Young Scholar Presentation: The Impacts of Dietary Fat Source on Lipid Digestion, Absorption, Deposition, and Metabolism in Grow-Finish Pigs

Dietary fat sources are diverse in their chemical composition (fatty acid chain length, degree of unsaturation, free fatty acid content, non-elutable material, and peroxidation status). Fat is added to swine diets to provide dietary energy when the cost per kg of feed or gain is advantageous. However, little information is available for producers to adequately value different sources of dietary fat based on their chemical composition. Our objective has been to determine how chemical composition of dietary fat source impacts lipid digestion, absorption, deposition, and metabolism over a series of experiments ranging from individual fed pigs in intensive studies to pigs housed under commercial conditions. Fatty acid profile, and more specifically dietary linoleic acid, can be used to predict carcass iodine value (iodine value = 49.94 + [7.00 × dietary linoleic acid %]; P < 0.001), and is a more accurate predictor of carcass iodine value than iodine value product (R² = 0.95 vs 0.85; respectively). Furthermore, the fatty acid profile of the source can alter the mRNA abundance of genes involved in de novo lipogenesis, as the highly polyunsaturated dietary fat source corn oil had more mRNA abundance of FASN (fatty acid synthase), SCD (stearoyl Co-A desaturase), and SREBP-1 (sterol regulatory element-binding protein 1) than the more saturated fat source tallow (P ≤ 0.050). Degree of unsaturation and free fatty acid content of dietary fat sources can be used to determine the digestibility of dietary lipids; for example in nursery pigs, canola oil (90.7%) or fish oil (91.0%) had greater apparent total tract digestibility of acid hydrolyzed ether extract than the diets with the saturated fat sources palm oil (87.6%) or tallow (87.7%; P < 0.001), and in growing pigs the apparent total tract digestibility of acid hydrolyzed ether extract was greater in unsaturated fat based diets than saturated fat based diets, though the diet containing a high free fatty acid unsaturated corn oil source was the least digestible (P < 0.001). In conclusion, pork producers can determine energy value, predict carcass iodine value, and determine how sources of dietary fat will be utilized in the pig through the analysis of the chemical composition of dietary fats.