| The study was conducted to determine the effects of chitosan on lipid metabolism and the underlying mechanism in laying breeders. Four hundred and fifty 26-weeks-old Hy-Line brown laying breeders were randomly assigned to 5 groups with 6 replicates in each group and each replicate contained 15 chickens. Chickens in 5 groups were fed experimental diets containing 0(control),250,500,1000 and 2000 mg/kg chitosan, respectively. The trial lasted for 8 weeks. The objective of the experiment 1 was to elucidate the effects of chitosan on production performance and fatty acid composition of egg yolk.In the experiment 2, lipid content, adipocytokine and hormone Levels,and the activity of enzymes in serum related to lipid metabolism were detected to illustrate the regulation mechanism of chitosan on lipid metabolism.The experiment 3 and 4 were conducted to investigate the effects of chitosan on relative expression of genes and proteins related to lipid metabolism,in order to establish the molecular regulation mechanism of chitosan on lipid metabolism.The results of this study showed as follows:(1)Effect of chitosan on production performance(Laying performance and reproductive performance) of laying breeders were in dose-dependent relationship. The dietary chitosan of lower dose(250mg/kg and 500mg/kg) could promote the production performance of laying breeders,but the promotion effects of higher dose chitosan(1000mg/kg and 2000mg/kg) were weakened.(2)Effect of chitosan on fatty acids profile of egg yolk were in dose-dependent relationship.Lower dose chitosan decreased the content of SFA and the ratio of n6 to n3 in egg yolk, and increased the levels of n-3PUF, PUFA, n-6PUFA and MUFA.With the increase of supplemental dose,the ability of chitosan to improve the quality of egg yolk was decreased.(3)Effect of chitosan on the content of free fatty acids(FFA) in liver and serum was in a dose-dependent relationship.The dietary chitosan of lower dose(250mg/kg and 500mg/kg) could reduce the content of FFA,but the increase of supplemental dose caused a rise in the content of FFA.(4)Chitosan regulated the concentration of very low density lipoprotein(VLDL) in blood.The VLDL concentration of 250mg/kg chitosan group was 0.45mmol/L, corresponding to the best laying performance.(5)Effect of chitosan on the levels of leptin, growth hormone(GH) and insulin were in dose-dependent relationship.Lower dose chitosan (250mg/kg and 500mg/kg) decreased the levels of leptin in serum and increased GH and insulin levels.With the increase of supplemental dose,the concentration of leptin was increased,the levels of GH and insulin were decreased in different degrees.(6)Effect of chitosan on the activities of lipid metabolism-related enzymes were in dose-dependent relationship.The dietary chitosan of lower dose(250mg/kg and 500mg/kg) elevated the activities of ACC1,ME,SCD1,DGAT1 in liver,and induced the activities of HMGR in liver,HSL in abdominal fat,LPL in serum.With the increase of supplemental dose,the activities of ACC1,ME,SCD1 and DGAT1 were decreased,while the activities of HMGR, HSL and LPL were increased(7)Effect of chitosan on the gene expression of ACC1,FAS,ME and SCD1 were in dose-dependent relationship.The dietary chitosan of lower dose(250mg/kg and 500mg/kg) could promote the expression of genes related to fatty acid synthesis,but the promotion effects of higher dose chitosan were weakened.(8)The dietary chitosan of lower dose(250mg/kg and 500mg/kg) could promote the expression of proteins related to fatty acid synthesis,but the promotion effects of higher dose chitosan were weakened.(9)Taking all these results into consideration,the optimum dosage of chitosan in laying breeder diet was 250-500mg/kgIn summary, the addition of chitosan significantly affected the production performance and lipid metabolism of laying breeders, and there was dose-dependent effect.The dietary chitosan of lower dose(250mg/kg and 500mg/kg) regulated the content of FFA and VLDL, limited the excessive accumulation of TG in the liver, by reducing HSL activity in the abdominal fat and improving DGATl activity in the liver.The dietary chitosan of lower dose(250mg/kg and 500mg/kg) regulated the gene expression and the enzyme activity related to fatty acid synthesis,and promoted fatty acids synthesis in liver by reducing the levels of leptin, increasing GH and insulin levels, and improving the expression of PPARy and SREBP-lc.In addition,Chitosan increased the synthesis of MUFA and reduced cholesterol synthesis in the liver by improving the activity of SCD1 and reducing the activity of HMGR, respectively. In summary, the addition of chitosan could promote the synthesis of fatty acids in liver and regulate the lipid metabolism of laying breeder and fatty acid composition of egg yolk,which made it possible to produce eggs with high polyunsaturated fatty acids content. |
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