Studies evaluate impact of nutrients in DDGS manure
As distillers grains becomes an ever more popular component of cattle diets in feedlots throughout North America, the need to explore the after-effects of that product also become more important. Canada’s Beef Cattle Research Council has funded several multi-year studies examining how the nutrients in distillers dried grains with soluble (DDGS) impact manure and found that the increased phosphorous and nitrogen levels will require feedlots to spread the manure over greater land base in order not to negatively impact soil quality.
Studies were carried out by researchers at the University of Guelph in Ontario, the University of Saskatchewan and Agriculture and Agri-Food Canada’s Lethbridge Research Center in Alberta. Diets containing varying amounts of DDGS derived from corn and wheat were fed to feeder steers or heifers weighing an average of 925 to 1050 pounds in three-week periods. The nutrient content of the manure, specifically nitrogen and phosphorous, was compared to a control group after each feed rotation period. Because there is no starch in distillers grains, researchers were unsurprised to find that the nitrogen and phosphorous contents in manure resulting from DDGS diets were higher. However they also found that as the amount of DDGS is increased in cattle diets, there is a point at which the animal does not absorb any more of the nutrient, thus even greater amounts are excreted. Additionally, distillers grains are less digestible than feed grain, so the amount of manure produced when feeding that product is greater than corn. This is especially true when feeding wheat-based DDGS compared to corn-based DDGS, according to Reynold Bergen, science director of the BCRC.
“When the manure is more concentrated, that means the feedlot has to have a larger land base to spread that manure on,” he said. “And if there’s more manure that’s more concentrated, they need an even bigger land base.”
The amount of phosphorous and nitrogen which can be applied to land varies by province in Canada, so some feedlots may face stricter regulations than others, Bergen said. He noted that the nitrogen to phosphorous ratio is less than optimal in manure, which can lead to a build-up of phosphorous in the soil if manure is applied to meet a crop’s nitrogen needs. “That can happen even with regular manure, so when you’re feeding distillers grains that will happen a lot faster,” he said. “That’s why the land base to spread becomes an issue.”
Depending on how far a feedlot has to haul the manure, feedlots could reach a point at which the price they are willing to pay for DDGS is impacted, Bergen said, adding that regional regulations and enforcement will play a role in determining the land base requirements. Ongoing studies are being conducted to further test nutrient content of DDGS-derived manure, comparing fresh versus composted manure and evaluating its performance on various soil types. “Ultimately what we’re trying to do is identify economically viable ways of dealing with some of these potential concerns,” he said.