The effects of feeding different dietary levels of conjugated linoleic acid (CLA) and total oil (TO) were evaluated using 216 barrows fed from 36 to 115 kg body weight. A 3 x 2 factorial design was used with three levels of dietary CLA (0, 0.25, and 0.5%), two levels of dietary TO (2 and 5% made up with canola oil) and 12 pens of three barrows fed per diet. Pigs on all diets gained weight at the same rate from 0 to 4 wk (36 to 61 kg) and from 4 wk to slaughter (61 kg to 115 kg) (P > 0.05). Pigs fed 5% versus 2% TO had 6.6% lower feed intake from 0 to 4 wk (P = 0.02) and 5.9% lower feed intake from 4 wk to slaughter (P 0.003), while feeding CLA had no effect on feed intake (P = 0.70). A CLA by TO interaction for feed intake was not found for 0 to 4 wk but from 4 wk to slaughter a tendency for an interaction (P = 0.06) was found indicating 0.25% CLA may depress feed intake at 2% TO while stimulating intake at 5% TO. Increasing TO and CLA increased the lean content in commercial cuts by 1.6% (P = 0.06) and 2.7% (P = 0.008), respectively. A CLA by TO interaction (P = 0.012), however, indicated CLA was less effective at increasing lean when added to 5% TO diets than to 2% TO diets, with pigs fed the 0% CLA/2% TO diet yielding 5% less lean than pigs fed any of the other diets (P < 0.05). Interestingly, a main effect for TO was not found for subcutaneous fat (SCF), but adding CLA reduced SCF (6.6%; P = 0.002). Again, a CLA by TO interaction (P = 0.008) indicated adding CLA was less effective at reducing SCF in 5% TO than 2% TO diets, with pigs fed the 0% CLA/2% TO diet having 9.7% more SCF than pigs fed any of the other diets (P < 0.05). The difference in effectiveness of CLA at different TO levels might be due to dilution of CLA by canola oil fatty acids and/or canola oil having fat to lean repartitioning effects of its own. A comparison of fats and oils with differing drain lengths and degrees of saturation would, therefore, be of interest to further define their potential differential effects on growth and metabolism.
