Purdue University animal scientists are investigating the difference between the effects of conjugated linoleic acid (CLA) and the effects of lower feed intake on pig growth and carcass composition in lean genotype pigs.

Conjugated linoleic acid refers to a group of linoleic acid isomers that seem to have several biological effects. Scientists at the first annual CLA Forum reported pigs fed CLA had less backfat, less carcass fat, more carcass lean, improved feed conversion and firmer carcasses. Feeding CLA seemed to result in decreased feed intake while growth rate was unchanged, thus improving feed efficiency. The few studies that have been done regarding CLA for swine diets are shown in Table 3. These studies have seemed to show that CLA decreases backfat and increases fat firmness, but have been inconclusive in determining the effects of CLA on growth traits.

The Purdue researchers randomly assigned 30 lean-genotype gilts to one of three dietary treatments, starting at 165 lb. live weight. The diets consisted of conventional corn-soybean meal diets, supplemented with either 1.0% CLA-60 ad libitum (this was called the CLA diet), 1.0% sunflower oil ad libitum (SFO) or 1.0% sunflower oil restricted to the feed intake level of the CLA-fed group (RSFO).

Feed intake of the CLA pigs was determined weekly and fit to a quadratic equation as a function of live weight. This equation was used to determine the daily feed intake for the RSFO pigs. The design of the trial allowed the researchers to differentiate between the effects of CLA and the effects of lower feed intake on changes in growth and carcass composition.

Individual live weights and feed intake were obtained weekly for seven weeks. Ultrasonic, 10th- rib backfat and loin eye area images were collected weekly. These images were used to model lean growth and individual backfat layer growth. Pigs were slaughtered, tissue was collected and carcasses were evaluated at the Purdue Meat Laboratory. At slaughter, outer, middle and inner layer backfat, belly fat and loin were collected and snap frozen in liquid nitrogen until assayed for lipid and fatty acid composition. Standard carcass measurements such as backfat depths, loin eye area and subjective loin eye quality (color, firmness/wetness and marbling) were taken at 24 hours postmortem. Standardized loin slices were obtained for drip loss and for chemical analysis of fat and CLA. Bellies were removed from the carcasses and subjectively graded for firmness.

CLA-fed pigs demonstrated lower average daily gain (ADG). CLA-fed pigs also tended to have lower average daily feed intake (ADFI) and to be less feed efficient (FE), although the researchers say the results were not significant for these traits (Table 4). Restricted sunflower oil-fed pigs performed poorly in terms of ADG, ADFI and FE, which suggests the effects of CLA on the growth of pigs may be due to the effect of CLA on feed intake.

Neither the CLA or RSFO treatments had an effect on dressing percentage, ultimate (24-hour) pH, loin eye area, or subjective evaluations of loin color, firmness or marbling. Analysis of percent intramuscular fat remains in progress and will be reported in the future.

Both the CLA and RSFO treatments demonstrated a tendency, although not statistically significant, to improve drip loss and decrease kidney fat. The CLA-fed pigs tended to have less backfat, while the RSFO pigs tended to have more (Table 4). Although these differences in backfat were not significant, they demonstrate the effects of CLA on backfat thickness are not simply due to changes in feed intake.

CLA dramatically increased the firmness of bellies. RSFO treatment had a detrimental effect on belly firmness (Table 4). Approximately 50% of the SFO bellies for this genotype of pigs were questionable in terms of being firm enough to slice, while even the thinnest CLA-fed bellies were acceptably firm. This seems to further demonstrate the effects of CLA are not simply due to changes in feed intake. The researchers say they will try to better quantify differences in belly firmness in future trials in an effort to better define this effect. The question of how CLA improves belly firmness remains to be answered. The fatty acid profiles of the bellies from this trial are currently being determined, and the results will appear in a future report.

Analysis of the fatty acid composition of loins is reported in Table 5. CLA-fed pigs deposited more CLA in their loins, and deposited an amount of CLA which is similar to what they were fed (0.6%). The loins of CLA-fed pigs contained more saturated fatty acids and less unsaturated fatty acids, which resulted in a higher saturates-to-unsaturates ratio. CLA-fed pigs tended to have less mono- and poly-unsaturated fatty acids, but the results were not significantly different. Thus, the feeding of a poly-unsaturated fatty acid resulted in an increase in the amount of saturated fats. This result differs from the researchers' previous experiences in which the feeding of unsaturates has decreased the saturate-to-unsaturate ratio and resulted in a decrease in fat firmness. CLA may be affecting the regulation of genes that determine fatty acid composition. Future trials will determine the effects of CLA on such genes.

Future trials need to determine the effects of CLA on growth, composition and quality, and also seek to further understand the underlying biology that controls such traits. Because the effects of CLA will likely vary across genotypes, learning how CLA affects growth and gene expression will enable researchers to better determine at what level and for what duration CLA should be used by producers.

Researchers: J.M Eggert, M.A. Belury, and A.P. Schinckel, Departments of Animal Sciences and Foods and Nutrition, Purdue University. Contact Schinckel at (765) 494-4808.