Date Full Report Received


Date Abstract Report Received



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BACKGROUND: A better understanding of methods to assess quality and feeding value of feed fats and oils is needed because of variability in composition and quality. Commonly used lipid quality measures such as moisture-insolubles-unsaponables, titer and free fatty acid content are used to insure that the lipid products meet trading specifications. However, these measures provide limited information regarding the feeding value of feed fats and oils and provide essentially no information regarding the degree of degradation, called peroxidation, of a given lipid source. Methods specific for evaluating lipid peroxidative stability can be divided into indicative and predictive tests. Indicative tests are used to measure the presence of peroxidation products in lipids and include: peroxide value (PV), thiobarbituric acid reactive substances (TBARS), p-anisidine value (AnV), conjugated dienes, hexanal value, 2, 4-decadienal (DDE), and 4-hydroxynonenal (HNE). Predictive tests measure the stability or susceptibility of lipids to peroxidation and include active oxygen method (AOM) and oxygen stability index (OSI). In predictive tests, the lipid is subjected to specific conditions that accelerate peroxidation and a peroxidation endpoint is defined to determine the degree of peroxidation damage. However, assessment of the degree of lipid peroxidation is complex because the process consists of three phases: (1) an initiation phase which involves the formation of free lipid radicals and hydroperoxides as primary reaction products, (2) a propagation phase where the hydroperoxides formed are decomposed into secondary peroxidation products, and (3) a termination phase involving the formation of tertiary peroxidation products.

LIPID PEROXIDATION: In the current study, analysis of the slowly and rapidly peroxidized lipids compared to the original lipids showed that a high PV accurately indicated a high degree of lipid peroxidation, but a moderate or low PV may be misleading. This is due to the unstable characteristics of hydroperoxides as indicated by the unchanged PV of rapidly peroxidized corn and canola oil compared to their original, unoxidized state. Additional tests which measured secondary peroxidation products (AnV, TBARS, hexanal, HNE and DDE) showed peroxidation differences between the lipid treatments, but similar to PV analysis, these tests also may not provide irrefutable information regarding the amount of peroxidation because secondary peroxidation products are extremely volitile. For the predictive tests, AOM stability accurately reflected the increased lipid peroxidation caused by the slow and rapid peroxidation treatments as indicated by the increased AOM stability value in corn and canola oil, but not in poultry fat and tallow, which indicates a potential disadvantage of the AOM stability test. The OSI assay successfully showed the increased lipid peroxidation caused by slow or rapid peroxidation treatments in all lipids, but it too may have disadvantages similar to AnV, TBARS, hexanal, HNE and DDE, because the OSI assay directly depends on quantification of the volatile secondary peroxidation products. Thus, relative to peroxidation assays utilized in the current study, no individual indicative or predictive test appears to provide a complete assessment of the degree of lipid peroxidation. Therefore, to accurately analyze the amount of lipid damage caused by peroxidation, it may be advantageous to determine the degree of lipid peroxidation at several time points during the peroxidation process using more than one test.

ANIMAL EXPERIMENTATION: Results from this study showed no effect of lipid peroxidation (slow or rapid peroxidation) in corn oil, canola oil, poultry fat or tallow on digestible energy or metabolizable energy content or on apparent total tract digestibility of dry matter, gross energy, ether extract, nitrogen, carbon, and sulfur when fed to nursery pigs. Feeding rapidly oxidized lipids (corn oil and canola oil as well as poultry fat and tallow heated at 185C for 7 h) to nursery pigs for 28 days tended to reduce average daily feed intake and average daily gain compared to pigs fed non-oxidized lipids suggesting that lipid peroxidation can negatively impact pig growth performance. Relative to metabolic oxidation status, feeding slow and rapid peroxidized lipids to nursery pigs increased plasma TBARS concentration. However, feeding peroxidized corn oil, canola oil, poultry fat, or tallow to nursery pigs had no effect on intestinal barrier function as measured by the lactoluse-mannitol protocol utilized in the current study. Lastly, feeding thermally oxidized lipids altered in vivo lipid metabolism by activating the peroxisome proliferator-activated receptor α (PPARα) via up-regulation of some target genes in PPARα, such as acyl CoA oxidase, catalase, and carnitine palmitoyltransferase-1.
Overall the data suggested that feeding thermally-peroxidized lipids to young pigs has little influence on gut barrier function or serum immunity parameters, but may decrease liver triglyceride concentrations, impair metabolic oxidative status, and reduce growth performance, especially if fed lipids containing high concentration of polyunsaturated fatty acids. However, at this point in time, we do not have a clear relationship relating the change in pig performance relative to a defined level of lipid peroxidation. For further information, contact Dr. Brian Kerr, USDA-ARS-NLAE, Ames, IA, by phone (515-294-0224) or email (brian.kerr@ars.usda.gov).