Study: Carbohydrate composition in cereal co-products important to determine energy value

Study: Carbohydrate composition in cereal co-products important to determine energy value

Co-products derived from grains such as corn, wheat and sorghum are increasingly being used in livestock feed, and research at the University of Illinois is helping to determine the energy value of these grain co-products.

Knowing the specific composition of the carbohydrates in a feed ingredient is important for determining its energy value, explains Hans H. Stein, a U of I professor of animal sciences.

“Grain co-products contain more fiber and non-starch polysaccharides than the grains from which they are derived. These carbohydrates are digested less efficiently by pigs than starch, and can also decrease the digestibility of other nutrients,” Stein says. “The addition of carbohydrate degrading enzymes can help improve fiber and NSP digestibility, but first we need to know which carbohydrates are present so that we can select enzymes accordingly.”

Stein’s team conducted two experiments. In the first, they determined the carbohydrate composition of 12 feed ingredients: corn, corn distillers dried grains with solubles, corn gluten meal, corn gluten feed, corn germ meal and corn bran; sorghum and two sources of sorghum DDGS; and wheat, wheat middlings and wheat bran.

Starch made up 62% of corn, 69% of sorghum and 61.8% of wheat. Co-products ranged from 2.5% starch in sorghum DDGS to 22.6% in corn bran. The NSP content of co-products ranged from 24.7% in sorghum DDGS to 41.8% in corn bran. Arabinoxylans made up the largest percentage of NSP in all ingredients.

“These results indicate that exogenous enzymes that can hydrolyze arabinoxylans may be the most effective because the largest part of the NSP in corn and corn co-products, sorghum and sorghum DDGS, and wheat and wheat co-products is arabinoxylans,” Stein notes.

Testing digestibility

In the second experiment, the researchers tested the in vitro digestibility of NSP in the same ingredients. In vitro ileal digestibility was close to zero for most ingredients, indicating that pepsin and pancreatic enzymes do not degrade NSP. In vitro total tract digestibility of NSP ranged from 6.5% in corn bran to 57.3% in corn gluten meal. Both in vitro ileal and total tract digestibility correlated strongly with the concentration of NSP in the ingredient.

Even within the NSP fraction, composition matters. “If pigs are fed diets high in NSP, energy digestibility will be reduced,” Stein says. “But the composition of the NSP fraction affects fermentability. Ingredients with more soluble NSP will have a greater energy value than ingredients with less.”

The paper, “Carbohydrate composition and in vitro digestibility of dry matter and nonstarch polysaccharides in corn, sorghum, and wheat and coproducts from these grains,” was published in a recent issue of the Journal of Animal Science, and a subscription is required to read it online.

Co-authors include Neil W. Jaworski and Stein of the University of Illinois, and Helle Nygard Lærke and Knud Erik Bach Knudsen of Aarhus University, Denmark. 

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