Odor and Nutrient Management Newsletter

Fall 2001

Dietary phytase study shows positive results

by Larry McMullen, Jones County Extension; and Sherry Hoyer, Iowa Pork Industry Center

A yearlong demonstration project on the effect of dietary phytase on phosphorus levels in manure has yielded positive results. In the study, funded by the Iowa Pork Industry Center, phytase was fed to finishing pigs in treatment and control groups. In general, positive results were seen in several areas: phosphorus content in liquid manure was reduced by more than 23 percent over that of control diets, phytase inclusion did not reduce pig performance as measured by average daily gain and feed efficiency ratios, and phytase inclusion did not increase the cost of the diet.

dietary phytase study photoPhytase is an enzyme that breaks down the indigestible phytic acid (phytate) in grains and oil seeds and releases more digestible phosphorus that pigs can use. By reducing the unused portion of phosphorus in feed, less phosphorus is eliminated in manure, which is important for producers because of water quality concerns due to phosphorus in manure moving off-site and into surface waters. It is possible that future manure management plans in Iowa will require producers to address phosphorus application rates. If phosphorus-based rather than the current nitrogen-based plans are required, it could take approximately twice the land base for manure application.

When choosing to use phytase, producers must be aware of the correct or appropriate levels of phosphorus at specific levels of the production stage, which means the amount of inorganic phosphorus sources (for example, dical) can be reduced in the diet.

Phytase activity is measured in “phytase units” such as FTU/lb or FTU/kg. Currently, if a corn–soy diet is being fed to finishing hogs, the inclusion of phytase in the diet would be approximately 115 to 150 FTU/lb of diet fed. Adding phytase to swine diets is easy because premixes containing phytase are readily available from most commercial feed companies. However, you must remember to calculate and review feed rations to make sure you are not overfeeding inorganic phosphorus sources in the diets. As a rule of thumb when feeding phytase in swine diets, the percentage of reduction of the inorganic phosphorus will be the amount of phosphorus reduced in the swine manure.

Reducing phosphorus in swine manure through the use of dietary phytase has several environmental advantages. In addition to reducing the crop acres needed for manure application, this practice can help to limit the buildup of soil phosphorus levels. Also, it helps reduce potential water pollution due to nutrient runoff and leaching. And, if a phosphorus-based manure management plan is approved by the Iowa legislature, using phytase will enable producers to comply with state regulations.

Although this study shows promising results in terms of reducing phosphorus levels in manure by including phytase in the diets, there are factors that affect the level of phosphorus reductions in different operations and even in different buildings within the same operation. One of these factors is related to feed ingredient variation and amounts, such as levels of phosphorus, calcium, and protein in a specific diet. Also, using an incorrect ration formulation for phosphorus and calcium with phytase might affect the reduction. And, the amount of manure dilution with wastewater can easily distort or change a projected or expected reduction level.

Regardless of whether you are using phytase in your swine diets, for the correct manure application rate for your acres, have the manure analyzed for nitrogen, phosphorus, and potassium. Do not guess on the analysis because nutrient levels can vary. Applying appropriate amounts and keeping accurate records are imperative, and if there is a switch to phosphorus-based levels, your record keeping skills will be just as important.

For more information on this project, call (319) 462-2791 or e-mail lkmcmull@iastate.edu.

Project specifics
  • Four trials of grow/finish pigs, conducted from November 1999 to December 2000.
  • Location was room 1 of the Kirkwood Community College finisher unit in Cedar Rapids.
  • Each trial had a control diet group and a phytase diet group. Approximately 50 head were allocated to each diet group per trial.
  • Each diet group had a separate manure pit for accurate measuring. Initial water level in each pit was equalized to 30 gallons per pig to give a 5–6-inch beginning level.
  • Liquid and solid manure samples were collected every 2 weeks for each diet group.
Project implications
  • Phytase addition did not impair pig performance.
  • Diet costs were not increased.
  • Liquid and solid phosphorus levels were reduced significantly with phytase addition: phosphorus in liquids (–23.16 percent), phosphorus in solids (–17.60 percent), P2O5  in liquids (–22.11 percent), P2O5  in solids (–17.79 percent).
  • With a 22 percent reduction in liquid manure P2O5 level, a manure management plan based on phosphorus that required 100 acres would now need only 78 acres.

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Iowa Manure Matters: Odor and Nutrient Management is published by Iowa State University Extension, with funding support from the USDA Natural Resource Conservation Service through Cooperative Agreement No. 74-6114-8-22. To subscribe or change the address of a current subscription, write to Angela Rieck-Hinz, 2104 Agronomy Hall, Iowa State University, Ames, Iowa, 50011-1010 or call 515-294-9590, fax 515-294-9985 or email: amrieck@iastate.edu. Please indicate you are inquiring about the Odor and Nutrient Management Newsletter. The newsletter's coordinators are Angela Rieck-Hinz, extension program specialist, Department of Agronomy, Wendy Powers, environmental extension specialist, Department of Animal Science, and Robert Burns, Department of Agricultural and Biosystems Engineering; the editor is Jean McGuire, the subscription manager is Rachel Klein, the production designer is Beth Kroeschell, and the web page designer is Liisa Jarvinen.

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