Phosphorus is an important mineral in the poultry diet,which is a component of organic compounds involved in energy, carbohydrate, amino acid and fat metabolism, nervous tissue metabolism, blood chemistry and lipid transport. Phosphorus functions as a constituent of bone.The requirement of phosphorus in birds can be affected by environmental conditions, genetic strains and other nutrients in the diet.Chicks and grower birds require more phosphorus than layers, because of the phosphorus needsfor skeletal growth.The laying birds require phosphorus for maintenance of skeleton, soft tissue and for egg production. Each egg contains approximately 80 to 120 mg phosphorus. Hence, the phosphorus requirement of laying hens varies depending on the rate of daily egg production. As the age advances, egg production decreases and the need for dietary phosphorus also decreases.
Total phosphorus is defined as the total mineral phosphorus in a ration,regardless of its availability to the laying hens. Available phosphorus is the portion of total phosphorus in the feed which is relatively available for absorption and utilization.Unavailable phosphorus is defined as that phosphorus which associates with phytate in the diet. Phytate is the major form of phosphorus found in cereal grains, beans and oilseed meal feed to poultry birds.Approximately 61-70% phosphorus is found in poultry diet ingredients, which is in the form of phytate phosphorus. Phytate is indigestible and an anti-nutritional factor. Poultry possess insufficient inherent phytase activity, so phytate phosphorus is partially available.Phytase is the requisite enzyme to degrade and release inorganic phosphorus.
Importance of Phosphorus
National Research Council (1984) recommended dietary phosphorus level for laying hens at0.32% available phosphorus per kilogram of diet.Low dietary phosphorus during the laying period can lead to increased incidence of cage layer fatigue, reduced bone ash, increased severity of osteoporosis and diminished bone strength. Phosphorus plays key role in carbohydrate metabolism, fat metabolism and the regulation of acid-base balance in body.
Deficiency of phosphorus, calcium or vitamin D, or all of these leads to lameness, stiff legs, ruffled feathers, reduction in growth, leg bones appear rubbery, joints become enlarged, poor egg shell quality, reduced egg production, thin shelled eggs, and shell less eggs. The phosphorous nutritional role relates to calcium. Hence, the absorption of these elements depends upon the ratio of dietary calcium to phosphorus. An excess of either can interfere this process and causes production losses. Excess calcium in the diet leads to the formation of calcium phytate complexes, which are highly insoluble and poorly digested.
Digestibility of Phosphorus
Table-1: Content and Digestibility of Phosphorous (P) in different Raw Materials.
Phytate (or) Phytic Acid Structure
Phytic acid is a complex of calcium (Ca) or magnesium (Mg) with myo-inositol,whichis an essential component of all seeds. Phytic acid is an anti-nutritional factor, whichbinds with phosphorus and other important nutrients, thereby decreasing their availability. Low availability of phytate phosphorus in poultry results in the excretion of large amounts of phosphorus into the nature which causes environmental pollution.
Figure-1: Structure of Phytic acid.Sources of Phosphorus and its Content
Dicalcium phosphate (DCP), Monocalcium phosphate (MCP),Defluorinated phosphate (Rock), Meat and Bone meal, and Fish meal are some of the sources of phosphorous.
Plant materials: Corn grain, wheat grain, wheat bran, broken rice grain, rice polish, groundnut meal, soya extract, sunflower solvent extract, bajra grain, and barley grains, etc., are the plant sources for phosphorus. The phosphorus content of typically used plant materials ranges from 0.09% to 1.09%. As this is largely in phytate form, its digestibility varies from 27% to 66% in poultry.
Animal sources: The total phosphorus content is as much as 30%. The amount of available phosphorus provided by animal sources like meat, fish, and bone meal varies from 59% to 74% depending on the material’s origin and production process. These sources run a greater risk of possible contamination.
Inorganic sources: High quality inorganic phosphates offer the combination of a consistently high total phosphorus content and excellent digestibility, and therefore widely used as a supplemental phosphorus.
Rock phosphate: Rock phosphate cannot be used directly in animal feed as the phosphorous content in it cannot be metabolized by animals. Rock phosphate contains impurities such as fluorine, cadmium and arsenic which should be removed during production process.It must be chemically treated, so that the phosphorus it contains change into the digestible orthophosphate form. Rock phosphate contains about 75% tricalcium phosphate, and 17% phosphorus and 34% calcium. Usage of rock phosphate shouldensure that it had less than 0.5% fluorine.
Dicalcium phosphate (DCP):Rock phosphate is digested with sulphuricacid, yielding phosphoric acid. After filtration, purification and defluorination, this feed grade phosphoric acid is reacted with quick lime or limestone. Thus, anhydrous dicalcium phosphate (DCP) is formed. DCPis used as the main source of phosphorus and calcium,which contains 18.5% phosphorus and 22% calcium. DCP strengthens the skeleton and accelerate birds’ growth.
Monocalcium phosphate (MCP): MCP is produced by reacting the DCP with purified feed grade phosphoric acid mono and dicalcium phosphate (MDCP). It will increase the phosphorus content of the product.MCP contains 22.8% phosphorus and 17%calcium.
Phytase releases the phosphorus bound in phytate molecule, increasing the availability/digestibility of this mineral to the poultry. When phytase act on the phytate molecule, they increase the solubility of phytate while reducing its antinutritional effect. Phytate is an anti-nutrient, whichincreases the mucin production and loss of amino acids, altering patterns of sodium secretion into the gut, and influencing the absorption of minerals. Phytase improves gut health as indicated by reduced secretions from gastrointestinal tract (GIT),which consequently improves the efficiency of energy utilization. Efficacy of phytase supplementation is dependent on microbial source, form of enzyme, temperature and pH optima of the enzyme, diet mineral concentration such as calcium (Ca), iron (Fe), magnesium (Mg), copper (Cu) and zinc (Zn), form of diet like pellet or mash or liquid, and disease status of birds, etc.
Phytase activity is measured in terms of inorganic phosphorus released from phytic acid and the activity is known as phytase unit (FYT). One phytase unit is the amount of enzyme needed to release 1 micromole of inorganic phosphate per minute from 5.1mM sodium phytate at pH 5.5 and 37°C. The main sites of phytase activity occurs in crop and proventriculus in poultry. In chicken, 69 to 86% microbial phytase activity is observed in the crop and 31 to 38% in the proventriculus. Supplementation of phytase in the poultry feed by replacing DCP using matrix value of phytase will save the feed cost.
There are two types of phytase available,namely 3 phytase and 6 phytase. The 3 phytase initiates the dephosphorylation of phytic acid at position 3 on the inositol ring of phytic acid. Whereas, 6 phytase initiates the dephosphorylation of phytic acid at position 6 on the inositol ring of phytic acid.PHYGEST™ HT is an intrinsically thermostable phytase enzyme of bacterial origin having 10,000 FTU/g at the dose rate of 100g per MT of feed. It can efficiently degrade IP6 of phytic acid to release bound myo-inositol.
Phytic acid binds with essential minerals like calcium, zinc and copper, and protein by its chelating potential and make them unavailable for absorption. By hydrolyzing the phytic acid to inositol and inorganic phosphorus, phytase counteract the anti-nutritional effects of phytate. Phytase supplementation in layers improves bioavailability of phytate phosphorus resulting an increase in egg production, egg weight and egg shell thickness. Phosphorus,which is one of the costliest items in poultry feed,when replaced in feed as inorganic phosphorus form by phytase enzyme result in better economic poultry production.By using PHYGEST™ HT, farmers will benefit economically and through performance of birds.
Notes: References available on request.
by Dr. S.R. Prabakar, Kemin Industries South Asia Private Limited