| The overall objective of this dissertation was to discern which components of the chemical composition of dietary fat affects the digestibility and energy content of dietary fat; the expression of genes involved in lipid metabolism; and the resulting carcass fat composition. Chapter 2, validated that dietary linoleic acid concentration was a more accurate predictor of carcass iodine value than iodine value product. Chapter 3, found that the addition of an unsaturated versus a saturated fat source did not alleviate the negative impacts associated with heat stress. Increased saturated fatty acid intake compared to increased intake of omega-6 fatty acids was found to decrease the mRNA abundance of fatty acid synthase (FASN) in adipose tissue in both Chapters 3 and 4. Decreased FASN mRNA content due to increased intake of saturated fatty acids would suggest that the de novo lipogenesis rate in adipose tissue is decreased. It was found in Chapter 5, that the DE content of dietary fat can be explained to a large degree by the chemical composition of dietary fat. However, the relationship between dietary fat DE content and its chemical composition was not the same between 13 and 50 kg of BW, respectively. In Chapter 6, it was found that the endogenous losses of fat accounted for 43% and 68% of fecal acid hydrolyzed ether extract at 13 and 50 kg of BW, respectively. Consequently, implying that the DE content of dietary fat is underestimated by 0.42 and 0.60 Mcal/kg, at 13 and 50 kg of BW, respectively, when measured on an apparent basis. This dissertation indicates that more work is needed to validate the DE, ME and NE estimates of dietary fat; to determine if dietary fat DE content needs to be adjusted for endogenous losses; to build a model that uses the chemical composition of dietary fat source and the energy intake of the pig, to explain observed lipid deposition rates and carcass fatty acid composition. |
