Research at Iowa State University shows supplementing conjugated linoleic acid (CLA) in swine diets improves feed efficiency, decreases fat deposition and improves the firmness of the hog’s belly.

For the project, eight replications of five littermate barrows were penned individually, beginning at 58 lb. Diets included 0, 0.12, 0.25, 0.5 and 1.0% CLA. The diets contained 18.7% crude protein and 1.0% lysine and then were reformulated every three weeks (six phases). In the final finishing stage, diets contained 12.3% crude protein and 0.55% lysine. The CLA was substituted for corn. Pigs were weighed and feed disappearance determined every 14 days.

Real-time ultrasound was used to determine backfat and loin eye area at 114, 150, 200 and 250 lb. Pigs were slaughtered at 255 lb. at the Iowa State Meat Laboratory for total loin dissection and primal to wholesale-ready cut measurements.


Average daily gain (ADG) increased as the concentration of CLA in the diet increased. ADG was 2.24 lb. for pigs fed 1.0% CLA, compared to 2.07 lb. for pigs fed the control diet. Pigs fed 0.5% CLA had an ADG of 2.14 lb.

Average daily feed intake (ADFI) was 5.90 lb. for the control diet and 5.79 lb. for both 1.0% and 0.5% CLA-diet-fed pigs.

First-rib backfat tended to decrease linearly, as demonstrated by a –3.91% difference at .12% CLA and a –15.65% difference at 1.0% CLA. Last rib and last lumbar fat depth was not different between treatments and controls.

Researchers found that fat depth decreased at 200 lb. of liveweight for pigs on the 0.12% CLA treatment. This difference was maintained at 250 lb. for the 0.12 and 0.25% CLA treatments.

The ultrasound results showed an increase in loin eye area (LEA) for 1.0% CLA treatments between 200 lb. and 250 lb.

Within the individual wholesale-ready cuts, researchers found no difference in finished ham, loin or picnic weights, but did find heavier butt weight for the 1.0% CLA treatment pigs.

The most obvious difference was the hardness (firmness) of the belly. The researchers measured the belly by suspending the longitudinal midpoint of the belly across a stainless steel rod and measuring the distance in centimeters between the ham and shoulder end, with either the lean side up or down.

Pigs fed 0.5 and 1.0% CLA had firmer bellies, which provide the potential for improvement in sliceability and an increase in yield of bacon.

The researchers believe the firmer bellies are a result of a higher ratio of saturated:unsaturated fatty acids in the belly fat.

Further study is necessary to define the most appropriate dose required to optimize pig performance, economy of gain and body composition.

Researchers: F.C. Parrish, R.L Thiel-Cooper, J.C. Sparks, Bryon Wiegand and Richard Ewan, Iowa State University.

Contact Ewan at (515) 294-5132 or email: