Added fat in pig diets may affect nutrient digestibility

Supplementing pig diets with either saturated or unsaturated fat increases digestibility of calcium, phosphorus and sulfur in the diets.

Added fat increases the energy content of swine diets, but it may also affect the digestibility of nutrients. Dr. Hans H. Stein, professor of animal sciences at the University of Illinois, and a team of researchers have studied the effects of fat sources with different concentrations of saturated and unsaturated fatty acids on mineral digestibility.

"In pigs, addition of soybean oil to the diets has been shown not to reduce calcium digestibility. However, some studies in pigs and humans have observed the formation of indigestible calcium-fat complexes," Stein said. "These studies used fats that were more saturated than soybean oil."

Therefore, Stein and his team set out to determine the effect of the relative concentrations of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) on the apparent total tract digestibility (ATTD) of minerals in diets fed to pigs.

Five sources of supplemental fat were tested. Soybean oil and corn oil contained about 15% SFA, 26% MUFA and 57% PUFA. Palm oil and beef tallow contained about 46% SFA, 42% MUFA and 6% PUFA. The final fat source, choice white grease, contained 39% SFA, 43% MUFA and 13% PUFA.

The ATTD of calcium, phosphorus and sulfur was increased in pigs fed diets containing soybean oil, corn oil, palm oil or tallow compared with pigs fed diets containing no added fat or choice white grease, Stein said. Added fat did not affect the ATTD of potassium, manganese, sodium or zinc, although there was a tendency for magnesium digestibility to be greater in pigs fed diets containing soybean oil or corn oil, compared with pigs fed diets containing tallow or choice white grease.

"The implication of this experiment is that producers can include added fat, whether saturated or unsaturated, in diets for pigs without creating a reduction in digestibility of calcium or other minerals," Stein said. "However, in the case of choice white grease, there was some indication that it had been oxidized, and oxidation may reduce mineral digestibility."

Stein said this observation warrants further investigation.

The paper was published in a recent issue of the Journal of Animal Science. The full text can be found online at https://www.animalsciencepublications.org/publications/jas/articles/94/10/4231.

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