Fat as an energy source has become commonplace in swine diets, but recent work by University of Illinois researchers suggests that the measures of fat digestibility need to be updated.

In a recent experiment, Illinois researchers studied how different types of diets affect endogenous losses of fat (fat excreted from pigs that did not originate from the diet) to get a better handle on 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.

The intact fat was less digestible than extracted fat, Stein notes. “We believe that 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,” he notes.

Researchers 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, but the 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,” he explains.

“We knew that the concentration of fat in the diet affects the value that is determined for apparent digestibility. However, by correcting these values for the endogenous losses, we can calculate the true digestibility of fat fed to pigs,” Stein says.

The research reinforces the need for more information on the digestibility of fat to ensure that swine diets are formulated economically.

“We now know that fat digestibility should be determined as ileal digestibility rather than total tract digestibility to avoid the influence of the microbes in the hindgut of pigs,” he continues. “We also know that for practical feed formulation, it is more accurate to use values for true ileal digestibility than for apparent ileal digestibility, because these values are not influenced by the level of fat in the diet.”

True ileal digestibility of fat in most feed ingredients used in swine diets is not known. Stein believes pork producers and swine nutritionists need a better understanding of how fat is utilized by the pig after absorption.

“It's critical that we gain a better understanding of the energy value of fat. If we don't know the true energy value, we can’t determine if it's economical to add to the diet,” he says.

The work of Stein and his associates was recently published in the Journal of Animal Science.