Lipid peroxidation products can induce oxidative stress, compromise immunity, decrease intestinal function, and reduce growth performance. Therefore, it is important to characterize the oxidative status of lipids that are used in swine diets. However, the impact of the several quantifiable oxidative products that collectively describe peroxidation status on production performance has not been experimentally determined. We demonstrated that forced lipid peroxidation of soybean oil, using heat and oxygen perfusion, progressively increased markers of peroxidation with increasing time of exposure, resulting in decreased feed intake (by up to 7%) and growth rate (by up to 9%) when fed to nursery pigs. In addition, digestibility, absorptive capacity and morphology of the intestine were compromised with increasing peroxidation and these effects were related with disruption of the redox environment of the intestinal mucosa. The response of pigs to peroxidation products appears to be progressive and a minimum threshold for lipid peroxidation above which detrimental effects are detectable likely exists. We further demonstrated that peroxidation reduced serum vitamin E concentrations, indicating increased utilization of antioxidant components in pigs, even in pigs where growth performance was not significantly affected. Concurrently, feeding a synthetic antioxidant blend exerted a sparing effect as evidenced by increased serum concentrations of vitamin E. Although the impact of peroxidized lipids on growth performance may appear to be subtle, we clearly demonstrated in a large field study that increasing the level of peroxidation significantly increased mortality, number of pigs medicated, and number of pigs that were excessively light, resulting in reduced total pig weight produced at the end of the nursery. Although growth of pigs that remained in test pens was not affected, total pen gain was decidedly harmed because it takes into account pig mortality and removal for extensive medical treatment. Thus, quantification of peroxidation level of lipid sources for swine is critically important to design quality control programs for oil and fat sources and to increase profitability of pork production, especially for weaned pigs that are expected to be the most vulnerable to poor lipid quality.