| The intestinal mucosa is the main part of absorbing nutrients and the first line of defense against the invasion of pathogenic microorganisms.Its structure and function are highly susceptible to the influence of in vivo factors and intestinal cavity environmental factors.However,the mechanism by which in vivo factors melatonin and intestinal environmental factors intestinal microbes affect the structure and function of intestinal mucosa in layers is still unclear.The present study mainly focued on the effects of in vivo factors(melatonin)and environmental factors(intestinal microbes)on the intestinal mucosal structure and function in laying hens.The conclusion will provide new methods and new ideas for improving the performance and egg quality of laying hens in poultry industry.1.The promotion mechanism of melatonin on laying performanceThe prerequisite for laying hens to produce a large number of eggs in the laying peak period is the efficient absorption of nutrients,especially amino acids,by the intestinal mucosa.A large number of studies have confirmed that melatonin feeding could improve the performance of laying hens.However,the mechanism of how melatonin improves egg production performance is unclear.In this study,laying hens were fed with melatonin at different doses(0.625 mg/kg diet、2.5 mg/kg diet、10 mg/kg diet)for two consecutive weeks.The results showed that,compared with the control group,feeding 0.625 mg MEL/kg diet could increase laying rate,eggshell thickness,albumen height.At the same time,feeding 0.625 and 2.5 mg MEL/kg diet could significantly increase the levels of various amino acids such as aspartic acid,threonine,and serine in serum.Analysis of the amino acid transporters expression in the intestinal mucosa showed that 0.625 mg MEL/kg diet could significantly increase the mRNA expression of PepTl,B0AT,b0.+AT and EAAT3 in the jejunum.In cultured intestinal "organoids",0.5 μM melatonin treatment can significantly increase the mRNA expression of PepTl,b0.+AT and EAAT3.In order to study the pathway of melatonin act on intestinal mucosa,we used high-performance liquid chromatography(HPLC)to analyze the concentration of melatonin in serum and intestinal fluid.The results showed that low dose(0.625 mg MEL/kg diet)melatonin could locally promote the mRNA expression of intestinal antioxidant enzymes(GPx-3,SOD-1 and PRDX-3).In summary,our results indicate that melatonin could upregulate the expression of antioxidant enzymes in the intestine,thereby promoting the expression and function of amino acid transporters in the intestinal mucosa,and ultimately improving laying performance and egg quality.2.The regulation mechanism of intestinal microbial on the intestinal mucosal structure and function in laying hens.Ninghai Yellow Hens is an excellent local chicken breed in Zhejiang province.It is a meat and egg dual-use breed.It has the advantages of stable production performance,strong disease resistance,delicious meat,strong adaptability and other advantages that HyLine Hens does not have.Since intestinal mucosa is important for poultry production performance,in the present study,we analyzed the morphological difference of intestinal mucosa between Ninghai Yellow Hens and HyLine Hens,and the results showed that there presented a large number of wrinkles in the intestinal villi of Ninghai Yellow Hens,and the number of duodenal villus wrinkles and the circumference of the villi were higher by 800.52%and 43.67%than that of the HyLine Hens at the same age.The analysis of duodenal amino acid transporter expression showed that,Ninghai Yellow Hens had higher abundances of PepTl,B+AT,b0.+ AT and EAAT3 compared with HyLine Hens.These indicated that the intestinal mucosa of Ninghai Yellow Hens has a larger absorption area and a stronger amino acid transport function when compared with HyLine Hens.We further analyzed the density and function of goblet cells in the dundenal mucosa,the results showed that,compared with HyLine Hens,significantly higher density of goblet cells and MUC2 were presented in the duodenum of Ninghai Yellow Hens.This suggested that the intestinal mucosal barrier function of Ninghai Yellow Hens is stronger than that of HyLine Hens.We further illustrate the developmental profile of the special intestinal mucosal structure and function in Ninghai Yellow Hens with different ages.The results showed that compared with the pre-laying period and the post-laying period,the amount of villous wrinkles in the small intestine of Ninghai Yellow Hens in laying peak period was higher,and the duodenum was the highest.The results of 16s rDNA sequencing showed that the bacterial community were significantly different among three ages,and the relative abundance of Lactobacillus in Ninghai Yellow Hens in the laying peak period was significantly higher than the pre-laying period and the late laying period,among which L.intestinalis,L.ingluviei,L.agilis,L.salivarius and L.aviarius were the top five Lactobacillus.To further confirm the influence of intestinal microbes on the intestinal mucosal structure and function,Ninghai Yellow Hens in laying peak period were fed with multiple-antibiotics.The results showed that,compared with the control group,the number of duodenal villous wrinkles decreased by 15.54%,goblet cell density decreased by 105.10%,MUC2 expression decreased by 145.38%,and the expression of intestinal mucosal amino acid transporters PepTl and B0AT were significantly reduced by 289.84%and 77.78%,respectively.In summary,our results showed that intestinal microbes(mainly Lactobacillus)could effectively improve the intestinal mucosal absorption area,amino acid absorption capacity and barrier function.3.ConclusionFeeding low-dose melatonin(0.625 mg MEL/kg diet)can increase the expression of local antioxidant enzymes in the intestine of laying hens,thereby promoting the expression and transport function of amino acid transporters in the intestinal mucosa,and ultimately improving egg production performance and egg quality of laying hens;at the same time,intestinal microorganisms(mainly Lactobacillus)can effectively improve the absorption area,amino acid absorption capacity and barrier function of the intestinal mucosa of laying hens during egg production.In summary,in vivo factors MEL and intestinal environmental factors Lactobacillus can regulate the structure and function of intestinal mucosa. |
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