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Alternative feed ingredients such as extruded expelled soybean meal (EESM) and dried distillers grains with soluble (DDGS) have been successfully included in swine diets. However, both feedstuffs increase the amount of unsaturated fats in the diet and, therefore, may influence carcass fat quality. Taking into account that the iodine value (IV) of a fat source is an estimate of the proportion of unsaturated fatty acids in that source of fat, the carcass fat IV is an indirect indicator of the percentage of unsaturated fatty acids, softness of fat, or rancidity. For all these reasons, the objective of this study was to evaluate the effects of dietary IV product (IVP) on finishing pig growth performance and carcass fatty acid composition. A total of 120 barrows (initial BW = 47.9 ± 3.6 kg) were used in an 83-d study. Pigs were blocked by BW and randomly allotted to 1 of 6 treatments with 2 pigs per pen and 10 pens per treatment. Dietary treatments were fed in 3 phases and formulated to 3 IVP concentrations (low, medium, and high) in each phase. Treatments were 1) corn-soybean meal control diet with no added fat (low IVP), 2) corn-EESM diet with no added fat (medium IVP), 3) corn-soybean meal diet with 15% DDGS and choice white grease (CWG) (medium IVP), 4) corn-soybean meal diet with low CWG (medium IVP), 5) corn-EESM diet with 15% DDGS (high IVP), and 6) corn-soybean meal diet with high CWG (high IVP). On d 83, pigs were slaughtered and backfat and jowl fat sample were collected and analyzed.
The calculated and analyzed dietary IVP values were highly correlated (r2 = 0.86, P < 0.01). Pigs fed the control diet, EESM, or high CWG had greater (P < 0.05) ADG than pigs fed EESM + DDGS. Pigs fed the control diet had greater (P < 0.05) ADFI than pigs fed all other diets. Pigs fed EESM + DDGS and high CWG had improved (P < 0.05) G:F compared with pigs fed the control diet or DDGS + CWG. Pigs fed diets with DDGS had greater (P < 0.05) backfat and jowl fat IV, C18:2n-6, and PUFA and less SFA than pigs fed all other treatments. Pigs fed EESM had greater (P < 0.05) backfat and jowl fat IV, C18:2n-6, and PUFA than pigs fed the control diet, low CWG, or high CWG. Pigs fed low CWG or high CWG had greater (P < 0.05) jowl fat IV than control pigs. Feeding ingredients high in unsaturated fatty acids, such as DDGS and EESM, had a greater impact on fat IV than CWG, even when diet IVP was similar.
Therefore, IVP was a poor predictor of carcass fat IV in pigs fed diets with different fat sources and amounts of unsaturated fats formulated with similar IVP. Dietary C18:2n-6 content was a better predictor of carcass fat IV than diet IVP.
JM Benz, MD Tokach, SS Dritz, JL Nelssen, JM DeRouchey, RC Sulabo and RD Goodband, 2011. Journal of Animal Science, 89:1419-1428. http://dx.doi.org/10.2527/jas.2010-3126