Role of Individual Enzymes in Poultry Nutrition
The use of enzymes in poultry nutrition has great importance. The use of exogenous feed enzymes in poultry diet is becoming a norm to overcome the adverse effects of anti-nutritional factors and improve digestion of dietary components and bird performance. In poultry, feed is accounting up to 70% of total production cost. Consistent increase in the price of feed ingredients has been a major constraint in most of the developing countries like India. As a consequence, cheaper and non-conventional feed ingredients have to be used which contain higher percentage of NSP’s along with starch. Poultry naturally produces enzymes to aid the digestion of feed nutrients. However, they do not have enzyme to break down fibre completely and hydrolysis of non-starch polysaccharides (NSP) present in the cell wall of the grains. They need exogenous enzymes in feed to aid digestion.
Enzymes are biological catalyst composed of amino acids with vitamins and minerals. They bring about biochemical reactions without themselves undergoing any change. The benefits of using enzymes in poultry diets include not only enhanced bird performance and feed conversion but also less environmental problems due to reduced output of excreta.
No common feed ingredient is digested 100% in the animals’ gastrointestinal (GI) tract. Although the digestive system is amazingly efficient at breaking down ingested food to its basic components by means of chemical and mechanical action, sometimes the inherent systems need a little “boost” in capability. In order to properly select the enzyme desired for a specific outcome, one needs to understand the concept of a substrate, as this is one of the most important factors required to successfully employ an enzyme regime in your nutritional program. A “substrate” is the portion of the feed that the enzyme will break down to release the nutrients bound to it. It is similar to a “lock and key” concept, where the substrate is the lock, and the enzyme is the key. If there is no lock, then it becomes absolutely pointless to buy a key! Therefore, it is important to consider what substrates (i.e. ingredients) are prevalent in your diets to best determine which enzyme(s) you should include for optimal results.
Types of Enzyme Available for Poultry:
In the field of nutrition and applied feeding programs, one area in which producers have adopted improved technology is the use of feed enzymes including proteases, phytases, lipases and carbohydrases such as amylase, beta-glucanase and xylanase (Khattak et al., 2006). The use of feed enzymes to improve starch digestibility are, of course, much more recent and is common especially for improving the digestibility of grains such as wheat, barley and rye (Choct, 2001). Recently, considerable interest has been shown in the use of phytase as a feed additive, as it not only increases the availability of phosphate in plants but also reduces environmental pollution.
These feed enzymes can be marketed as single enzyme inclusions or as mixtures or cocktails of carbohydrate-degrading enzymes or even in combination with protein and/or phytate degrading enzymes. These carbohydrate-degrading enzymes cocktails are generally marketed with an energy replacement value, and sometimes with amino acid replace values if cell-wall degradation and release of bound protein is targeted with the enzyme cocktail.
How NSP Compounds Effect the Growth of Bird:
- Endogenous enzymes of poultry can not digest the NSP compounds which are present in the feed
- The digestibility of feed by birds decreases
- As the bird cannot break the cell wall components the other useful and digestible components are also lost as they are entrapped by NSP components
- The intake of feed increases, the utilization of feed by the birds decrease and cost increases
- The food which is taken by bird is not digested and the intestinal viscosity increases
- Absorption of bile juices increases, microbial flora of intestine gets altered and its growth increases
- The competition between microbial flora and the bird increases for the nutrition
- The sticky dropping of undigested feed is observed as the feed is not completely utilized and it absorbs high amount of water
- Increased rate of mixing of bile, pancreatic and intestinal secretions with digesta increases the viscosity and increases the amount of sticky dropping
- As this feed is not completely utilized, this feed is not expelled out and because of this the passage tract is blocked and the intake of feed decreases
- As the feed intake is high and endogenous enzyme do get excreted out
- The loss of endogenous enzymes is observed
- Reduction of nutrient availability is observed in birds and the distortion of growth and feed conversion
- As the viscosity of the dropping is high the eggs are dirty
- It effects environment by high nitrogen and phosphorus exertion as the feed is not completely digested
Poultry Feed Enzymes-Mode of Action:
Enzymes targeting corn soya diets were introduced many years ago to target several substrate components within the plant material including fibre, starch and some plant proteins.
It is thought that NSP enzymes function through a composite of three separate activities, the contribution of such activity varying with ingredients and individual birds. The two main key functions for a corn soya based diet would be plant (cereal) cell wall destruction, and stimulation of beneficial bacteria with changes in the fiber composition.
Cell wall destruction: encapsulation of nutrients:
The cell wall material in the starchy endosperm of corn and sorghum is constructed mainly of small amounts of cellulose encrusted with hemicellulose, the bulk of which is arabinoxylan with min/or beta glucan components and lesser contents of mannans (Stone, 2004). Since poultry do not possess the necessary enzymatic capacity to degrade plant cell walls, a lot of the content (especially starch and protein) within this material can effectively bypass digestion or not be broken down until the lower gut by bacteria. This factor of encapsulation is based on the fact that some endosperm cells in corn and other ingredients manage to avoid physical breakdown during the activities of grinding and pelleting in feed manufacturing, and gizzard activity.
Effective degradation of this material requires the addition of sufficient amounts of the appropriate NSP enzyme activity such that ‘holes’ are created in the cell wall. This allows water hydration and large enough amounts of pancreatic proteases and amylase enabling better digestion of the starch and protein more rapidly. Xylanase, and to a lesser extent cellulases (beta-1,4glucanases) have proven most effective in the field (Zanella et al., 2004; Leslie et al., 2007). Mannanases and pectinases have targeted the soya more so than the corn fraction of the diet, but with the same endpoint in mind (Jackson et al., 2004).
However, in a corn soya based diet, one will need to use NSP enzymes, i.e. Xylanase, glucanase, that are more effective at targeting and breaking down the insoluble fibre fraction. A direct benefit of feeding these enzyme products is through reducing the variability in birds and improvements in bird uniformity across the different feed batches.
Bacterial population stimulation:
Exogenous NSPases break down plant cell wall carbohydrates and reduce chain length producing smaller polymers and oligomers. At some point, the fragments become small enough, i.e. Short chain oligosaccharides, and numerous enough to act as a substrate (prebiotic) for bacterial fermentation.
Xylanase, mannanases and cellulases produce xylo, manno or glucooligosaccharides, respectively. The benefit of such end products depends upon the type and quantity of the oligosaccharides produced, with different enzymes producing different oligosaccharides. These short chain oligosaccharides travel to the lower gut and become substrates for bacterial fermentation in the ileum and caecum, which can be beneficial with VFA production and altering the bacterial population.
Role of Individual Enzymes in Poultry Digestion:
Break down non-starch polysaccharides (NSPs), including soluble and insoluble arabinoxylans, in the fibre fraction of plant cell walls as well as reducing digesta viscosity and improving digestibility, nutrient release and feed passage rates. This ‘door opening effect’ makes cell components more accessible by other enzymes. Xylanase hydrolyse 1,4-beta-D-xylosidic linkages of hemicellulose.
Main Function of Xylanase:
- Break down the soluble fiber (xylose) and opens up feed stuff cell walls
- Breaks insoluble fiber into smaller particles resulting in increased lower gut fermentation
- Reduces gut viscosity and wet litter
- Releases some energy and a small amount of protein
Mainly for high soybean meal formulas. SBM has 40% of its carbohydrates that are indigestible. This causes a viscous material in the gut that may lead to loose drops in the bird and wet floors. This is probably part of the anti-nutritional effects of SBM.
Main function of Alpha Galactosidase:
- Breaks down the soluble fiber
- Makes more digestible nutrients including carbohydrates available to the bird
- Reduces the viscosity of the gut and incidences of wet litter
- Reduces production cost
β-Mannan is an anti-nutritive fiber found in soybean meal. β-Mannan looks like an invading pathogen.
Main Functions of β-Mannanase:
- Breaks down the β-Mannan
- Prevents the immune response
- Spares the protein and energy
- Improves growth and feed efficiency
Acts on starch, increasing its hydrolysis and thereby improving its digestibility by hydrolysis of 1,4 glucosidic linkages. Its actions complement the secretion of endogenous amylase by the bird, freeing up energy to fuel growth. Increasing starch digestibility also reduces the presence of glucose as a potential substrate for non-beneficial bacteria in the latter part of the GIT.
Increases protein digestibility through hydrolysis of storage and structural proteins, and disrupts interactions of proteins with starch and fibre in the diet. Additionally, they target other antinutritional factors in the diet e.g. residual trypsin inhibitors and lectins in soybean meal and some other vegetable proteins, thereby improving nutrient digestibility.
What does a protease do?
- Breaks peptide bonds between amino acids
- Endogenous proteases like trypsin and pepsin have very specific functions in digestion
- Exogenous proteases are more broad spectrum
Lipase: Increases the fat digestibility by its hydrolysis and thereby improving its digestibility.
Xylanase, Amylase, and Protease:
These cocktail enzymes are produced using microbial source. The microbial sources used are selected in such a way that they not only produce the enzyme but also act as Probiotics for birds.
Phosphorous is a key nutritional requirement for poultry to provide bone growth. Most of the phosphorus contained in animal feed of plant origin exists in the storage form phytate. Poultry can not digest phosphorus contained within phytate, since they lack phytase enzyme that breaks down this phytate molecule. Therefor the inclusion of the phytase enzyme in poultry feed is required for release of phytate bound phosphorus.
Breaks down fibre. Degrades β-glucan by cleaving β-1,3(4) glucosidic linkages
Breaks down indigestible pectin. Reduces digestive viscosity. Degrades pectin α-1,4- linked anhydrogalacuronic acid.
Addition of enzymes to feed functions in various ways in birds body thus improving its nutrients utilization and overall performance:
By reducing the gut viscosity:
- Cereals contain high proportions of their energy in the form of non-starch polylsaccharides.
- Cereals contain soluble indigestible polysaccharides like arabinoxylan (wheat), mixed linked –
glucans (in barley and rye), lignin, limit dextrin, antinutritional factors like phytic acid and
- These NSP are able to bind large amount of water – increasing viscosity in the gut – affects rate of
passage of digesta – rate of mixing of bile, pancreatic and intestinal secretions with digesta -rate of
absorption of digesta – increases the amount of sticky droppings.
Addition of suitable multienzyme preparation improves birds performance in following ways:
Increasing the effectiveness of host (endogenous) enzymes:
- Breaking down the gel form characteristic of soluble fibres allows the birds digestive enzyme to function more efficiently. This improves starch, protein, fat, amino acids and energy digestibility.
Alteration in feed passage rate:
- The enzymes reduce the water holding capacity of the gut contents thus increasing the dry matter content stimulating feed intake.
Effect on excreta characteristics:
- Addition of enzymes also reduces the dry matter outside the body thus has marked impact on excreta volume and composition. Due to protein digestibility lowering of excreta output is observed.
Effect on litter problems:
- Reduced viscosity improves nutrient digestion, lower water intake and help to reduce litter problems.
Release of nutrients:
- Enzymatic depolymerization renders the NSP free releasing nutrients in the gut and it available to the animal.
- Starch masked by cell structure is released leading to increase in metabolisable energy.
- Proteins are also released by action of proteases. This release leads to maximum absorption of minerals and results in improvement in nutrient utilization.
Availability of phosphorus:
- Cereals and oilseeds contain 1-2% of phytate, and 60-90% of total phosphorus present in the seeds in this phytate phosphorus.
- Phytase hydrolyses phytic acid to myoinositol and phosphoric acid in step wise manner forming myoinositol phosphatic intermediates (IP5, IP4, IP3, IP2, IP1).
|Phytase||Phytate||Release phosphorous stored in phytate||1) Improve FCR|
2) Improve litter quality
3) Greater uniformity
4) Reduce feed costs
5) Use cheaper feeds
6) Reduce DCP use & costs
7) Reduce Phosphorous excreation
8) Reduce the mortality
9) Improve overall performance of birds
|Protease||Protien||Improve protein digestibility|
|Pectinase||NSP||Break down indigestible pectin. Reduce digestive viscosity|
|Xylanase||NSP||Break down fibre|
|Celluase||NSP||Break down fibre|
|Beta-Glucanase||NSP||Break down fibre|
|Alpha- Amylase||Starch||Improve starch digestibility|
|Lipase||Fat||Improve fat absorption|
- Poultry do not produce enzyme for the hydrolysis of non-starch polysaccharide present in the cell wall of the grains.
- Addition of exogenous enzymes specific for a given feed formulation will enhance the availability of feed components to the birds.
- Exogenous enzymes increase the energy by hydrolyzing the fibrous contents present in feed.
- Calcium and phosphorus precipitations are prevented and absorption of them is promoted by these enzymes.
- These exogenous enzymes complement endogenous enzymes in conditions like more stress and at the early age of the birds.
- The production of endogenous enzymes may be limiting in conditions like age, health, climatic conditions etc. At times these exogenous enzymes help digestion in birds
- Exogenous enzymes help bird to digest the NSP of cell wall.
- As the NSP components of cell wall breaks the other useful components which are entrapped also becomes available to the birds.
- The viscosity of the bird dropping decreases.
- There will be no loss of endogenous proteins.
- There will be reduced nitrogen and Phosphorus exertion.
- The starch in the cereals get unmasked as the cell wall breaks and the high amount of energy is produced to bird.
- The proteins are also utilized up to maximum extent and the maximum absorption of minerals and maximum utilization of feed nutrients is observed.
- The intake of feed and its utilization increases, intestinal flora is maintained properly.