Influence of Thermally Peroxidized Soybean Oil on Growth Performance and Oxidative Status in Growing Pigs

The objective of this study was to evaluate the effect of feeding peroxidized soybean oil (SO) on growth performance and oxidative status in growing pigs. Fifty-six barrows (25.3 ± 3.3 kg initial BW) were randomly assigned to one of four diets containing either 10% fresh SO (22.5^oC) or SO exposed to heat (45^oC for 288 h, 90^oC for 72 h, or 180^oC for 6 h), each with an air infusion of 15 L/min. Peroxide values for the 22.5, 45, 90 and 180^oC processed SO were 2.0, 96, 145, and 4.0 mEq/kg, respectively. Anisidine values for 22.5, 45, 90 and 180^oC processed SO were 1.2, 8.4, 261, and 174, respectively. Pigs were individually housed and fed ad libitum for 49 d to measure growth performance, including a metabolism period to collect urine and serum for analysis of oxidative stress markers. Oxidative stress markers included serum and urinary thiobarbituric acid reactive species (TBARS) and urinary F₂-isoprostanes (ISP) as markers of lipid damage, serum protein carbonyls (PC) as a marker of protein damage, and urinary 8-hydroxy-2'-deoxyguanosine (8-OH-2dG) as a marker of DNA damage. Glutathione peroxidase activity (GPx) was measured in serum and ferric reducing antioxidant potential (FRAP) was measured in urine as determinants of antioxidant status. Although there were no differences in final BW 70.8 ± 5.7 kg (P = 0.11) and ADFI (P = 0.19), ADG was decreased in pigs fed 90^oC SO diet (P = 0.01), while G:F was increased (P = 0.02), in pigs fed 45^oC SO diet compared to the other SO diets. Compared to the other treatments, urinary ISP was increased in pigs fed the 90^oC SO diet (P = 0.02), while pigs fed the 45^oC SO diet had increased urinary TBARS (P = 0.02), with no differences found in urinary FRAP and 8-OH-2dG. Dietary lipid peroxidation had no effect on serum TBARS (P = 0.51); however, pigs fed the 90^oC SO diet had significantly higher serum PC (P = 0.01) compared to the other SO diets. In addition, pigs fed the 90^oC and 180^oC SO diets had significantly lower serum GPx (P = 0.01) in comparison to the 22.5^oC and 45^oC SO diets. The presence of peroxidation compounds as measured by PV and AnV found in the 90^oC SO diet were shown to decrease performance by reducing ADG and metabolically inducing oxidative stress by increasing urinary ISP and TBARS and increasing serum PC while diminishing serum GPx.