Dietary change shows promise in reducing swine waste odor

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URBANA, Ill. – Changes in swine feed components by using a natural enzyme, phytase, could reduce phosphorus concentration in swine wastes by as much as 50 percent, reducing the odor of the waste, according to a series of University of Illinois studies led by David Baker, professor emeritus in the Department of Animal Sciences.

Baker’s work was funded by the Illinois Council on Food and Agricultural Research as part of its five-year, $6 million swine odor and waste management project.

“Odor and other environmental pollutants originate in swine waste, and these are primarily derived from the feed,” Baker explained. “The nature of the odors and pollutants associated with swine waste, therefore, partly depend on the nature of the feed.”

One of the culprits is phosphorus, found in cereal grains and oil seeds including corn and soybeans.

It is organically bound as phytate but in this form it is poorly available to pigs because they lack phytase, the enzyme necessary to make the phosphorus available to the animal.

As a result, as much as 75 percent of the phosphorus ingested is excreted.

“We focused on adding various phytase compounds to swine diets to enhance utilization of phosphorus in corn and soybean meal to see if this lowered the amount of phosphorus excreted,” explained Baker.

The research involved feeding trials of phytase supplements at varying levels.

“In one study, we found that by formulating early/late (180-260 pounds) finishing pig diets using genetically-enhanced (low phytate) corn containing reduced amounts of indigestible phytate phosphorus and greater amounts of inorganic phosphorus can cut phosphorus excretion by up to 50 percent,” said Baker.

The studies also produced feeding recommendations for various stages of swine production and for varying types of microbial phytase.

“Adding phytase to swine diets will reduce the amount of phosphorus in the manure,” said Baker. “The amount of reduction will depend on diet type, phytase inclusion rate, degree of replacement of inorganic phosphorus, and the dietary concentration of phosphorus relative to animal requirements.

“As a general rule, the amount of phosphorus reduction in the diet will cause a similar phosphorus reduction in the manure. With the reduction of phosphorus in the manure, less land would be required for manure application.”

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