Effects Of Dietary Oxidized Soybean Oil On Lipid Metabolism And Anti-Oxidant Ability In Laying Hens

Sexual mature laying hens have a unique lipid metabolic system which requires large quantity of lipid component in the lipid pool and turnover. Lipid is of great importance for egg formation and the health of laying hens. Dietary addition of oil is one of the most efficient ways to provide essential FAs for laying hens and TG for egg formation, which now attatch much attention in China. However, the unsaturated FAs in vegetable oil were extremely susceptible to peroxidation. Thus, the peroxides brought by dietary oxidized oil are potential hazards which may eventually negatively affect the health status and egg performance of laying hens. The present research used fully mature laying hens as target animals to investigate the influence of dietary oxidized soybean oil on redox status and lipid metabolism of laying hens as reflected by the indices of laying performance, egg quality, activity and mRNA expression of antioxidant enzymes, mRNA expression of apolipoproteins. Furthermore, liver cell culture was used to explore the impact of peroxides on the mRNA expression of the upstream signaling factors. The study includes the following four main parts:Experiment 1. Effect of Dietary Oxidized Oil on Laying Performance and Egg Quality of Laying HensThis experiment focused on the influence of different levels of dietary oxidized soybean oil with different feed duration on laying hen performance and egg quality. The oxidized oil was made by thermally oxidation of food degree soybean oil with aeration. Two hundred and eighty eight 280-d-old Hyline Grey laying hens were randomly allotted to one of four treatments fed with diets containing 0 (NX), 1% (LX), 2% (MX) and 4% (HX) oxidized oil, respectively. Each treatment had 6 replicates with 12 birds each. The feeding trial lasted for 30d, and egg production, ADFI and FCR were recorded or calculated every week and for the whole period. Egg quality indices were measured every week and on d 0. The results showed that MX and HX groups significantly worsen FCR from week 1 (P<0.05). Egg production and the incices of egg quality were not significantly affected (P>0.05). The significant difference of FCR thus came from the changes of ADFI and egg weight which showed trends toward increase and decrease, respectively.Experiment 2. Effect of Dietary Oxidized Oil on Serous and Hepatic Redox Status and the mRNA Expression of Antioxidant Enzymes of Laying HensThis experiment investigated the changes of MDA/ROS accumulation, activity and mRNA expression of antioxidant enzymes in the serum and liver of laying hens. Two hundred and eighty eight 280-d-old Hyline Grey laying hens were randomly allotted to one of four treatments fed with diets containing 0 (NX), 1% (LX), 2% (MX) and 4% (HX) oxidized oil, respectively. Each treatment had 6 replicates with 12 birds each. The feeding trial lasted for 30d. Serum and liver samples were collected on d 0, d 2, d 6, d 14 and d 30 from 1 bird that was randomly chosen from every treatment. The results turned out that the LX group had significantly increased activities of serous and hepatic GPX, SOD and GST (P<0.05), however, these indices were significantlydecreased in the MX and HX groups on d 30 (P<0.05). Dietary soybean oil, no matter fresh or oxidized, significantly increased MDA levels in both serum and liver (P<0.05). MX group significantly increased the expression of antioxidant enzymes (P<0.05), whereas the HX group significantly dereased the expression of GSTs from d 14 (P<0.05).Experiment 3. Effect of Dietary Oxidized Oil on Lipid Metabolism and the Gene Expression of apolipoproteins in the Liver of Laying HensThis experiment was conducted to study the influence of dietary oxidized oil on serous, hepatic and yolk lipid and lipoprotein concentration as well as the mRNA expression of apoB-100 and apoVLDL-II in the liver. The serous concentration of estradiol was also measured. Two hundred and eighty eight 280-d-old Hyline Grey laying hens were randomly allotted to one of four treatments fed with diets containing 0 (NX), 1% (LX), 2% (MX) and 4% (HX) oxidized oil, respectively. Each treatment had 6 replicates with 12 birds each. The feeding trial lasted for 30d. Serum and liver samples were collected on d 0, d 2, d 6, d 14 and d 30 from 1 bird that was randomly chosen from every treatment. Abdominal fat percentage and liver percentage were calculated as soon as the bird was slaughtered. Five eggs were randomly chosen from each replicates for determination of yolk indices. The results showed that abdominal fat percentage and liver percentage were significantly increased in the HX group on d 30 (P<0.05). The serous concentration of VLDL-C was significantly increased in the MX group after d 14 (P<0.05), while that of TG was significantly decreased on d 30. Serous estradiol concentration increased with time in the MX and HX groups. Trans-FA concentration in the yolk increased in the MX and HX groups along with time, whereas the concentration of C18:3n3 decreased with time. The MX group had a significant higher level of hepatice mRNA expression of apoB-100 (P<0.05) on d 30, while on the same day, the HX group significantly increased the expression of apoVLDL-II (P<0.05) and decreased the expression of apoB-100 (P<0.05).Experiment 4. Effect of Different Peroxides on the Expression of Antioxidant and Lipid Metabolism Related Signaling Factors of the Liver Cells of Laying HensLaying hen liver cells were cultured to investigate the effect of oxidized oil, primary peroxide (H₂O₂), and secondary peroxide (HNE) on hepatic expression of PPARα, LXR, Nrf2, SREBP-1 SREBP-2 and related target genes represented by LPL and GSTO1. A concentration of 1.5% was applied for HNE (HNEX) and oxidized oil ethanol extrat (OX) in the culture media to fit the same ROS level of the 0.1mM H₂O₂ as refered in previous studies. There was also a treatment with 1.5% of the fresh oil ethanol extract (FX) for comparison. The culture lasted for 12 h, under the condition of 5%CO2, 37°C. The result showed that the OX and HENX groups significantly increased the expression of SREBP-1 and SREBP (P<0.05). The OX group significantly increased the expression of LXR (P<0.05), while the HNEX group significantly increased the expression of Nrf2 and GSTO1 (P<0.05).