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Better ways found to predict energy value in feed ingredients

alffoto/iStock/Thinkstock soybean harvest
Gross energy can be predicted accurately for some ingredients if traditional analyses are complemented by additional analyses.

To formulate cost-effective livestock diets based on energy, it's vital to know the energy content of feed ingredients as accurately as possible. Researchers at the University of Illinois are working on more accurate ways to predict the energy value of ingredients.

Hans Stein, professor in the University of Illinois department of animal sciences, said the feed components presented in composition tables usually don't add up to 100%, which indicates that not all energy-contributing components are accounted for.

"Analyzing all chemical components in feed ingredients is challenging," Stein said. "However, we believe that being able to analyze all energy-contributing components in a feed ingredient is likely to yield more accurate estimates for the energy value in that ingredient."

A team of researchers led by Stein set out to test the hypothesis that if all chemical components in the ingredient were accounted for, gross energy — calculated by adding values from all energy-containing components in feed ingredients — would equal analyzed gross energy.

They studied 10 ingredients that varied in fiber concentration and composition: corn, wheat, soybean meal, canola meal, dried distillers grains with solubles (DDGS), corn germ meal, copra expellers, sugar beet pulp, synthetic cellulose and pectin.

In addition to the traditional analyses for components such as crude protein, starch, fiber and fat, Stein's team also analyzed the 10 ingredients for tannins, sinapine, glucosinolates, glycerol, fructo-oligosaccharides and a number of soluble carbohydrates.

Their hypothesis didn't hold true for all ingredients, according to the announcement. The calculated gross energy was 8% greater than the analyzed value for corn, 12% greater for pectin and 12% less for DDGS and sugar beet pulp. Stein said this is likely due to inaccuracies in measurement as well as insufficient knowledge about the energy value of components that are analyzed less frequently.

"Some energy-contributing components may be analyzed as a different component of the feed ingredient. It's also possible that the gross energy values we use for lignin, tannins, sinapine and other components in the ingredient are inaccurate," he said.

However, the calculated gross energy values for wheat, soybean meal, canola meal, corn germ meal, copra expellers and synthetic cellulose were within 4% of analyzed gross energy for these ingredients, indicating that the analyzed components appear to be accurate.

"You don't get the complete picture on energy content without analyzing all energy-contributing components, in particular low-molecular weight carbohydrates," Stein said. "Our data indicate that, at least for some ingredients, it's possible to predict gross energy accurately if traditional analyses are complemented by additional analyses, primarily of soluble carbohydrates and lignin."

In another phase of the experiment, the team simulated apparent ileal digestibility and apparent total tract digestibility of the ingredients using an in vitro procedure. They found that the traditionally analyzed fiber components — acid detergent fiber (ADF) and neutral detergent fiber (NDF) — may not be the best predictors of the fiber value in ingredients, the University of Illinois said.

"Instead of ADF and NDF, we recommend analyzing insoluble fiber and total dietary fiber to estimate digestibility, because these values are better correlated with digestibility of dry matter and organic matter," Stein said.

The paper was published in the Journal of Animal Science. Co-authors were Diego Navarro of the University of Illinois and Erik Bruininx and Lineke de Jong of the Agrifirm Innovation Center in Apeldoorn, Netherlands, which provided funding for the study.

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