DDGS use affects phosphorus in hog, cattle manure

Feeding ethanol co-products to hogs should reduce the need for supplemental phosphorus in feed rations.

Jerry Shurson, Extension swine specialist with the University of Minnesota, says the P in co-products, such as distillers grains, is more available to the hog than P found in corn. This means less P ends up in manure.

He says research indicates adding 20 percent dry distillers grains (DDGS) to a nursery diet should result in the greatest reduction in phosphorus in manure, if the diet is formulated based on available P.

“With DDGS, about 90 percent of the phosphorus present is digestible by the pig,” Shurson says.

“Corn is about 28 percent total phosphorus, and only 14 percent of that is available to the pig.

“When we feed DDGS, we get a significant boost in phosphorus levels that are available.”

Adding a product, such as phytase, will make even more phosphorus available to the pig and reduce the amount of P in manure, he says.

“Adding 20 percent DDGS and phytase to the diet should decrease dietary P concentration as well as decrease daily P intake, fecal P concentration, and fecal and total P excretion, while increasing P digestibility and the percentage of phosphorus retained by the pig.”

Shurson says the DDGS plus phytase ration for nursery pigs should reduce manure P excretion by 36 percent, when compared to feeding a more traditional corn-soymeal diet without DDGS or phytase.

A similar diet in the grow/finish phase should significantly reduce phosphorus levels in the manure, he says.

While ethanol co-products can reduce the amount of phosphorus in hog manure, it’s just the opposite for feedlot cattle, notes Allen Trenkle, professor emeritus of animal science at Iowa State University.

“Grains are going to contain more phosphorus than forages, so in the feedlot, you are going to have more phosphorus in the manure,” he says. “If you are feeding distillers, there is no need for supplemental phosphorus.”

Trenkle says producers could replace some of the corn with DDGS or another ethanol co-product, which should result in a reduction of phosphorus in the manure.

“Feeding DDGS to growing and finishing cattle fed high-corn diets will result in increased phosphorus excretion that must be recognized and managed,” he says.

Trenkle says the situation is different with dairy cows.

“Lactating cows have a high phosphorus requirement, so you are going to need some supplemental P,” he says.

“You can take some of the corn out and put distillers in, and you won’t need any supplemental phosphorus.”

Ethanol co-products also could be used to supplement beef cows, Trenkle says.

“At times they eat a lot of low-quality forages, so DDGS can provide some of the phosphorus they are going to need,” he says.

Trenkle says a good manure-management plan should account for phosphorus levels.

“You really have to be aware of the phosphorus levels in the manure before you put together your manure-management plan,” he says.

“You may need to find more acres, but it’s important to get that manure out on that land that produces corn.”