Disorder Of Lipid Metabolism In Broiler Caused By Stress And The Rescuing Effect Of NCG On Fatty Liver Induced By Corticoisterone In Broilers

Stress response is the process of destruction and recovery of the physiological balance in the body.This process relies on the activation of the sympathetic nervous system(ANS)and the hypothalamic-pituitary-adrenal gland(HPA)axis and involves a series of endocrine adjustments.Glucocorticoids(GCs)released by adrenal cortex is essential to maintain the stability of the internal environment,and the main glucocorticoid for fowls is corticosterone(CORT).In birds,the duration of tonic immobility(TI)can be used as the indicator of stress response,and birds can be divided into short TI and STI phenotye depending on TI duration.LTI birds is commonly considered as higher response to stress than STI counterparts.There is a strong correlation between stress response and lipid metabolism.In chicken,the liver is the main site for lipids metabolism.It's well established that consecutive injection of CORT induces fatty liver in chicken.Functional amino acids act not only as precursors for protein synthesis but as important regulators of metabolism in the body.It means that functional amino acids are not only necessary for the normal growth and maintenance of animals,but also for the synthesis of a variety of bioactive substances.However,till now it's still unknown that the effects of functional amino acids on regulating lipids metabolism.Therefore,the objectives of this study include:1)the difference of lipids metabolism between different TI(Tonic immobility,TI)phenotypes;2)The effect of NCG supplemented in diet on alleviating the fatty lifer induced by CORT injection in broilers.1 Effects of Different TI Phenotypes on Lipid Metabolism in BroilersA total of 500 1-day-old Rose 308 broilers were randomly selected to be induced into different TI phenotypes on the 11th,18th and 26th day respectively according to the standard procedure of white feather broiler chickens.The broilers were divided into a short TI group(STI)and a long TI group(LTI).The concentrations of TG and TCH in plasma and tissues were measured by biochemical analysis.The expression of genes involved in lipid and cholesterol metabolism in the liver and leg muscle were detected by real-time quantitative PCR.Western blot(WB)was used to detect the expression of proteins involved in this process.The results showed that TI phenotypes had no effect on plasma TG concentration in broilers(P>0.05),while the concentration of TG in the liver of LTI broilers was higher than that in STI broilers,and the difference of hepatic TCH content reached the statistical significance(P<0.05).The level of TG and TCH in leg muscle of LTI broiler were significantly higher than that of STI broiler(P<0.01).Real-time PCR results showed that expression of genes including ACC,CPT-1,PPARa and LPL mRNA in the liver of LTI broilers were significantly lower than STI(P<0.05),and FAS mRNA expression showed a tendency to decrease in LTI compared to STI(0.05<P<0.1).With respect to CPT-1 enzyme activity,LTI broilers showed a significant decrease in the liver than STI(P<0.01).In leg muscle,genes expression related to lipid and cholesterol metabolism were generally up-regulated in LTI compared to STI(P<0.05),as well as significantly higher expression of GR(P<0.01).Western blot results showed that protein expression of SCD-1 and CD36 in leg muscle of LTI broilers was significantly higher than STI(P<0.05;P<0.01),while SREBP1 showed a lower expression(P<0.05).TI phenotypes had no effect on proteins expression related to cholesterol metabolism,while CYP27A1 in leg muscle of LTI broilers was significantly lower than STI(P<0.05).2 Effects of NCG on fatty liver induced by corticosteronein broilersIn this study,100 1-day-old Lihua broilers were used and divided into six groups:the control group(CON group,n=11),corticosterone injection group(T group,n=11),low concentration(0.1%)of NCG group(N2 group,n=13),low concentration(0.1%)of NCG diet with corticosterone injection group(N2T group,n=13),high concentration(0.2%)of NCG diet group(N4 group,n=13)and high concentration(0.2%)of NCG diet with corticosterone injection group(N4T group,n=13).Corticosterone injection was conducted on the 28th day for seven days.Functional amino acid was supplemented into the basal diet during the whole experiment.The biochemical indexes in plasma and tissues were detected by biochemical analysis.Real-time quantitative PCR were used to detect the expression of fat metabolism in liver and leg muscle.The results showed that exogenous corticosterone injection significantly decreased the endogeneous corticosterone secretion(P<0.01),while NCG did not affect plasma CORT concentration(P>0.05).Corticosterone treatment significantly reduced the body weight of broilers(P<0.05),increasing abdominal fat deposition and the relative weight of liver to body weight(P<0.05),and significantly decreased the weight of immune organs(P<0.01).NCG had no effect on organs development,while NCG could significantly alleviate CORT-induced enlargement of liver(P<0.05)and decrease liver weight.Fatty liver disease was also confirmed by higher level of plasma TG(P<0.01)concentration compared to CON group,corticosterone treatment significantly increased TG concentration in the liver and leg muscle(P<0.01),NCG significantly reduced corticosterone-induced increase of TG in plasma and tissues(P<0.01).Real-time PCR results showed that expression of genes including ACC,FAS,SCD-1 and SREBP-1 mRNA in the liver were significantly up-regulated by corticosterone treatment(P<0.01),and the expression of LPL mRNA in the liver was significantly down-regulated(P<0.01).NCG could significantly reduce the expression of FAS and LPL mRNA(P<0.01),while the expression of ACC,SCD-1 and SREBP-1 mRNA were not affected.Corticosterone treatment significantly upregulated the expression of FAS,SCD-1 and SREBP-1 mRNA in leg muscle(P<0.01),NCG treatment significantly down-regulated the expression of FAS and SREBP-1 mRNA(P<0.05),and had no effect on expression of SCD-1 mRNA.Corticosterone treatment had no effect on the expression of CPT-1 and CD36.NCG could significantly up-regulate the expression of CPT-1 and CD36 mRNA(P<0.01),and there was no interaction between NCG and CORT.The concentration of TG and TCH in the liver and leg muscle of LTI broilers were higher than that in STI broilers,supplementation with NCG in diet could markedly alleviate fatty liver disease induced by corticosterone.