LAUSR

Two experiments evaluated different fat sources and levels on growth performance, carcass characteristics, and economic impact in commercial finishing pigs. In experiment 1, 2,160 pigs (337 × 1,050, PIC; initially 37.3 ± 0.93 kg) were used. Pens of pigs were blocked by initial body weight and randomly assigned to one of four dietary treatments. Three of the four dietary treatments included: 0%, 1%, and 3% choice white grease. The final treatment contained no added fat until pigs were approximately 100 kg, and then a diet containing 3% fat was fed until marketing. Experimental diets were fed over four phases and were corn-soybean meal based with 40% distillers dried grains with solubles. Overall, increasing choice white grease decreased (linear, P = 0.006) average daily feed intake (ADFI) and increased (linear, P = 0.006) G:F. Pigs fed 3% fat only during the late-finishing phase (~100 to 129 kg) had similar G:F compared to pigs fed 3% for the entire study during the late-finishing phase, and intermediate G:F overall. Increasing fat tended to increase (linear, P = 0.068) hot carcass weight (HCW). Feed cost increased (linear, P ≤ 0.005) and income over feed cost decreased (linear, P ≤ 0.041) as choice white grease increased. In Experiment 2, 2,011 pigs (PIC 1,050 × DNA 600; initially 28.3 ± 0.53 kg) were used. Pens of pigs were blocked by location in the barn and randomly assigned to one of five dietary treatments arranged in a 2 × 2 + 1 factorial with main effects of fat source (choice white grease or corn oil) and level (1% or 3% of the diet) and a control diet with no added fat. Overall, increasing fat, regardless of source, increased (linear, P < 0.001) average daily gain (ADG), decreased (linear, P = 0.013) ADFI, and increased (linear, P < 0.001) G:F. Increasing fat increased (linear, P ≤ 0.016) HCW, carcass yield, and backfat depth. There was a fat source × level interaction (P < 0.001) in carcass fat iodine value (IV), where IV increased to a greater extent in pigs fed corn oil with only a small increase in IV in pigs fed diets with choice white grease. In conclusion, these experiments suggest that increasing fat from 0% to 3%, regardless of source, produced variable responses in ADG but consistently improved G:F. Increasing fat increased HCW, carcass yield, and backfat depth, but feeding diets containing corn oil increased carcass IV. With the ingredient prices used, the improvement in growth performance did not justify the extra diet cost from increasing fat from 0% to 3% in most situations.