Phosphorus contributes the greatest single mineral ingredient cost to swine diets. Pigs require phosphorus for:

• Skeletal and teeth formation

• Lean muscle deposition

• Synthesis of milk components

• Carbohydrate metabolism · Lipid transportation

• Production of adenosine tri-phosphate (ATP), the primary source of metabolic energy

Environmental Phosphorus Concern
The development and implementation of Nutrient Management Plans, matching land application of manure to crop requirements, continue to be monitored at local and national levels. For numerous years, the only nutrient routinely measured for land application was nitrogen. Due to environmental and economical factors, phosphorus has come under close scrutiny in Nutrient Management Plans. Excessive phosphorus levels in soil can occur when manure phosphorus levels applied to land exceed plant requirements. However, in some areas low phosphorus is a concern, and livestock manure is an alternative to inorganic phosphorus sources. It is important that soil analysis be routinely conducted to ensure proper application rates.

Commonly held production goals are to reduce feed cost and soil phosphorus levels while maintaining/improving growth characteristics and carcass performance. Unfortunately, most of the phosphorus in commonly used cereal grains is concentrated in the seed coat as phytic acid (phytate). Phosphorus, in the form of phytate, is very low in bioavailability to swine (Table 1).
 

Table 1  Total and Available Phosphorus Content of Common Feedstuffs Used in Swine Diets
Feedstuff	Total Phosphorus, %	Bio-Available Phosphorus, %	Absorption, % of Total Phosphorus
Corn	0.26	0.08	30.77
Grain Sorghum	0.31	0.09	29.03
Oats	0.34	0.15	44.12
Soybean Meal	0.61	0.24	39.34
Wheat	0.30	0.09	30.00
Wheat Midds	0.47	0.12	25.53
Source: Modified from Nelsen et al.

Environmental Phosphorus Solution
Reducing soil phosphorus levels via dietary manipulation can help ease environmental phosphorus concerns. The incorporation of the microbial enzyme phytase into swine diets increases availability of phytate-bound phosphorus from grains and oil-seeds. Approximately 66% of the phosphorus in corn and 61% of the phosphorus in soybean meal is bound in the phytate form. Use of the phytase enzyme in swine diets can:

• Increase availability of phosphorus contained in cereal grains, thereby reducing the amount of supplemental phosphorus needed and total phosphorus level in diets.

• Reduce the amount of excreted phosphorus, which in turn, lowers phosphorus levels applied to land via manure application.

Using phytase in swine rations increases bioavailability of phytate-bound phosphorus, which enables the dietary phosphorus level to be lowered. Thus, less supplemental phosphorus is needed, which lowers phosphorus cost. The use of microbial phytase in swine growing and finishing diets can reduce phosphorus excretion 20-25% by increasing digestibility of phytate phosphorus and reducing use of inorganic phosphorus sources (Virginia Polytechnic University and University of Kentucky). The excretion of phosphorus was reduced from 7.49 to 4.49 g/d by feeding a diet containing phytase (University of Kentucky). This resulted in phosphorus digestibilities of 51 and 35.4% for diets with and without microbial phytase, respectively. Diets containing phytase were 0.1% lower in total calcium and phosphorus than controls. ADM Alliance Nutrition Research reported that adding 500 FYT/kg of phytase improved digestibility and net phosphorus utilization by 33.76% and 41.6%, respectively, as compared to negative control diet that did not contain phytase (Table 2).
 

Table 2 Effect of Phytase on Phosphorus Digestibility and Excretion (110 lb Pigs)
	Positive Control	Negative Control	Phytase
Available Phosphorus Phytase, FYT/kg Number of Pigs	0.31 0 4	0.10 0 4	0.10 500 4
Phosphorus (P) Metabolism P intake, g/d Total P excretion, g/d         Fecal P, g/d Urine P, g/d       Digested P, g/d P Digestibility, % Retained P, g/d Net P Utilization, %	11.50               5.56               4.32               1.24               7.18           62.47A               5.94           51.65A	7.55             4.56             4.28             0.28             3.27         43.33B             2.99          39.66B	7.34               3.22               3.09               0.13               4.25           57.96A               4.12           56.16A
AB indicates significant difference (P < 0.05). AA indicates no difference. Statistical differences for other response variables are not presented in this table. Source: ADM Alliance Nutrition - Swine Test 01601B

The addition of phytase to the diets of growing and finishing swine did not alter growth performance. ADM Alliance Nutrition Research has shown the addition of 300 units of phytase per kg of diet did not negatively impact growth performance when compared to diets containing 0.1% more phosphorus (Table 3). Oklahoma State University observed similar results when 666.6 units of phytase per kg of diet was used to assess growth performance of pigs from 144 to 238 lb. No difference was observed in growth performance when pigs were fed diets with 0.33 or 0.5% total phosphorus (0 or 0.17% added phosphorus; Table 4).
 

Table 3  Effect of Replacing 0.1% Available Phosphorus with Phytase on Growth Performance of Growing and Finishing Swine
	Control	Phytase
Average Daily Feed Intake, lb Grower 1 Grower 2 Finisher 1 Finisher 2 Combined Average Daily Gain, lb      Grower 1 Grower 2 Finisher 1 Finisher 2 Combined Feed:Gain Ratio      Grower 1 Grower 2 Finisher 1 Finisher 2 Combined	2.89 4.32 5.54 7.19 5.27 1.64 1.96 1.96 2.17 1.96 1.77 2.20 2.83 3.31 2.68	2.95 4.34 5.65 6.78 5.18 1.71 1.96 2.12 1.99 1.96 1.73 2.22 2.66 3.41 2.63
Source: ADM Alliance Nutrition - Swine Test 97205

 

Table 4  Effect of Phytase Supplementation on Performance of Finishing Pigsa
	Control	Low Phos	Phytase + Low Phos
Avg. Daily Gain, lb Avg. Daily Feed Intake, lb Feed:Gain Ratio	2.16b     8.00     3.69d	1.94c           7.93           4.11c	2.14b              8.31              3.88de
a   Data are means of four pens of four pigs each.  Average initial and final weights were 144 and 238 lb, respectively. b,c  Means within a row lacking a common superscript differ (P<.10). d,e  Means within a row lacking a common superscript differ (P<.05). Source: Oklahoma State University, 1996

Phytase Stability and Shelf Life
Product stability or shelf life of phytase is a concern for manufacture of phytase-containing feeds and subsequent product inventory. Phytase activity over time has been extensively tested and found that it can be negatively affected by:

• Heat

• Moisture

• Pressure

• Trace elements

• Time

Research has shown phytase enzyme activity can decrease rapidly over time when subjected to heat. The percentage of enzyme activity at three months decreased markedly when temperature increased from 50º F to 86º F. Percentages of enzyme remaining after three months were reported as 97, 88, and 60% of original when stored at 50, 68, or 86º F, respectively. Increasing humidity with increasing temperature further decreased enzyme activity.

Stability of phytase in base mixes or premixes is another key area of concern given the adverse affects of trace minerals and hygroscopic substances, such as choline chloride and sodium chloride. BASF (the manufacturer of Natuphos®*) tested several base mixes using storage condition of 73º F and 50% relative humidity. They reported that Natuphos retained 75% of its activity after three months under these conditions. After two months of storage at 86º F, only 65% of original activity was maintained. Based on these data, it is obvious that storage conditions can play an important role in maintaining the shelf life of phytase.

Pelleting can also be stressful to enzymes such as phytase. Natuphos phytase does not withstand temperatures required for pelleting and thus requires post-pelleting liquid application when used in pelleted diets. Ronozyme®*P (CT) phytase is reported to survive the pelleting process better than Natuphos phytase. Research from DSM Nutritional Products, Inc. (Ronozyme supplier) indicates phytase retention rate was approximately 40% higher for Ronozyme than Natuphos at 185º F. Therefore, it is suggested to use Ronozyme in pelleted diets when post-pelleting liquid application is not available.

Summary
Phytase is an enzyme proven to be effective in releasing phosphorus from phytic acid. It effectively increases phosphorus availability from typical cereal grains and soybean meal. However, use of phytase is not without limitations:

• Limited shelf life, especially during summer months due to effects of heat and humidity.

• Limited capacity to withstand temperatures needed for manufacture of pelleted feed.

The use of phytase is a proven technology that reduces environmental phosphorus sourced from swine manure, while maintaining swine performance. The decision to include phytase in swine diets will depend largely on individual economic and environmental situations. *Not trademarks of ADM.

For additional information E-mail: AN_SwineHelp@adm.com
Or call ADM Alliance Nutrition Inc, Customer Service 866-666-7626