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Fungal Enzyme Could Help Livestock Retain Phosphate

By Jan Suszkiw
December 11, 1997

Chicken and hog feeds containing an enzyme called phytase can help improve water quality by reducing phosphate runoff from manure, Agricultural Research Service scientists report.

The scientists are developing a heat-resistant form of this enzyme that can be easily added to feed. Studies have shown that animals retain up to 60 percent of phosphate from feed when phytase is included in the feed. Without the enzyme, the animals naturally excrete the phosphate in manure, posing a waste disposal problem for farmers and a threat to water quality.

Although phytase has federal approval for commercial use, it is not widely used as a feed additive in the United States. The chief reason: The enzyme breaks down under the high temperatures used in the feed production process.

Geneticist Edward Mullaney and chemist Jaffor Ullah are designing a version of phytase that can take the heat--literally. They work at ARS' Commodity Utilization Research Unit in New Orleans. They have identified an isolate from the Aspergillus fungal family that makes a phytase that can withstand 160 degrees Fahrenheit for several minutes.

They are now using recombinant techniques to combine this heat stability with the high performance of a commercial phytase from another Aspergillus. The scientists are also seeking a commercial collaborator to help produce a superior enzyme for use by the animal feed industry.

In Maryland, the poultry industry has agreed to a state proposal to share the extra costs of adding commercial phytase to chicken feed. The proposal stems from concerns that runoff from manure-fertilized fields may be fueling outbreaks of the fish-killing microbe Pfiesteria piscicida in the waterways of Maryland's Eastern Shore.

Scientific contact: Edward Mullaney, Jaffor Ullah, ARS Commodity Utilization Research Unit, Southern Regional Research Center, New Orleans, La., phone (504) 286-4364, fax (504) 286-4367,,