Effects Of Low Methionine On Production Performance And Antioxidant Capacity Of Laying Hens In Late Laying Period

This experiment was conducted to study the effects of low methionine on production performance,methionine metabolism and antioxidant capacity of laying hens in late laying period.Based on the egg production,a total of 180 laying hens(Grey Hyline,62 weeks old)were allocated to 3 groups with 6 replicates each.Three groups were fed different dietary which contained 0.21%(high level low methionine group,HD group),0.27%(low methionine group,D group)and 0.33%(control group,C group)methionine,and the experiment period was 90 days.The main results showed as follows:1.Effects of low methionine on production performance,egg quality traits and serum biochemical indexes of laying hens(1)Dietary low methionine significantly reduced the average daily feed intake,egg production,egg mass,egg weight and unqualified rate of eggs,and improved feed/egg ratio of laying hens(P<0.05);(2)Low methionine significantly affect egg shape index,eggshell thickness,eggshell strength,egg yolk color and egg albumen ratio(P<0.05),but have no effect on eggshell ratio,egg yolk ratio,egg albumen and yolk solid content and haugh units(P>0.05).The egg shape index of D group the the group was higher than that of HD group(P<0.05).The eggshell thickness of HD group was higher than other two groups(P<0.05).The eggshell strength of D group was higher than C group,and the yolk color of D group was higher than other two groups(P<0.05).The egg albumen ratio increased with the increase of dietary methionine level(P<0.05),but egg albumen solid content was no changed.(3)Low methionine significantly affect serum calcium(Ca),uric acid(UA),albumin(ALB),triglyceride(TG)and alkaline phosphatase(ALP)content(P<0.05).The C group got lowest serum ALP activity and highest calcium and TG content(P<0.05).The ALB of HD group was lowest(P<0.05).The serum UA level increased with the increase of dietary methionine level(P<0.05).In conclusion,dietary low methionine reduced egg production,egg mass,egg weigh,and increased egg-feed ratio.Dietary low methionine have significantly influence on the egg quality traits which reduced egg albumen ratio and increased eggshell strength and thickness.The change of serum ALP,ALB,UA,TG,Ca,P content means low methionine affect the metabolism of layers.2.Effects of low methionine on serum free amino acid content and gene expression of methionine metabolism related genes in liver of laying hens(1)Low methionine significantly reduced the content of methionine in serum of laying hens(P<0.05).The levels of serum serine,glycine,alanine and orn of 0.21% group were significant higher than other two groups,but the change of serum cysteine content contrarily(P<0.05).The levels of serum valine,isoleucine,phenylalanine,arginine and proline of 0.27% group were significant lower than control group(P<0.05).The levels of serum a-AAA and EOHNH2 of 0.21% group were significant higher than 0.33% group,but b-Ai BA and 3Mehis were significant lower than 0.33% group(P<0.05).(2)The relative expression of DNA methyltransferase 1(Dnmt1),DNA methyltransferase 3 alpha(Dnmt3a),N6-adenosine-methyltransferase subunit 3(METTL3)and methyltransferase like 14(METTL14)in the liver of 0.21% group were significant improved,and the relative expression of METTL3 in the liver of 0.27% group were also significant improved compared with control group(P<0.05).The relative expression of methionine adenosyltransferase 1A(MAT1A),cystathionine-betasynthase(CBS)and 5-methyltetrahydrofolate-homocysteine methyltransferase(MTR)in the liver of 0.21% group were significant improved,and the relative expression of MTR in the liver of 0.27% group were also significant improved compared with control group(P<0.05).Low methionine have no influence on the relative expression of adenosylhomocysteinas(Ahcy)and Betaine homocysteine methyltransferase(BHMT)gene.In conclusion,high levels of low methionine significantly increased the expression levels of Dnmt1,Dnmt3 a,METTL3 and METTL14,which may affect the methylation of DNA and RNA.Low methionine decreased serum methionine and cysteine content and improved the expression quantity of MTR gene as well as the serum content of glycine and serine which may affect the resynthesis of methionine and sulfonium way.2.Effects of low methionine on antioxidant index in serum and liver and gene expression of antioxidant genes in liver of laying hens(1)Low methionine significantly affected serum CAT,GSH-Px,MDA and GSH level(P<0.05).The activity of CAT in C group was higher than other two group(P<0.05).The activity of GSH-Px increased with the increase of dietary methionine level(P<0.05).The MDA content of C group was lower than HD group,and GSH content was higher than HD group(P<0.05).(2)Dietary low methionine significantly affected GSH-Px activity and GSH content in liver(P<0.05).The GSH-Px activity of HD group was higher than other two groups(P<0.05).The content of GSH decreased with the decrease of methionine(P<0.05).(3)Dietary low methionine significantly affected the expression of SOD,CAT,GPX1,GPX2,GPX3 and MsrA in the liver(P<0.05).The expression of CAT,GPX1 and GPX3 in liver of C group was significantly lower than that of HD group(P<0.05).The expression of GPX1 and Msr A in liver of HD group was significantly higher than 0.27% and C group(P<0.05).In conclusion,low methionine significantly affected the redox status of hens by glutathione system.Dietary low methionine significantly reduced serum CAT and GSH-Px activity and GSH content and increased serum MDA.Low methionine significantly reduced GSH-Px activity and GSH content in the liver.At the same time,high levels of low methionine significantly increased the expression of CAT,GPX1,GPX2,GPX3 and MsrA in the liver in order to maintain the health of laying hens.