Phosphorus is a critical nutrient required by all animals. The main role of phosphorus is to support skeletal formation, mainly bones and teeth. Nearly 80% of the body’s phosphorus is contained in the bone. Phosphorus also plays a key role in carbohydrate metabolism, fat metabolism, lean tissue deposition, and as a component of phospholipids, which are important for proper cell structure.
Table 1 shows the phosphorus content of typical ingredients used in poultry and swine feeds. Plant-based ingredients like corn, wheat, soybean meal, wheat middlings, and Distiller’s Dried Grains with Solubles (DDGS) are fairly low in phosphorus content. A typical combination of corn and soybean meal (the most common ingredients used in poultry and swine feeds) will provide less than half of animal’s requirement of phosphorus.
|Table 1. Phosphorus Composition of Ingredients Used in Poultry and Swine Feeds|
|Ingredient||Total Phosphorus %|
|Distiller’s Dried Grains with Solubles (DDGS)||0.69|
|Meat and Bone Meal||4.63|
|Source: National Swine Nutrition Guide, 2010|
Animal byproducts such as meat and bone meal and poultry byproduct meal contain much higher levels of phosphorus than the plant based ingredients and can be important sources of phosphorus in animal feeds. Dicalcium phosphate, an inorganic phosphorus source, contains a high level of phosphorus compared to plant and animal based ingredients. However, due to cost, inorganic phosphorus sources are typically only included in the diet at levels to fill the gap between the animal’s phosphorus requirement and the level of phosphorus provided by other dietary ingredients.
Unfortunately, not all of the phosphorus in feed ingredients is available to animals for productive purposes. In grains and seeds, this is due to phytate. Phytate is a complex molecule that binds phosphorus (and other nutrients) for storage in seeds and grains. Between 60 to 70% of phosphorus in plant based ingredients occurs as phytate bound phosphorus. This phytate bound phosphorus is unavailable to the animal, because the digestive tract lacks adequate amounts of the enzyme (phytase) necessary to release the phosphorus from the phytate complex.
Phytase is an enzyme capable of releasing phosphorus from the phytate complex in grains and seeds. This phytase is a specific, commercially-available phytase product added to the diet to release phosphorus. Any phosphorus released by phytase from ingredients is then available for use by the animal to meet phosphorus requirements and to be used for productive purposes.
Phytase activity is typically expressed as “phytase units” or “FTU” per unit of feed. In general, 500 FTU of phytase per kilogram of feed liberates 0.10% phosphorus from dietary ingredients. In addition, this level of phytase also liberates calcium and other nutrients bound to the phytate molecule.
Table 2 shows a comparison of a swine grow-finish diet formulated with and without phytase. The addition of phytase decreases the amount of supplemental phosphorus (dicalcium phosphate) required to be added to the diet. In addition, the amount of supplemental protein (soybean meal) is also reduced.
|Table 2. Comparison of a Swine Diet With or Without Phytase|
|Soybean Meal, %||10.00||10.00||–|
|Dicalcium Phosphate, %||0.60||0.05||-0.55|
|Total Phosphorus, %||0.50||0.40||-0.10|
|Available Phosphorus, %||0.25||0.25||–|
|Feed Cost, $/ton||$342.07||$333.79||-$4.28|
The total amount of phosphorus in the diet is decreased 0.10% (0.50 to 0.40%). However, the amount of available phosphorus (the amount of phosphorus available to the animal for productive purposes) is the equal between the diets. This is because we are making more of the phosphorus from dietary ingredients “available” when phytase is added to the diet. In addition, feed cost is substantially decreased due to the competitiveness between suppliers of commercially-available phytase and the high cost of inorganic phosphorus supplements.
One major advantage of using dietary phytase is reduced phosphorus excretion.
One major advantage of using dietary phytase is reduced phosphorus excretion. The phytase containing diet in Table 2 indicates total phosphorus in the diet can be reduced 0.10% with less inorganic phosphorus supplementation. This reduction in total phosphorus in the diet results in a similar reduction in the amount of phosphorus excreted by the pig (phosphorus not used by the pig).
Table 3 demonstrates the effect of using phytase on phosphorus excretion. Experimentally, daily phosphorus intake was equalized between pigs fed diets with and without phytase (not done practically), the digestibility of phosphorus was increased nearly 11% when phytase was added to the diet. The addition of dietary phytase decreases the amount of phosphorus excreted through the feces by approximately 17%.
|Table 3. Effect of Phytase on Phosphorus Excretion|
|Item||No Phytase||Phytase||Change, %|
|Phosphorus Intake, g/day||5.58||5.58||–|
|Fecal Phosphorus, g/day||3.70||3.07||-17.0|
|Urine Phosphorus, g/day||0.07||0.07||–|
|Total Excreted Phosphorus, g/day||376||3.14||-16.5|
|Digested Phosphorus, %||34.1||44.9||+10.8|
|Source: Hill et al., 2008|
The decrease in phosphorus excretion determined experimentally has also been evaluated on a practical basis. Table 4 illustrates the effect of reduced phosphorus diets on total manure phosphorus excretion and the amount of land required to manage the level of phosphorus. The ability to reduce phosphorus level through the use of phytase resulted in a 31% reduction in phosphorus excreted. This resulted in a reduction in the amount of land required to handle the phosphorus excretion in the two types of manure storage systems analyzed.
|Table 4. Manure Phosphorus Excretion and Land Required to Manage Excretion in a 1,000 Head Capacity Pig Finishing Building|
|Normal Corn-SBM||Reduced Phosophorus|
|Manure Stored and Incorporated||13,000||8,900|
|Land Required, Acres||257||177|
|Anaerobic Lagoon and Pivot Irrigation|
|Phosphorus Excretion, lb P205/year||13,000||8,900|
|Land Required, Acres||90||62|
|Source: Reese and Koelsch, 1999|
In summary, phosphorus is a critical nutrient required by poultry and swine. Unfortunately, a significant portion of the phosphorus in typical ingredients is unavailable for productive use by animals due to the phytate complex. The use of dietary phytase releases previously unavailable phosphorus, reduces the amount of supplemental phosphorus, and reduces feed costs. In addition, phosphorus excretion and the amount of land required to handle excreted phosphorus is reduced when phytase is added to poultry and swine feeds.
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