Scientists Examine Energy Value, Digestibility of Livestock Feed

29 July 2015, at 12:00am

US - 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, explained Hans H Stein, a University of Illinois professor of animal sciences.

"Grain co-products contain more fiber and non-starch polysaccharides (NSP) 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,” Mr Stein said.

“The addition of carbohydrate degrading enzymes can help improve fibre and NSP digestibility, but first we need to know which carbohydrates are present so that we can select enzymes accordingly."

Mr 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 (DDGS), 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 per cent of corn, 69 per cent of sorghum, and 61.8 per cent of wheat. Co-products ranged from 2.5 per cent starch in sorghum DDGS to 22.6 per cent in corn bran.

The NSP content of co-products ranged from 24.7 in sorghum DDGS to 41.8 per cent in corn bran. Arabinoxylans made up the largest per centage 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," Mr Stein noted.

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 per cent in corn bran to 57.3 per cent 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," said Mr Stein. "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 co-products from these grains," was published in a recent issue of the Journal of Animal Science.

Further Reading

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