The Role of Feed Enzymes in Poultry Nutrition
A.K. Panda, S.V. Rama Rao, M.V.L.N. Raju, M.R. Reddy and N.K. Praharaj
The competition between human and livestock population for the existing animal and plant resources has been of great concern to the poultry nutritionists. Today/ the poultry industry has already challenged by the high price of the feed ingredients. Moreover in the next century there will be a shortage of conventional feed stuffs for use in poultry production. Efforts are on to look forward for the new feed resources and to evaluate them for their inclusion in the poultry ration. However many of the feed stuffs are characterized by the presence of certain incriminating factors. The incorporation of feed stuffs containing incriminating factors may adversely affect the performance of poultry. The nutritional strategy involving the use of feed enzymes offer immense potential to overcome the problems.
The use of enzymes in feed mixtures of growing poultry particularly for young chicks has been the subject of much research activity in the recent decades. The interest in the feed enzymes is a reflection in changing the attitude of the society and the economic climate of the feed industry. It has been seen that approximately two billion tons of cereal grains and 140 million tons of legumes and oil seeds are produced through out the world each year (PAO, 1993) which yield an estimated 230 million tons of non starch polysaccharides (NSP) as a part of variety of products. The digestibility of NSF is very low in poultry and large amount is voided through the feaces. NSPs are able to bind large amounts of water and as a result of, the viscosity of the fluid increased. The increase in viscosity may cause problems in the small digestion of fat, protein and carbohydrate. In addition high viscosity of digest increases the amount of sticky droppings. These problems can be overcome by addition of enzymes to feed. An increased use of feed enzymes is expected not only from the aspect of economic gain but also from the environmental point of view, as enzymes .enhances nutrient utilization, there by reducing the manure out put and reducing nutrient excretion particularly excess phosphorus, nitrogen, copper and zinc.
Enzymes are biological catalyst which brings about biochemical reactions without themselves undergoing any change. Enzymes are protein in nature and composed of amino acid arranged in a sequence. Enzymes activity is dependent on the substrate in a random manner or at a very specific site on the substrate. They accelerate chemical reactions of the living cells for certain nutrients from feed stuffs to become available to the organs and tissues. Enzymes are not living organism but their product of living organism such as bacteria, yeast, fungi and plant tissue. Feed enzymes function by enhancing the digestibility of the feed nutrients in situ, Enzymes are involved in all anabolic and catabolic pathways of digestion.
Commercial feed enzymes are produced from naturally occurring fungi, yeast and bacteria. Mutant or genetically modified strains of microbes, producing excessive quantities of particular enzymes, are grown on sugar and starch hydrolyses substrates using modern fermentation technology. The enzymes produced are extracted and separated from the source of microbes. They are then stylized before being prepared as free flowing powders or liquids for mixing into feeds. Commercial enzymes used as feed supplements do not contain a singly enzyme but: rather they are preparations of a variety of enzymes. The enzymes used in poultry feed are mainly carbohydrates and when added to feed, become active after hydration by different commercial organizations. Some of die most common preparations available in the market are Novozyme Sp-243 containing beta glucanase, cellulose, pectinase and amylase; Selfeed containing protease, amylase, cellulose, lipase and pectinase;
Nutrizyme containing cellulose, B-glucosidase, hemicelluloses, pectinase, protease and amylase.
Ideal commercial enzymes should have
* Good self life in terms of storage stability.
* Show specificity of action.
* Good heat stability during the feed preparations.
* Uniform distribution in the feed.
* Less expensive and more safety. Advantages
* Maximizing the efficiency of conventional and non conventional feed stuffs.
* Increasing the digestibility of fiber components and rendering the nutrients more available for digestion, there by reducing the manure output.
* Reducing the affects of anti nutritional factors like tannins, saponins and goitrogen.
* Exploring the genetic potentiality of the bird, so as to enable them to more quantity of teed to achieve maximum growth and production.
* Reducing the early mortality due to the problems associated with harmful moulds and aflatoxin in poultry feeds.
* Allowing greater flexibility and accuracy in feed formulation, reducing the feed cost and maintaining the bird performance.
* Reducing environmental pollution by reducing nutrient excretion particularly excess phospliorus, nitrogen, copper and zinc.
Cell wall polysaccharides mainly consist of non starch polysaccharides (NSP) which are the recombinant anti nutritional factors (ANF'S) in the Feed. Besides, increasing the intestinal viscosity, NSP also increase the incidence of watery and sticky droppings in poultry. Some of the non starch polysaccharides found in the common feed stuff is given in Table 1.
Table 1. Resume of NSF found in the feed stuff
Arabinoxylans - It consists of back bone of xylose residues and are branched with Arab noses. These are the predominant ANFS present in cereals like wheat, rye and triticales.
Rye is unsuitable for poultry diets because of low feed conversion, reduced growth and large amount of sticky droppings. This is due to the water soluble fraction of the arabinoxylans present in it. The addition of xyianase to rye based diet will reduce the amounts of sticky droppings.
Pectin - The carbohydrates of pectin are galacturonic acid and ramose which constitute the back bone of pectin. Pectins like xylems also increase the viscosity of the digest. Use of pectinase gives the best results in diets containing legume like Soya, beans and peas.
p-glucanase - These are glucose polymers containing a mixture of pl-3 and pl-4 linkages which make their physiochemical properties totally different from cellulose which is a straight chain glucose polymer with only Bl-4 linkage. Barley and oats contains a high level of mixed linked p-glucanase (3-4%) which is responsible for its poor nutritive value in chickens. Barley also contains an appreciable amount of soluble non starch polysaccharides other than a glucanase. The negative effect of P-glucans in barley and oat can be alleviated by the use of dietary enzymes containing P-glucanase activity.
Galactosides - Addition of galactosidase will not improve the nutritional value of the feed but eliminate the anti nutritional value of a galactosidase which cause diarrhea and stomach problems.
Phytic acid - Phytic acid or phytate is a naturally occurring organic complex found in plants. As a reactive anions, it forms a wide variety of insoluble salts with divalent and trivalent cations. Fhytic acid is also known to form complexes with proteins and consequently reduce their availability. Because of lack of endogenous phytase, which hydrolyses phytic acid, phytic phosphorus is biologically less available to poultry. Phytic acid consists of a six carbon inositol ring with six phosphate groups which can be hydrolyzed by the enzyme phytase, produced by a number of microorganisms. If all the phosphate groups are cleaved by the enzyme/ it would release six phosphates. This molecule can bind with other cations like calcium, magnesium, zinc and iron. When these minerals are bound to the phytic acid they become unavailable to the system.
Supplementation of microbial phytase not only reduces the need for mineral supplementation by increasing the availability of cations (Phosphorus, calcium, nine and copper) bound to phytic acid, but also has, the potential impact to reduce environmental pollution by minimizing the excretion of phosphorus and nitrogen in manure.
A resume of enzymes used in poultry feed is given in Table2.
Table 2. Enzymes used in Poultry feeds
Performance of chickens to diet with enzyme supplementation
Poultry do not produce enzymes like cellulose, hemicelluloses, xylanase and B-glucanase which are required for the digestion of cell wall component of plant material. About 85-90% of poultry feed consists of plant materials which contain large amount of dietary fibers. The nutritional strategy involving the use of commercial feed enzymes offer the potential to overcome the problems. By carefully selecting the enzyme from the wide range of enzymes commercially available, improvement in the performance can be obtained in the poultry.
The most promising results with enzymes are in diets with wheat or barley as the main grain, because they both have non starch polysaccharides (NSP) in the cell walls and the anti nutritional activity can to some extent be eliminated by enzymes. The and nutritive effect of p-glucans in the gastrointestinal tract of young chicks can be eliminated by adding p-glucans of microbial origin to barley based diet, thus making it acceptable for broiler fattening diets. The addition of B-glucanase has allowed barley to be used as major ingredients in broiler diets and xylanase supplementation has been claimed to improve the economy of wheat based diets/ the litter condition and consequently welfare of the birds. The beneficial effect of enzymes in barley/oat, wheat and rye in diets is based on the hydrolysis of the viscous non starch polysaccharides. Improvement in live weight gain and feed conversion efficiency and reduced sticky dropping in broilers due to me inclusion of enzymes in the diet have reported by several workers (Raghavan, 1990; Arora et al 1991; Wenk, 1992). Dietary inclusion of 1.0 g Selfeed (protease 10,00,000 units amylase 7,500,000 units, cellulose 4,000,000 units, lipase 3,00,000 units and pectmase 2,00,000 units) per kg diet in the broiler revealed that there was a better gain in weight and feed conversion efficiency (Ramjane, 1992). Nahm and Karlson (1985), used cellulose obtained from Trichoderma viridae @ 0.008% in the broiler diets containing wheat bran at 0,10 and 20% levels and noted significant improvement in body weight gain and phosphorus availability. Supplementation of mufti enzymes in low, moderate and high fiber diets and the resultant performance of broilers were investigated by Nagalakshmi and Devegowda (1991). They found a significant improvement in body weight and feed conversion in low and high fiber diets and a reduction in the moisture content of droppings.
Increase intestinal viscosity is generally associated with reduced growth performance-Supplementation of wheat diets with an enzyme reduced gut content supernatant viscosity which was accompanied by improved performance ( Bedford , 1996). Feeding of certain grain and grain by products leads to incidence of sticky droppings. Wet dropping is a big problem especially in laying hens because of increase in percentage of dirty eggs. It may also increase gas production (i.e. ammonia), fly and rodent population in the shed. Supplementation of P-glucanase enzymes was found to be successful in reducing the adverse effect (hesslman and Amon, 1985).
Recently interest in the use of phytase as a feed additive concern over phosphates in animal wastes. Phytic acid is generally regarded as being resistant to hydrolysis in the avian gut because of lack of endogenous phytase. Unfortunately, many grains, oilseed meals and plant derived products contain high level of phytic acid, which in turn contains 60-80% of total phosphorus present the phosphorus contained in phytate is not available to poultry because they lack the enzymes needed to hydrolyze-e phytate.into inorganic phosphorus and inosilol. Besides being an indigestible constituents, the phytate phosphorus markedly reduced the bio-availability of several multivalent cations mainly calcium, manganese, zinc, ferrous and ferric iron by forming insoluble phytatemetal complexes. The use of exogenous phytase can significantly enhance phosphorus digestion through destruction of plant derived phytate.
There are several studies which indicate that microbial phytase supplementation increase the body weight gain and feed intake in broiler chickens (Den bow et al. 1995; Sebastian et al. (1996). Simons et al. (1990) reported that microbial phytase supplementation of low phosphorus maize-soybean diet increased the availability of phosphorus to over 60% and decreased the amount of phosphorus in the droppings by 50%. Palluf et al. (1992) found that phytase addition to the diet of pig increased the apparent absorption of Mg, Zn, Cu and Fe, respectively up to 13%, 13%, 7% and 9%.The poultry industry is becoming increasingly receptive to the use of supplemental enzymes. Addition of enzymes to the poultry diets has a positive response on the digestibility of feeds and leads to better performance. Besides, supplementation of enzymes can improve the productive value of commercial feeds and allow greater flexibility in feed formulation. It has also a potential impact to reduce the environmental pollution by minimizing the excretion of phosphorus and nitrogen in the manure.