Effects Of Lysine On Growth And Development And Intestinal Health Of Broilers And Its Molecular Regulatory Mechanism

Previous studies focused on the lysine requirements and the effects of lysine on the development and growth in broilers.However,the molecular mechanism of dietary lysine regulating the development and growth of broilers is under clear.Based on the relative research situation,the purpose of this experiment was to reveal the molecular mechanism of dietary lysine regulating the chicken growth and intestinal health through evaluating effects of lysine on development,and growth,and the related gene expression of small peptides and amino acid transporter and intestinal barrier of ileum,duodenum and jejunum,and the content of sIgA,and caecum microorganism flora in broiler chickens.Exp 1:Effects of lysine on growth and development and the related genes expression of intestinal protein transporter in broilersThe experimental animals were one-day-old AA broilers of 360,which were randomly assigned to 3 treatment groups with 6 replicates per group and 20 broilers per replicate.Lysine content in LL(lysine deficiency),ML(lysine moderate amount)and HL(lysine excess)groups were 0.60%,1.00%and 1.40%,respectively.The control group was ML group,and the experimental groups were LL group or HL group.The trial period is 3 weeks.The results indicated that:(1)ADG(Average Daily Gain),ADFI(Average Daily Feed Intake),pectoralis weight,thigh weight,abdominal fat weight,pectoralis rate and thigh rate in LL group were significantly lower than ML group(P<0.01),F/G(Feed Gain ratio)of LL was obviously bigger(P<0.01).ADG of HL group was significantly less than ML group(P<0.01).There was no obvious effect on abdominal fat rate in LL or HL groups(P>0.05).(2)Liver weight and gizzard weight in LL group were significantly lower than ML group(P<0.01),heart index and gizzard index in LL group increased significantly more than ML group(P<0.01),and liver weight in HL group was significantly increased(P<0.05).There were no obvious effects on heart weight and liver index in LL or HL groups(P>0.05).(3)The expression levels of PepT1,EAAT3,B~0AT in duodenum and PepT1,B~0AT in ileum of LL were obviously bigger than those of ML(P<0.01),expression levels of CAT1 in duodenum,PepT1,CAT1,EAAT3,B~0AT in jejunum and EAAT3 in ileum of LL were obviously reduced(P<0.01).The expression levels of CAT1 in ileum of LL were obviously cut down(P<0.05).The expression levels of B~0AT,EAAT3 and PepT1 in duodenum and EAAT3,CAT1 in jejunum of HL were obviously reduced(P<0.01).The expression levels of CAT1 in duodenum and B~0AT in ileum in HL group were obviously reduced(P<0.05),the expression levels of PepT1,B~0AT in jejunum and EAAT3 in ileum in HL group were obviously increased(P<0.01).The expression levels of CAT1 in ileum was obviously increased(P<0.05).This results indicated that lysine deficiency may mainly down-regulate the mRNA expression of amino acids and small peptide transporters in jejunum,while excessive lysine may mainly down-regulate the mRNA expression of amino acids and small peptide transporters in duodenum,and affect protein utilization in the body,which may further significantly inhibit the growth and development of broilers.Exp 2:Effects of lysine on immune organs and intestinal immunity in broilersThe experiment design is the same as exp 1.The results indicated as follows:(1)LL group significantly decreased spleen weight(P<0.01)and thymus weight(P<0.05),and bursa of fabricius index significantly increased(P<0.01),while HL group had no obvious effect on immune organ development of broilers(P>0.05)compared with ML.(2)Compared with ML,the content of sIgA(secretory immunoglobulin A)in duodenum,ileum and jejunum of LL group was obviously reduced(P<0.01),the content of sIgA in duodenum and ileum of HL group was obviously reduced(P<0.01),and the content of sIgA in jejunum was obviously lowered(P<0.05).(3)LL group obviously decreased the expression of Claudin-1of duodenum,ZO-1,Occludin,Claudin-1 of jejunum,and ZO-1,Claudin-1 of ileum(P<0.01),significantly lowered the gene expression of ZO-1 in duodenum(P<0.05),and significantly increased the mRNA expression of Occludin in duodenum and ileum(P<0.01).HL group significantly increased ZO-1 and Occludin in duodenum,Occludin mRNA expression in jejunum(P<0.01),significantly lowered ZO-1 and Claudin-1 in jejunum,ZO-1mRNA expression in ileum(P<0.01),and significantly lowered Claudin-1 mRNA expression in ileum(P<0.05).(4)Compared with ML,LL group significantly increased TNF-αin duodenum and ileum,INF-γmRNA expression in jejunum(P<0.01),significantly lowered IL-10 and TNF-αin jejunum,IL-10,INF-γand IL-12 mRNA expression in ileum of broilers(P<0.01).HL group significantly increased the mRNA expression of IL-10 in duodenum(P<0.05),significantly increased the mRNA expression of TNF-αin duodenum and jejunum(P<0.01),significantly lowered the mRNA expressions of IFN-γand IL-10 in jejunum,IL-10 and IL-12 in ileum(P<0.01).In conclusion,lysine deficiency may mainly affect the expression of physical and chemical immune barriers related genes in jejunum and reduce the content of small intestine sIgA and the development of immune organs of broilers,while lysine excess may mainly affect the expression of physical and chemical immune barriers related genes in jejunum and ileum and reduce the content of small intestine sIgA,thereby affecting the intestinal barrier and reducing the immune function of broilers.Exp 3:Effects of lysine deficiency on cecal microflora in broilersThe experimental animals were one-day-old AA broilers of 240,which were randomly assigned to 2 treatment with 6 replicates per treatment and 20 broilers per replicate.Lysine content in the 2 treatment were 0.60%(lysine deficient group,D0 group)and 1.00%(lysine moderate group,C0 group),respectively,using a single factor design.The trial period is 3weeks.The results indicated that:(1)Alpha diversity index of D0 group had no obvious change(P>0.05),while microbial community structure of D0 group had significant difference(P<0.05)compared with C0 group.(2)Compared with C0,the abundance of Alphaproteobacteria in D0 group were significantly lowered(P<0.05),and the abundance of Bacteroides＿uniformis was obviously lowered(P<0.05),and the abundance of Tyzzerella was obviously increased(P<0.05).In conclusion,lysine deficiency may mainly affect the structure of microbial community and the abundance of intestinal flora,may lead to reduce intestinal barrier function of broilers,imbalance of cecal flora,and reduce immune function of broilers,which may hinder the development and growth of broilers.