Extrusion is the norm in the pet and aquaculture feed industries, and while it remains unusual for swine feed in the U.S., the technology can improve energy and protein digestibility in pigs, according to research from the University of Illinois.

Hans H. Stein, professor in the University of Illinois department of animal sciences and the Division of Nutritional Sciences and co-author on a study reported in Animal Feed Science & Technology, said, "We're not doing this much in the U.S., partly because the extrusion equipment typically is not installed in feed mills producing pig feeds. If a feed company decided they wanted to extrude diets or extrude grain by itself, as we did in this case, it would add cost. So, the only way it would be economical would be if the pigs performed better with extruded grains.”

Stein and his research team compared pig diets containing either extruded or unprocessed corn, wheat and sorghum to determine ileal starch and amino acid digestibility as well as total tract digestibility of energy and fiber, the announcement said. One source of each grain was ground and then divided in two batches, with one batch left as is and the other extruded in a single-screw extruder with an exit temperature of 100°C.

For this study, grains were ground and extruded at Kansas State University, but extrusion equipment at the new Feed Technology Center at the University of Illinois will help facilitate future research.

“In extruded corn and wheat, we saw a nice improvement in amino acid digestibility -- corn in particular,” Stein said. “We observed increases for energy in extruded corn and sorghum, but not in wheat.”

Starch digestibility also increased in extruded grains compared with unprocessed grains.

“Starch is already well digested by pigs, but by extruding it, we increase its digestibility even more, and we have seen in quite a few other experiments [that] every time we increase starch digestibility, we increase energy digestibility,” Stein said. “There's a very, very close relationship between the two.”

The mechanical process of extrusion, which involves heat, pressure and steam, leads to gelatinization of starch, which explains the link between starch and energy digestibility.

“In the extruded grains, 90% of the starch was gelatinized,” Stein said. “Gelatinization opens the starch molecule, making it easier for enzymes to break down every bond within the starch. That leads to greater energy digestibility and absorption.”

Fiber digestibility did not change markedly in extruded grains versus unprocessed grains, but more of the fiber content became soluble with extrusion. “That means some of the insoluble fibers were solubilized, but because fiber digestibility didn’t increase overall, that didn't have as much of an impact as we had expected,” Stein said.

With pigs extracting more energy and protein from extruded grains, Stein said he sees a potential economic benefit that could justify the cost of adding extruding equipment to feed mills.

“If feed manufacturers can increase the energy as much as we did in our study, then there certainly is value in extruding grain for pig diets,” he said.

Authors on the article, “Digestibility of Amino Acids, Fiber & Energy by Growing Pigs & Concentrations of Digestible & Metabolizable Energy in Yellow Dent Corn, Hard Red Winter Wheat & Sorghum May Be Influenced by Extrusion,” include Diego A. Rodriguez, Su A. Lee, Cassandra K. Jones, John K. Htoo and Stein. The research was supported by Evonik Nutrition & Care.