Feeding Phytase to Growing Pigs: A Preliminary Cost/Benefit Assessment

Livestock Update, February 1999

Allen F. Harper, Extension Animal Scientist, Swine, Animal and Poultry Sciences, Virginia Tech Tidewater AREC

Supplementing swine diets with the enzyme phytase has been extensively researched over the past decade by European and U.S. swine nutritionists. A large database has been developed which characterizes the ability of the enzyme to make phytatebound phosphorus in feed concentrates (i.e. corn) and oil seed meals (i.e. soybean meal) nutritionally available to pigs. Briefly stated phytase supplementation to growingfinishing pig diets allows feed formulators to reduce inorganic phosphate inclusion rates by 50% or more while maintaining animal performance similar to that observed with traditional phosphate supplemented feeds. In conjunction with this practice is a 20 to 40 percent reduction in phosphorus excretion by the pig.

In most U.S. states including Virginia, manure nutrient management planning has been implemented as a means of strategic soil application of nutrients in manure. Historically these plans have based application rates on the nitrogen content of the manure and the expected nitrogen utilization rate of crops grown on application fields. However, due to rich phosphorus content of swine and other types of animal manure, application to meet crop nitrogen requirements can result in a net accumulation of phosphorus in the soil. Although phosphorus is much less prone to leaching out of soils than is nitrogen, there are concerns that overenrichment can lead to environmental problems. For example, erosion of soils containing high levels of phosphorus can lead to nutrient enrichment of surface waters and degradation of water quality.

There is an increasing emphasis on managing phosphorus along with nitrogen when utilizing swine and other animal manure. In the Netherlands livestock producers are faced with strict governmental quotas restricting the amount of phosphorus that can be applied to agricultural soils in the form of livestock manures. This emphasis is developing in the U.S. as well. Proposed revisions of the U.S. Clean Water Act (U.S.D.A.E.P.A., 1998) call for widespread implementation of manure nutrient management plans with emphasis on all important soil nutrients. And, recent legislated changes to Virginia's confined animal feeding regulations call for increased emphasis on avoiding buildup of soil phosphorus levels when applying liquid animal manure to cropland. Given these developments, the utilization of phytase in swine feeding has the potential to have a positive impact in the management of phosphorus levels in manure and the utilization of swine manure in acceptable nutrient management plans. Indeed the driving force behind increased use of phytase in swine and poultry feeding is to reduce phosphorus excretion and the risk of excess phosphorus application to agricultural soils. With the implementation of any swine feeding technology there are added costs and added benefits. The purpose of this brief paper is to give a simple assessment of added costs and added benefits associated with supplementing phytase in the diet of growing pigs under U.S. conditions.

Phytase premixes became commercially available in the U.S. in 1997 with the approval of a BASF Corporation product sold under the trade name Natuphos®. This product is available in several formulations including a liquid formulation containing 5000 phytase "units" per gram of product (Natuphos 5000L®) and dry products containing 1200 phytase units (Natuphos 1200®) or 600 phytase units (Natuphos 600®) per gram of product. The dry formulations are designed for direct addition to grind and mix diets that will be fed in meal or mash form. The concentrated liquid formulation may be used for spray addition to vitamin or vitaminmineral premixes. Phytase fortified vitamin and mineral premixes are subsequently added to grind and mix diets as a source of supplemental vitamins, minerals and phytase. More importantly, the liquid formulation is designed for postpellet sprayon application in larger feed mills in which feed is prepared by grinding, mixing and extrusion of the mash through a pellet mill die to produce pelleted feed. This process is critical because running feed through a pellet mill results in a substantial increase in feed temperature. Because phytase is a heat sensitive enzyme, it must be added to the diet as a spray on formulation after feed pellets have been produced and cooled. Fortunately, postpellet application technology has advanced in recent years. Reliable equipment is now available to apply liquid formulations of phytase in large feed mills producing pelleted feed.

In simplistic terms, the net cost (or savings) of a significant change in management is the sum of the added costs and added returns that result from the change. In the case of including phytase in growing pig diets, the net variable cost may be described as indicated in table 1. There will be a direct cost for the phytase premix. In addition minor increases in calcium supplementation of the diet will be required to correct for reductions in combined calcium and phosphorus supplements such as dicalcium or monocalcium phosphate. These added costs will be countered by added savings such as reduced phosphorus supplementation and other ingredient reductions resulting from phytase addition.

Table 1. Net Variable Cost (or Savings) With Phytase Supplementation.

Previous grower pig experiments have evaluated phytase mainly as a means to reduce phosphate supplementation. Reliable cost estimates may be applied to actual data from some of these experiments to assess the cost effectiveness of phytase. Table 2 shows diet formulation, cost estimates and pig performance for grower pigs in an actual experiment (Harper and coworkers, 1997). Using current reported ingredient prices and $12.00 per lb. as the cost of phytase (Natuphos 5000L®), the cost per ton of three diets evaluated may be reliably estimated. In this trial a standard diet (positive control) has a cost estimate of $142.61 per ton. A negative control diet with reduced dicalcium phosphate level and no added phytase costs slightly less at $141.61 per ton while a diet with enough Natuphos 5000L® to provide 500 units of phytase per kg of diet costs more at $144.00 per ton. Based on actual results, pigs fed the low phosphorus diet without added phytase grew slower and less efficiently than pigs fed the standard diet or the low phosphorus diet with added phytase. The experiment demonstrated that the poor performance in the low phosphorus diet was due to phosphorus deficiency and that phytase supplementation could overcome most of the observed reduction in pig performance. However, because the phytase supplemented diet was $1.39 higher in cost per ton and pig feed conversion was slightly poorer, there was a modest advantage in cost per lb. of gain with the standard diet formulation as compared to the phytase diet.

Table 2. Phytase Use -- Actual Data Set I^a

		Grower Diets (42 to 115 lbs.)b
	(Est. cost)	Standard	Neg. Control	Phytase
Ingredients, lbs/ton
Ground corn	$2.80/bu	1308.0	1315.4	1315.2
Soybean meal (48%)	200.00/ton	579.0	579.0	579.0
Fat	.16/lb	60.0	60.0	60.0
Dical. phosphate	280.00/ton	14.0	3.2	3.2
Ca carbonate	80.00/ton	17.8	21.2	21.2
Salt	.05/lb	12.0	12.0	12.0
Vitamin/trace min.	.70/lb	9.2	9.2	9.2
Natuphos 5000-Lc	12.00/lb	0.0	0.0	0.2
		2000 lbs.	2000 lbs.	2000 lbs.
Diet cost, $/ton		$142.61	$141.61	$144.00
Pig performance
Daily gain, lbs		1.70x	1.47y	1.66x
Feed/gain		2.07x	2.18y	2.10x
Feed cost/lb gain, $		.147	.154	.151

a	Adapted from Harper, Kornegay and Schell, 1997.
b	Standard diet formulated to contain .58% Ca, .50% P, 1.09% lysine and 1566 Kcal ME/lb. Negative control and phytase diets formulated to contain .53% Ca, .40% P, 1.09% lysine and 1572 Kcal. ME/lb.
c	Natuphos 5000-L supplemented at a level to provide 500 phytase units per kg of complete feed.
x,y	Means with different superscripts differ (P<.08).

A similar comparison on a second data set from the same study is presented in Table 3. In this trial Natuphos 600® was used as the source of phytase and monocalcium phosphate was the inorganic phosphorus supplement. Because Natuphos 600® is a less concentrated source of phytase enzyme, more must be added to provide the final feed with 500 phytase units per kg of diet. Cost results are similar to those in the first data set. The phytase containing diet cost $1.96 more per ton to formulate than the high phosphorus diet. Likewise, feed cost per lb. of pig gain was also slightly higher for the diet with phytase supplementation. In both examples these price relationships will change as the cost of phytase and cost of inorganic phosphate supplements change.

Table 3. Phytase Use - Actual Data Set II^a

		Grower Diets (64 to 154 lbs.)b
	(Est. cost)	Standard	Neg. Control	Phytase
Ingredients, lbs/ton
Ground corn	$2.80/bu	1546.8	1549.0	1547.3
Soybean meal (44%)	200.00/ton	419.2	419.2	419.2
Fat	.16/lb	0.0	0.0	0.0
Monocal. phosphate	340.00/ton	6.7	2.9	2.9
Ca carbonate	80.00/ton	14.3	15.9	15.9
Salt	.05/lb	6.0	6.0	6.0
Vitamin/trace min.	.70/lb	7.0	7.0	7.0
Natuphos 5000-Lc	12.00/lb	0.0	0.0	1.68
		2000 lbs.	2000 lbs.	2000 lbs.
Diet cost, $/ton		$121.98	$121.50	$123.94
Pig performance
Daily gain, lbs		2.02	1.88x	2.01
Feed/gain		2.74	2.87	2.82
Feed cost/lb gain, $		.167	.174	.174

a	Adapted from Harper, Kornegay and Schell, 1997.
b	Standard diet formulated to contain .41% Ca, .42% P, .80% lysine and 1506 Kcal ME/lb. Negative control and phytase diet calculated to contain .41% Ca, .38% P, .80% lysine and 1508 Kcal. ME/lb.
c	Natuphos 600 supplemented at a level to provide 500 phytase units per kg of complete diet.
x	Negative control daily gain poorer than standard and phytase means (P<.01).

Current studies are focusing on the effectiveness of phytase supplementation to make additional calcium, protein, amino acids and energy available from the diet. Although the predominant effect of phytase is in making more phosphorus available to the pig, it does appear that some additional calcium and protein is made available and space is made available in the diet for higher energy, lower cost ingredients such as corn. The BASF Corporation recently published some example diets that were formulated by assigning phosphorus, calcium and protein nutrient values to phytase (McKnight, 1998). Cost comparisons of two of these example diets, one with phytase and one without, are given in Table 4. If phytase can be relied upon to make more protein available along with phosphorus and calcium, the diet may be formulated to contain less inorganic phosphate (dicalcium phosphate), less protein supplement (soybean meal), and less added fat. In this case, phytase supplemented diets may actually cost less per ton than comparable diets formulated to provided the same available phosphorus, calcium, protein and energy levels. Studies are currently being planned to test if such diets have application under commercial conditions.

Table 4. Phytase Use - Assuming Protein and Energy Adjustments^a

		Grower Dietsb
	(Est. cost)	Standard	+ Phytase
Ingredients, lbs/ton
Ground corn	$3.09/bu	1495.7	1546.3
Soybean meal (44%)	239.40/ton	408.0	386.0
Fat	.125/lb	33.0	18.0
Dical. phosphate	280.00/ton	29.4	14.2
Ca carbonate	25.80/ton	19.5	20.5
Salt	.023/lb	8.6	8.6
Vitamin/trace min.	1.07/lb	4.5	4.5
LysineÐHCI	1.24/lb	1.3	1.7
Natuphos 5000-Lc	12.00/lb	0.0	0.2
		2000 lbs.	2000 lbs.
Diet cost, $/ton		$146.36	$145.10

a	Suggested diets published by McKnight, 1998.
b	Standard diet formulated to contain .75% Ca, .60% P, 85% lysine, 16% protein and 1474 Kcal ME/lb. Phytase diet formulated to contain .63% Ca, .48% P, 85% lysine, 15.7% protein and 1474 Kcal. ME/lb.
c	Natuphos 5000-L supplemented at a level to provide 500 phytase units per kg of complete feed.

An additional return or cost savings associated with utilization of phytase in swine feeding may be the value of reduced phosphorus content of swine manure. In the experiments cited in Tables 2 and 3, phosphorus excretion was reduced by over 21 percent. In other reported experiments, phosphorus excretion has been reduced even more. However, estimating the value of reduced phosphorus excretion is difficult and would vary significantly under different farm conditions. For example, farms with a large land base for manure application and utilization of phosphorus in crop production would realize only modest returns from reduced phosphorus content of manure. But, farms with limited application acreage may realize substantial benefits from reduced phosphorus content of manure. This added benefit would be especially important in situations where manure management plans dictate a reduction in the amount of phosphorus that may be applied to a fixed acreage of cropland.

Using a modeling approach, Bosch and coworkers (1998) have estimated the economic benefits for a 27.75 % reduction in phosphorus content of swine manure when dietary phytase supplementation is used.

The model farms were swine finishing farms each with six finisher houses with a combined capacity of 4958 hogs (45 to 240 lbs.). Anaerobic lagoons were the assumed manure storage and treatment systems. There were two scenarios, one with a low land base (44 acres) producing bermudagrass hay and another with a higher land base (106 acres) producing corn grain.

Under all circumstances manure disposal resulted in a net cost to the operation. When the nutrient management plan was changed from a nitrogen basis to a phosphorus basis, manure application acreage needs increased from 44 to 98 acres for the bermudagrass hay system and from 106 acres to 191 acres in the corn grain system. Total manure disposal costs increased from $26,906 to $54,705 for the hay system and from $34,461 to $61,423 for the corn grain system. When phosphorus excretion is reduced with phytase, the acreage increase needed for the phosphorus based manure plan is decreased. Furthermore total manure disposal costs are also decreased. In the final analysis that included diet cost changes and phosphorus based manure management, Bosch and coworkers estimated that phytase supplementation resulted in $0.49 per hog in additional net returns when owned cropland for manure application included only 44 acres of bermudagrass hay. The returns were $0.02 per hog when cropland for manure application included only 106 acres of corn.

Summary
In summary, phytase supplementation of low phosphorus growing pig diets has been demonstrated to reduce phosphorus excretion in manure by more than 20 percent while maintaining pig performance similar to levels observed with standard phosphate supplementation. Premixes for supplementing phytase to U.S. swine and poultry feeds became available in 1997 with the approval of BASF Corporation products Natuphos 5000L® (liquid formulation) and Natuphos 600® and 1200 (dry formulations). In situations where only meal type feeds are produced and fed, phytase may be supplemented by simply mixing the proper level of dry phytase premix in the feed with standard mixing equipment. However, in large central feed mills producing pelleted feeds, phytase must be applied in a liquid sprayon application after pellets have been milled and cooled. This is necessary because heat caused by the pelleting process can decrease phytase enzyme activity. Fortunately, technology and equipment is available to allow efficient application of liquid enzyme preparations to pellets in high production rate feed mills.

Phytase supplementation results in added costs and added benefits (savings) in swine feeding. The most direct cost when supplementing phytase is for the phytase product. The most direct savings is in reduced quantity of inorganic phosphates added to the diet. The actual dietary costs associated with supplementing phytase will vary with the cost of the phytase product and with the cost of inorganic phosphorus supplements. Based on actual data sets with growing pigs and using current ingredient cost estimates, phytase supplementation results in a net cost increase of $1.00 to $2.00 per ton of finished feed. Associated with this small increase is a slight increase in feed cost per pound of pig gain. Data is coming available that may indicate that phytase supplementation will allow other cost efficiencies in the feed formulation including some reduction in protein supplement (soybean meal) level and greater energy density of the diet. As this technology develops, phytase supplementation could become more cost effective and may actually result in lower finished feed cost than traditional phosphate supplemented diets.

The most substantial benefit associated with phytase use is a major reduction in phosphorus excretion by the pig. Although this benefit is difficult to estimate in exact terms, it definitely has economic and environmental value. In situations in which swine manure application rates are limited by manure phosphorus content, the net returns to phytase can approach $.049 per growingfinishing pig produced. Such an increase in returns would result primarily from lower land requirements for manure applications, less nitrogen and potash fertilizer requirements for crop production and lower application costs.

References
Bosch, D. J., M. Zhu, and E. T. Kornegay. 1998. Net returns from microbial phytase when crop applications of swine manure are limited by phosphorus. J. Prod. Agric. 11: 205213.

Harper, A. F., E. T. Kornegay, and T. C. Schell. 1997. Phytase supplementation of lowphosphorus growingfinishing pig diets improves performance, phosphorus digestibility, and bone mineralization and reduces phosphorus excretion. J. Animal Sci. 75:31743186.

McKnight, W. F. 1998. Swine ration formulation wth Natuphos phytase. BASF Technical Symposium Proceedings pp. 91109, Nov. 16, Durham, N.C. BASF Corporation 3000 Continental Drive, Mt. Olive, NJ 07828-1234.

United States Department of Agriculture and Environmental Protection Agncy. 1998. Draft unified national strategy for animal feeding operations. U.S.D.A., Mail Stop 2220, 901 D St. SW, Rm. 802, Aerospace Bldg., Washington, DC 20250-2220.

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