The Construction Of Egg Production Model And The Mechanism Of Lipid Metabolism Mediated By AMPK Pathway Affecting Egg Production In Muscovy Duck

The aim of this study was to establish an egg production model,analyze the differencesin liver metabolite profiles and the gene expression of AMP-activated protein kinase(AMPK)signaling pathway in liver and abdominal fat of Muscovy duck at different egg-laying stages,so as to provide egg selection model at early breeding stage and illustrate the mechanism of lipid metabolism in response to egg laying.A total of 300healthy female Muscovy ducks were selected,and body size and egg production of each duck were recorded in pre-laying(22 weeks,TW group),early-laying(30 weeks,TH group),laying(40 weeks,FO group),and post-laying(60 weeks,SI group)stages.Fifteen Muscovy ducks were randomly selected from each stage for blood,liver,abdominal fat,follicle collection.Serum lipid levels were determined by automatic biochemical analyzer,hormone levels were measured by radioimmunoassay,histological structure of the liver,abdominal fat and follicles were observed by hematoxylin-eosin(HE)staining and Oil Red O staining,the fatty acid composition of liver,abdominal fat and follicle was measured by gas chromatography-mass spectrometry(GC-MS),liver metabolite profiles were determined by ultra-high-performance liquid chromatography-electrospray mass spectrometry(UPLC-MS),and AMPK pathway gene expression of liver and abdominal fat was determined by quantitative real-time PCR(q RT-PCR).The results were as follows:1.Analysis of the levels of serum lipids and hormone,and histological structure and fatty acid composition of liver,abdominal fat,and follicular at different egg-laying stages The levels of total cholesterol(TC),low-density lipoprotein cholesterol(LDL-C),triglyceride(TG),and very low-density lipoprotein cholesterol(VLDL-C)at 40 weeks were significantly higher than those at 22,30,and 60 weeks.The levels of high-density lipoprotein cholesterol(HDL-C)at 30 and 40 weeks were significantly lower than those at22 and 60 weeks(P<0.05).The levels of follicle-stimulating hormone(FSH)and estradiol(E2)at 40 weeks were significantly higher than those at 22 and 60 weeks(P<0.05).However,there were no significant differences in the levels of luteinizing hormone(LH),prolactin(PRL),and progesterone(P)at different egg-laying stages.The reticular formation of the liver was intact at 22 weeks,and lipid deposition significantly increased at 40 and 60 weeks.Liver saturated fatty acids(SFA),monounsaturated fatty acids(MUFA),and polyunsaturated fatty acids(PUFA)were mainly composed of C16:0,C18:0,C18:1,and C20:2 n-6,accounted for 32%,16%,30%,and 9%of the total fatty acids,respectively.The volume of adipocytes was larger at 60 weeks with a significantly lower number per unit than that of 22 weeks(P<0.05).Abdominal fat SFA,MUFA,and PUFA were mainly composed of C16:0,C18:1,and C22:5 n-3,accounted for30%,40%,and 6%of the total fatty acids,respectively.The follicular granular layer thickness of the F7 follicle was the thinnest,and was most thick at the F1-F3 follicle.The follicular theca layer thickness of SWF was the thinnest.Follicular SFA,MUFA,and PUFA were mainly composed of C16:0,C18:1,and C20:5 n-3.2.Construction of egg production model of Muscovy duckMultiple linear regression was used to analyze the relationship between abdominal fat weight,body weight,and body size of Muscovy duck,and the abdominal fat rate model at30 weeks was established as Y(abdominal fat rate)=﹣0.735-0.0009×body weight+0.0097×semi diving length+0.0152×keel length+0.017×the age of initial egg laying(R~2=0.715,P<0.05).Multiple linear regression was used again to construct the prediction model for egg production of Muscovy Duck at 40 weeks as Y(egg production)=204.48-0.01×body weight+0.592×keel length-0.538×the age of initial egg laying-0.461×abdominal fat weight(R~2=0.405,P<0.01).3.Analysis of nontargeted metabolomics in liver and AMPK pathway gene expression in liver and abdominal fat at different egg-laying stagesIn FO/TW group and SI/FO group,324 and 332 differential metabolites were selected respectively.The differential metabolites were mainly enriched in the pathways of amino acid metabolism,glycerophospholipid metabolism,nucleotide metabolism,vitamin metabolism.The liver provides amino acids,lipids,nucleotides,vitamins,and choline,and so on,which are essential materials for yolk precursor synthesis.Gene AMPKα1 was in a low expression level in liver and abdominal fat at 22,30,40,and 60 weeks,and was significantly lower than the expression of FAS at different egg-laying stages.Gene FAS was expressed in a significantly high level in the liver at 22,40,and 60 weeks.The expression levels of HMGR,HNF4α,ACC1,and SREBP1c at 40weeks were significantly higher than those at 22 and 30 weeks(P<0.05)in the liver.The expression levels of HMGR and ACC1 at 40 weeks were significantly higher than those at60 weeks in abdominal fat.The expression level of CPT1 at 30 weeks was significantly higher than those at 22 and 60 weeks(P<0.05)in abdominal fat.The increased levels of FSH and E2 during egg laying promoted the synthesis of serum lipids,and increased lipid deposition in liver and abdominal fat,thus promoted follicle development.The constructed multiple linear regression model could be used to evaluate the egg laying of 40 weeks of Muscovy Duck for its early selection.The up-regulated FAS gene expression in liver and abdominal fat through AMPK pathway promoted synthesis of fatty acids.