It is common for vegetable oils to be supplemented to livestock diets to improve the energy density of the feed. Vegetable oils, however, have high concentrations of polyunsaturated fatty acids (PUFA). Due to this increased unsaturation, they are predisposed to lipid damage through lipid peroxidation. Lipid peroxidation is a dynamic free radical chain reaction that can be initiated by thermal processing in the presence of oxygen. This reaction progresses based on duration and intensity of thermal processing to produce a wide range of potentially oxidative and toxic compounds. Lipid peroxidation products of interest include peroxide value (PV) which measures hydroperoxides formed, and p-anisidine value (AnV) which is a measure of the molecular weight of aldehydes. Two key aldehydes are also formed including 2,4-decadienal (DDE) and 4-hydroxynonenal (HNE), are formed from the peroxidation of linoleic acid and are of interest because of their reactiveness with lipids, proteins, and DNA. Oils from ethanol, rendering or the restaurant industries may be an economical energy source compared to fresh oil, but at the expense of oil quality as they may be thermally peroxidized.

Consumption of these peroxidized oils may induce increased oxidative stress and antagonize livestock performance. Oxidative stress occurs in the event that oxidative compounds such as free radicals and reactive oxygen species (ROS) overwhelm the antioxidant defense system. Enzymatic antioxidants including superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) function in detoxifying (reducing) oxidative compounds to protect the body from oxidative stress. Oxidative compounds can bind to lipids, proteins, and DNA to stabilize resulting in tissue or cellular damage. Commonly, thiobarbituric acid reactive substances (TBARS) and F2-isoprostanes (ISP) are measured as indicators of lipid damage, protein carbonyls (PC) are measured as an indicator of protein damage, and 8-hydroxy-2'-deoxyguanosine (8-OH-2dG) is measured as an indicator of DNA damage. However, there is a poor understanding of the effects of feeding peroxidized oils on growth performance, digestibility, and oxidative status in livestock.

Therefore, the overall objectives of this thesis were to determine the impact of feeding peroxidized oils on growth and digestibility parameters, and whole body oxidative status in growing pigs and poultry. To accomplish these objectives, a series of experiments were conducted and are outlined in three chapters (Chapter 2, 3, and 4). In Chapter 2, an experiment was conducted feeding variable levels of peroxidized soybean oil (SO) on growth, digestibility, and intestinal integrity parameters in growing pigs. In Chapter 3 oxidative stress markers associated with lipid, protein, and DNA damage along with enzymatic antioxidants, were measured in pigs fed variable levels of dietary peroxidized soybean oil. The final chapter (Chapter 4) assessed the effects of feeding multiple fresh and peroxidized oil sources on growth performance and markers of oxidative stress in broilers.

The data herein indicate that thermally processing oils at 90oC for 72 h yielded the most harmful lipid peroxidation products as exhibited by reduced overall growth performance and feed efficiency in swine and poultry. Pigs fed thermally peroxidized SO (heated at 90oC for 72 h, 90oC SO) had reduced ADG, energy and lipid digestibility, and whole body N retention (Chapter 2). Further, these pigs also had increases in liver weight as a percentage of BW and generally had increased oxidative stress as measured by serum PC and GPx, urine ISP, and liver 8-OH-2dG (Chapter 3). To build on Chapters 2 and 3, Chapter 4 evaluated the effects of feeding fresh and peroxidized palm, soybean, flaxseed, and fish oils on performance and oxidative status in poultry. An interaction between oil source and peroxidation status was noted for ADFI, ADG, G:F, and plasma GPx in broilers where peroxidation status reduced each of these variables in birds fed palm, soybean, and flaxseed oil, apart from birds fed fish oil. In general, oil unsaturation increased plasma TBARS, PC and 8-OH-2dG; furthermore, broilers fed peroxidized oils had increased plasma 8-OH-2dG. An interaction was noted in liver TBARS where broilers fed peroxidized palm oil had increased liver TBARS compared to fresh palm oil, while the opposite was true in broilers fed soybean oil, and no change was noted in broilers fed flaxseed oil and fish oil. An interaction was also noted for liver PC where broilers fed palm, flaxseed, and fish oil had similar liver PC regardless of peroxidation status while broilers fed peroxidized soybean oil had increased liver PC compared to the fresh soybean oil diet. Generally speaking, the unsaturation content of the dietary oil increased liver 8-OH-2dG and CAT activity and peroxidation status increased liver SOD activity.

In summary, this thesis reported that formulating diets for pigs and poultry containing thermally processed oils (5-10% of total diet) were shown to have detrimental effects on performance particularly ADG. In pigs, thermally peroxidized SO also reduced digestibility of energy, ether extract, and nitrogen retention in comparison to pigs fed fresh SO. Additionally, growth performance was decreased in poultry fed peroxidized palm, soybean, and flaxseed oils. Oxidative stress was induced in swine and poultry fed peroxidized oils and different oil sources as measured in urine (pigs only), blood, and liver. Further, this data suggests that PV, DDE or AnV, PTAGS, and total tocopherols are important lipid peroxidation products that need to be measured as suggested by their consistent correlations with growth performance and oxidative status in swine and poultry. Additionally, these experiments and a review of literature indicate that markers of oxidative stress that should be measured include ISP and 8-OH-2dG in urine (pigs), and PC and GPx in blood (pigs and poultry). Overall, this thesis showed that oil quality should not be underestimated in livestock production. Feeding peroxidized oils can induce oxidative stress and antagonizes growth performance and digestibility in swine and poultry.