Feed accounts for more than 70% of production cost in poultry industry, hence its maximum utilization is of utmost importance for cost effective poultry production. All animals produce digestive enzymes in gastrointestinal tract which help in efficient digestion of feed. However, some of the enzymes are not produced in sufficient quantities for the complete digestion of dietary nutrients in poultry. Plants contain some compounds that either the animal cannot digest or which hinder its digestive system, often because animal cannot produce the necessary enzyme to digest these compounds. Almost 15-20% of feed is wasted due to lack of specific digestive enzymes in the GIT of animals and birds. In plant based raw material, phytates and indigestible fibre/non starch polysaccharides (NSPs) are present in significant amounts, which lower the nutritive value of feed. Besides, these also impair digestive functions, through binding with other nutrients, excess production of mucin, increased gut viscosity and faster feed passage from GI tract. To ameliorate these adverse effects, feed enzymes are added in poultry feed to improve its nutritive value, reduce cost of production and environmental pollution.
Exogenous enzymes
Energy is the most expensive component of feed, followed by protein and phosphorus. To extract maximum of these nutrient from raw material, it is necessary to use exogenous enzymes. There are two main indigestible nutrients in raw materials (corn, barley, wheat, sorghum, soybean meal, rapeseed etc.) and poultry feed, that is phytate bound phosphorus and non-starch polysaccharides (NSP) (Table 1 & 2). Not only are these costly ingredients not being utilized, they also cause detrimental effects in the gut. Hence use of phytase and NSP degrading enzyme (NSPase) is of prime importance.
Less-digestible comparatively cheaper ingredients such as agro based by-products from the food and biofuels industries can be effectively used with supplementation of fiber digesting enzymes. Similarly, addition of phytase reduces use of dicalcium / monocalcium phosphates (an expensive source of phosphorus). If alternate protein sources are used to replace soybean meal, then protease has important role to degrade indigestible proteins.
Non starch Polysaccharides (NSP):
Cereals, like corn, sorghum, bajara, barley, wheat etc contain a major NSP fraction arabinoxylan (AX) which accounts for 5-10% (dry matter basis) in cereal grain. The non-cellulosic polysaccharides consist of arabinoxylans and β-glucans, whereas arabinans, arabinogalactans, galactans, galactomannans, mannans, and pectic polysaccharides predominate in oil seed meal (soybean and rapeseed). AX has two fractions water soluble (causes a direct increase in the viscosity of digesta, visually causing problems such as wet litter) and insoluble (reduce nutrient digestibility). Both soluble and insoluble AXs are susceptible to degradation by endo-xylanases.
Phytate Phosphorus: Plant based feed raw materials contain 70% of phosphorus in bound form (phytate P) which is not available for the birds (Table 2). Besides reducing availability of phosphorus, it chelates other minerals (Ca, Zn, Na etc.) as well. Phytate, itself acts as anti-nutrient by increasing mucin production due to gastric irritation and increases losses of dietary nutrients (proteins and carbohydrates) and perhaps pancreatic enzymes. Phytase can help to increase phosphorus availability and reduction in anti-nutritional effects of phytate.
Enzymes
Phytase, Carbohydrases and Protease are the major enzymes being used in animal feed to improve digestion of phytate phosphorus, non-starch polysaccharide and protein respectively. In the past five years, the market for poultry enzymes has changed significantly with phytase, followed by xylanases and others. Other enzymes like amylases, proteases and mannanases are being used by few poultry producers. Enzymes are derived from microorganisms like bacteria (eg. Bacillus subtilis, E. coli and B. stearothermophils), fungi (Triochoderma, Asperigillus) and yeast (S. cerevisiae); these are carefully selected to substrate specificity and cultured under controlled conditions.
Application of enzymes in poultry feed
Enzymes can be used in following ways in poultry feed:
Use of matrix values to reduce the costly raw material, the matrix values quantify the extent to which nutrients are released by using the enzyme. Using matrix values one can reformulate the feed and reduce the quantity of costly ingredients for energy, protein and minerals.
Addition of enzyme to the standard feed formulation achieves improved bird performance (feed conversion ratio, egg production).
Enzyme usage gets better return on investment(ROI) through improved performance for example reduction in FCR, better weight gain, reduction in days to market weight etc.
NSP enzyme (Xylanase & beta-glucanase)
NSPase reduces nutrient encapsulating effect of the plant cell wall and break down the long chain soluble NSPs (particularly arabinoxylans and mixed linked beta-glucans). It improves the access of feed materials to digestive enzymes of the bird, the former by exposing nutrients such as starch and protein stored within plant cells, latter by enabling free movement of digestive enzymes and subsequent end product of digestion within the gut.
Arabinoxylan (AX) is the major NSP in poultry diets (>45%), hence use of high quality xylanase releases maximum of encapsulated nutrients from plant cell wall. Followed by AX, cellulose contributes about 25% of total NSPs but no enzyme system currently exists that can release complete glucose from cellulose in an efficient and economic manner (within a digestion period of less than 3 hours in birds). Other NSPs (mannan, galactan, pectin etc) are present in very small quantity(each <5%), hence it is practically unviable to use these enzymes.
In corn-soya based poultry diet, good quality xylanase is the most efficient and cost-effective enzyme to improve digestibility of non-starch polysaccharides.
It has been scientifically proved that specific short-chain oligosaccharides (can be termed xylooligosaccharides, XOS) produced by certain xylanases has positive effect on bird performance by promoting growth of beneficial microbes (lactobacilli & bifidobacteria) and reducing potential pathogens (Fig.1)
Very few commercial NSP enzyme products are purified enzyme protein otherwise the majority contains other materials, such as carrier or by-products of manufacture, which often contributes additional side enzymes activities. Hence, while considering multi-enzyme dosing, it is important not to attribute performance benefits to specific enzyme activities unless a clear mode of action is identified, such side activities may be at very low levels, or insufficiently thermostable to survive feed processing, and any effect they do have might be superfluous or even detrimental.
Phytase
Phytase is the requisite enzyme for degradation of phytate (myo-inositol hexaphosphate, IP6) and liberation of phytate-bound phosphorus (phytate-P). Phytase is the largest selling enzyme worldwide. Most of the poultry feed millers use phytase to improve phosphorus digestibility, as this is a limiting enzyme in monogastrics. With limitations in the use of animal proteins in some markets and due to pressure from fertiliser market, phosphate prices have increased significantly and use of inorganic phosphorus in poultry feed is costlier. Phytase has the potential both to enhance P digestibility and counteract the anti-nutritive properties of phytate, ‘extraphosphoric’ effects of phytase. It can significantly reduce the dependence on inorganic phosphorus source (DCP/MCP). It has been added to monogastric diets for more than a decade.
The primary goal and mode of action of phytase is to reduce phosphorus excretion and cost savings in the diet. Use of fungal or first generation phytase is limited and considered to release phytin bound phosphorus. However, advent of new generation bacterial phytase helps to increase retention of calcium, energy and amino acids as well. Therefore, the economic benefit of phytase is quite attractive.
Conclusions
Least cost feed formulation without hampering the performance is a major goal for poultry feed millers and integrators. Enzymes are proven and accepted feed supplements for more than a decade. Besides increasing digestion of dietary nutrients, it also help to reduce the anti-nutritional effect of indigestible constituents. By far phytase and xylanase are more consistent in delivering maximum return on investment. Choosing best enzymes in terms of gastric stability, thermostabiity and potential to release maximum nutrients is of most important.
References are available on request
by Dr. Kumar Kore, AB Vista
