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.
Phytase
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.
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