate at 47%, followed by cellulose at 23% and beta glucans at 5% (Figure 3). In both types of diet, other parts as an individual either have very low nutritional significance or may not be cost effective. Moreover, cellulose is not a practical target for improvement in poultry. Therefore, Arabinoxylan is the most prevalent one and should be targeted to ensure maximum output in terms of nutrition, cost minimization & maintenance of good health in poultry operation.
Practical aspect of NSP utilization in poultry operation
This is scientifically proven that using exogenous enzymes to utilize NSPs brings significant benefits in poultry operation, but all are not best suited for all types of diets. This is because of a vast variation in NSPs contents in different feedstuffs and into the diet made by these. For example, Corn-SBM diet, mostly used in commercial poultry diet formulation in Bangladesh, differs from the wheat-SBM diet in aspect of NSPs content. Thus, the focus definitely should be paid accordingly to get optimum results. Xylan exists in diet as a very long chain polymer with a lot of sugars linked together. This long chain can include arabinose, as branched units. Highly branched xylan has a less capacity to bind cellulose, making it more soluble. Digesta becomes very viscous because of this soluble xylan and this decreases the passage rate, feed intake, and nutrient digestibility. Less branched xylan has to bind cellulose remarkably making it more insoluble. This makes it very rigid to be broken down and release of nutrients (Figure 4). As arabinoxylan is the most prevalent type of NSP in practical broiler diets, xylanase is by far the most efficient and cost-effective enzyme for improving NSP digestibility. Inclusion of only high-quality xylanase enzyme feed additives will make a significant contribution in cost minimization by release of the greatest amount of encapsulated nutrients and contributes to better poultry health management.
Moreover, corn contains mainly insoluble xylan (98%) that have very less branching and requires enzymes that are capable to target insoluble xylans efficiently as well as soluble one. GH10 primarily hydrolyzes soluble xylans, whereas the GH11 xylanase is of that kind which can dedicatedly target both insoluble & soluble xylans. Therefore, to maximizes the release of nutrients from a diet containing a high number of insoluble xylans and to reduce the effect of viscosity as well, the use of GH11 type Xylanase in feed formulation demands to be the foremost practical.