Research Looks to Put More Tools in Your Phosphorus Toolbox

The most important anti-nutritional factor in swine nutrition, as it relates to nutrient management, is phytate. In traditional pig feed ingredients, 60-80% of the phosphorus (P) is present in the form of phytate, a compound that pigs are not able to use well. Bioavailability estimates of P in corn and soybean meal for pigs range from 10-30%. This low availability of phytate P poses two problems for producers - the need to add inorganic P supplements to diets, and the excretion of large amounts of P in the manure.

Phytate P must be hydrolyzed by an enzyme, phytase, into inorganic P before pigs can use it. Past research has proven that commercially available phytase (Natuphos, from BASF) can improve P digestibility. As a result, the total P levels in the diet are reduced, the efficiency of retention is improved and excretion of P into the environment is decreased (Table 1). In addition, feeds supplemented with phytase for grower-finisher pigs and for pregnant sows may need little or no supplementary feed phosphate. Currently, although the cost for adding phytase is somewhat offset by the savings realized by reducing P and calcium in the diet, it only appears to be cost effective in regions where penalties exist or costs are associated with disposal of manure with high levels of P.

Source: Simons et al. 1990.

Exploring the Impact of Phytase on P Excretion

Research has shown that the excretion of P can be reduced by 25-50% with the addition of 200-1000 units of phytase. Based on available information from Dr. E.T. Kornegay at the Virginia Polytechnic Institute and State University, a 109 kg pig consuming 318 kg of feed from 18 kg to market:

• would eat 1.43 kg of P, if fed NRC recommended levels (4.5 g P/kg diet)
  • would excrete about 0.71 kg of P
• would eat at least 1.11 kg of P, if phytase is added to the diet
  • would excrete about 0.56 kg of P or less
• would eat 1.75 kg of P, if fed higher than NRC levels (5.5 g P/kg diet)
  • would excrete at least 0.88 kg of P

Translate that to annual hog marketing figures and it means that, with approximately 5 million pigs in Ontario (average P excretion of 0.80 kg/pig), a 30% reduction in P excretion would represent about one million kg less P excreted annually.

New Phytase Enzyme from Yeast

Researchers continue to work at developing more tools for producers to use in the fight against phosphorus. Researchers at Cornell University recently uncovered a new phytase enzyme in a yeast system, Pichia pastoris. This new phytase, referred to as ECAP, is reported to be distinctively different from Natuphos in its biochemical properties. Three experiments were conducted with 140 weanling crossbred pigs (starting at 28 or 42 days of age for a period of 4-5 weeks) to assess ECAP in comparison to commercially available phytase. Overall, results showed that ECAP was as effective in improving phytate-P utilization by young pigs as Natuphos when included at levels of 700 or 1200 units/kg in corn-soybean meal diets.

This initial study relied primarily on plasma concentrations of inorganic P to make its conclusions but other researchers have suggested that other methods are more indicative of phytase efficacy. It is also of interest that, in the course of the investigation, ECAP was shown to have a single pH optimum of 2.5, compared to two pH optima of 2.5 and 5.5 for Natuphos. Undoubtedly more research needs to be completed before final conclusions can be reached on ECAP. The researchers plan to conduct further experiments to define appropriate inclusion levels for ECAP and the optimum conditions for its function in diets for different classes of pigs.

Unlocking the Mystery of True P Digestibility

Research at the University of Guelph is boldly delving into an area where no one has gone before. A team of researchers, led by Dr. Ming Fan, has recently developed a method to determine true P digestibility in feedstuffs for pigs. The idea is to use true digestible P values in formulating swine diets to ensure that the pigs are using P as efficiently as possible. They have proven, using soybean meal as the model feed ingredient for weanling pigs, that the current data available on P digestibility and availability underestimates the pig's use of P by at least 20% (Table 2). The ability to formulate diets on the basis of true digestible P will significantly reduce feed costs and P excretion into the environment. Further research is underway to determine true digestible P values in commonly used feed ingredients for different classes and breeds of pigs.

Source: Fan et al. 1999

References

Fan, M.Z., Archbold, T., Lackeyram, D., Rideout, T, Gao, Y, Squires, E.J., Hacker, R.R., de Lange, C.F.M., and Sauer, W.C. 1999. Formulation of Swine Diets on the Basis of True Digestible Phosphorus Supply. In: Symposium of the Hog Environmental Management Strategy (HEMS), December 10 and 11, 1999, Ottawa, Ontario.

Kornegay, E.T. 1996. Nutritional, Environmental, and Economic Considerations for Using Phytase in Pig and Poultry Diets. In: Nutrient Management of Food Animals to Enhance and Protect the Environment. Ed. E.T. Kornegay. Lewis Publishers.

Simons, P.C.M., Versteegh, H.A.J., Jongbloed, A.W., Kemme, P.A., Slump, P., Bos, K.D., Wolters, M.G.E., Beudeker, R.F., and Verschoor, G.J. 1990. Improvement of phosphorus availability by microbial phytase in broilers and pigs. Br. J. Nutr. 64:525-540.

Stahl, C.H., Roneker, K.R., Thornton, J.R., and Lei, X.R. 2000. A new phytase expressed in yeast effectively improves the bioavailability of phytate phosphorus to weanling pigs. J. Anim. Sci. 78:668-674.