Producers and feed companies add fat to swine diets to increase energy, but recent research from the University of Illinois suggests that measurements currently used for fat digestibility need to be updated.

"It's critical that we gain a better understanding of the energy value of fat," said Hans H. Stein, U of I professor in the Department of Animal Sciences. "If we don't know the true energy value of fat, we can't determine if it's economical to add to the diet."

In a recent experiment, Stein and his team of researchers studied how different types of diets affect endogenous losses of fat (fat excreted from pigs that did not originate from the diet). They measured endogenous losses of fat to determine the true digestibility of both intact and extracted corn oil. The intact corn oil was provided in the form of corn germ, and the extracted fat was provided as liquid corn oil.

Endogenous losses differed depending on the type of fat in the diet, he said. The intact fat was less digestible than extracted fat.

"We believe the main reason intact fat is less digestible than extracted fat is that it is easy for the enzymes to gain access to the fat in corn oil. In contrast, the corn germ is encased in the feed ingredient among the fiber complexes, which makes it difficult for enzymes to access and digest it," Stein said.

His team also discovered that measuring fat digestibility at the end of the ileum results in a more accurate value than measuring the total tract digestibility of fat.

"The microbes in the hindgut can synthesize fat," Stein explained. "This fat is not absorbed in the hindgut; it's just excreted in the feces. Because of this, it's easy to underestimate the amount of fat that was absorbed in the small intestine by the pig."