Influence of feeding thermally peroxidized soybean oil on growth performance, digestibility, and gut integrity in finishing pigs

Consumption of peroxidized lipids has been shown to reduce pig performance and energy and lipid digestibility. Objectives of the current study were to evaluate the effect of feeding soybean oil (SO) with different levels of peroxidation on growth performance, lipid, N, and GE digestibility, plasma Trp, and gut integrity in finishing pigs. Fifty-six barrows (46.7 +/- 5.1 kg initial BW) were randomly assigned to one of four diets in each of two dietary phases, containing either 10% fresh SO (22.5 degrees C) or thermally processed SO (45 degrees C for 288 h, 90 degrees C for 72 h, or 180 degrees C for 6 h), each infused with of 15 L/min of air. Peroxide values were 2.0, 17.4, 123.6, and 19.4 mEq/kg; 2,4-decadienal values were 2.07, 1.90, 912.15, and 915.49 mg/kg; and 4-hydroxynonenal concentrations were 0.66, 1.49, 170.48, and 82.80 mg/kg, for the 22.5, 45, 90, and 180 degrees C processed SO, respectively. Pigs were individually housed and fed ad libitum for 81 d to measure growth performance, including a metabolism period to collect urine and feces for determination of GE, lipid, N digestibility, and N retention. Following the last day of fecal and urine collection when pigs were in the metabolism crates, lactulose and mannitol were fed and subsequently measured in the urine to evaluate gut permeability, while markers of oxidative stress were evaluated in plasma, urine, and liver. There were no differences observed in ADFI (P = 0.91), but average daily gain (ADG) and gain: feed G: F were decreased in pigs fed 90 degrees C SO diet (P <= 0.07) compared to pigs fed the other SO diets. Pigs fed the 90 and 180 degrees C SO had the lowest (P = 0.05) DE as a % of GE compared to pigs fed the 22.5 degrees C SO, with pigs fed the 45 degrees C SO being intermediate. Lipid digestibility was similarly affected (P = 0.01) as energy digestibility, but ME as a % of DE was not affected by dietary treatment (P = 0.16). There were no effects of lipid peroxidation on N digested, N retained, or the urinary lactulose: mannitol ratio (P >= 0.25). Pigs fed the SO processed at 90 and 180 degrees 1C had lower concentrations (P < 0.01) of plasma Trp compared to pigs fed the 22.5 and 45 degrees C SO treatments. Pigs fed 90 degrees C SO had the greatest (P < 0.01) concentrations of F 2-isoprostane in plasma and urine thiobarbituric acid reactive substances compared to the other SO treatments. These results indicate that the change in FA composition and/or the presence of lipid peroxidation products in peroxidized SO may reduce ADG, G: F, and digestibility of GE and ether extract, but has little impact on N digestibility and balance or on gut permeability.