| The purpose of this experiment was to study the effects and mechanisms of gallic acid on the growth performance,organ index,cytokines,immunoglobulins,intestinal morphology and intestinal flora of rapidly-growing yellow-feathered broilers infected with avian pathogenic E.coli O78(APEC O78).To study the effect of adding different doses of APEC O78 challenge,360 1-day-old yellow-feather broiler male chicks with the same body weight basically,were selected and randomly divided into 6 treatment groups with 6 replicates in each group and 10 in each replicate in the experiment 1.The 6 treatment groups were control group(basic diet),attack group(basic diet),antibiotic group(basic diet + 200 mg/kg chlortetracycline),GA100group(basic diet + 100 mg/ kg gallic acid),GA200 group(basic diet + 200 mg/kg gallic acid),and GA300 group(basic diet + 300 mg/kg gallic acid).The whole experiment period was 28 days,of which 1-14 days was the normal feeding period and from the 14 th day,the remaining groups was artificially infected with E.coli for three consecutive days,except for the control group.In the experiment 2,the APEC O78 as the research object to explore the effects of subinhibitory concentration of gallic acid on its growth,biofilm formation and adhesion strength,as well as the metabolism and transcription function.The results of experiment 1 showed that:(1)Compared with the control group,the ADFI and F/G of the attack group increased significantly from 15-28 days(P<0.05);the addition of different doses of gallic acid can significantly reduce ADFI and F/G compared with the attack group /G(P<0.05),the F/G in the GA200 group was the lowest,but there was no significant difference from the antibiotic group(P>0.05).(2)Compared with the control group,the attack group significantly increased the bursal index of 28 days old(P<0.05);the GA100 group and antibiotic group significantly lowered the bursal index of the attack group(P<0.05);Compared with the attack group,GA100 group,GA200 group and GA300 group,the antibiotic group significantly improved the spleen index(P<0.05).(3)At the age of 19 days,compared with the control group,the attack group significantly increased the levels of serum IL-1β,IL-6,IL-8,TNF-α and IFN-γ(P<0.05);and Compared with the attack group,the GA200 group can significantly reduce the levels of IL-1β,IL-6,IL-10,and IFN-γ(P<0.05),and the GA100 and GA300 groups significantly reduced the levels of IL-6(P<0.05),the antibiotic group significantly reduced the level of IL-10(P<0.05).At 28 days of age,compared with the control group,the attack group significantly reduced the level of IL-10(P<0.05);compared with the control group,the GA100 group,GA200 group,GA300 group and antibiotic group could significantly increase the level of IL-10 IL-10 levels(P<0.05),and the GA100 group,GA300 group and antibiotic group also significantly reduced IL-8 levels(P<0.05).(4)At the age of 19 days,compared with the control group,the attack group significantly increased the serum Ig A,Ig G and Ig M levels(P<0.05);compared with the attack group,the GA100,GA200,GA300 and GA300 groups The antibiotic group significantly reduced the content of Ig A(P<0.05);At 28 days of age,compared with the attack group,the antibiotic group significantly increased the content of Ig G,and the GA100 group significantly increased the content of Ig M(P<0.05).(5)At the age of 19 days,compared with the control group,the attack group significantly reduced the villus height of the jejunum and ileum,increased the depth of the jejunal crypts,decreased the crypt depth of the ileum,and also significantly reduced the jejunal VCR(P<0.05);Compared with the attack group,the GA100,GA200,GA300 and antibiotic groups can significantly increase the height of jejunal villi and the VCR of jejunum(P<0.05),and also significantly increased the height and hiding of ileal villi,and the depth of the fossa(P<0.05).At 28 days of age,compared with the control group,the attack group significantly increased the jejunal crypt depth,ileal villus height,and crypt depth(P<0.05),and significantly reduced the VCR of the jejunum and ileum(P<0.05);Compared with the attack group,the GA300 group and the antibiotic group significantly increased the jejunal villus height and crypt depth(P<0.05),and significantly increased the jejunal VCR(P<0.05)compared with the GA100 group and the GA200 group;Compared with the attack group and the antibiotic group,the GA100 group,GA200 group and GA300 group significantly increased the height of ileal villi and VCR(P<0.05).(6)The 16 S r RNA sequencing results showed that compared with the attack group and the antibiotic group,the GA100,GA200 and GA300 groups can promote the growth of Lactobacillus and inhibit the reproduction of Shigella attack group.It also improved the structure of the jejunal intestinal flora,but had no significant effect on the structure of the cecal intestinal flora.The results of experiment 2 showed that:(1)The results of MIC of gallic acid to APEC O78 was 4 mg/m L,and gallic acid can significantly inhibited the formation ability and adhesion rate of E.coli biofilm.(2)Sub-MIC concentration(2 mg/m L)can significantly affect the arginine biosynthesis of APEC O78,the metabolism of alanine,aspartic acid and glutamate and bacterial quorum sensing,as well as the metabolism of propionic acid.In summary,gallic acid can maintain the growth performance of yellow-feather broilers after E.coli challenge,increase the content of immunoglobulin,and reduce the level of proinflammatory cytokines.In addition,gallic acid can also affect the amino acids metabolic pathway of E.coli O78,indirectly affects the synthesis of bacterial protein achieving the antibacterial effect.With the result of that,it will improve the structure of the intestinal flora,promote the growth of beneficial microorganisms in the intestine,and inhibit the reproduction of pathogenic bacteria,which can exert its preventive and protective effect on the challenged broilers.According to the results of this study,the concentration of 200 mg/kg gallic acid was the better one. |
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