| At the later stage of laying,the immune ability,production performance and egg quality of laying hens decreased,which affected the economic benefits of breeding.Antimicrobial peptides have the advantages of broad-spectrum antibacterial,immune regulation,stable biological activity and not easy to produce drug resistance.In this experiment,the antibacterial effect and stability of antimicrobial peptides were first studied in vitro,and then,the effects of the compound on the production performance,egg quality,antioxidant function,immune function and intestinal health of laying hens were studied,and the appropriate supplemental level of compound was determined to provide technical reference for its rational application in diet of laying hens.1: Study on antibacterial activity and stability of antibacterial peptides in vitro.In this experiment,Escherichia coli,Salmonella and Staphylococcus aureus were used to detect the antibacterial activity and minimum inhibitory concentration(MIC)of antimicrobial peptides in vitro.Taking Escherichia coli as an example,the bacterial growth curve was detected,and the effects of different temperatures,proteases and p H on the antibacterial activity of antimicrobial peptides were detected.The results showed that the MIC of the three strains were all 4 μg /m L.The antibacterial effect of antimicrobial peptides was proportional to the content of antimicrobial peptides.Temperature and trypsin had no effect on the MIC of antimicrobial peptides.When pepsin and p H value were 2,the MIC of antimicrobial peptides to EScherichia coli and Staphylococcus aureus increased to 8 μg/m L,while when p H value was 4～10,the MIC of antimicrobial peptides to the three test bacteria remained unchanged.2: Effects of antimicrobial peptides on production performance,egg quality and nutrient utilization of laying hens.120 Hailan Brown laying hens of 66 weeks old with similar weight and laying rate were randomly divided into 4 groups,with 6repetitions in each group and 5 laying hens in each repetition.The control group was fed with basic diet,and the experimental group was fed with antibacterial peptides of100 mg/kg,200 mg/kg and 400 mg/kg respectively.The pre-test period was 7 days and the pilot period was 56 days.The results showed that 100 mg/kg and 200 mg/kg antibacterial peptide groups could significantly improve the laying rate of laying hens(P<0.05),and 200 mg/kg antibacterial peptide group could significantly reduce the feed egg ratio and increase the average egg weight(P<0.05).At the end of the 4th week,400 mg/kg antibacterial peptide group could significantly increase the protein height and huff unit of laying hens(P<0.05);At the end of 8 weeks,100 mg/kg antibacterial peptide group could significantly increase the proportion of egg yolk(P<0.05),200 mg/kg antibacterial peptide group could significantly improve the strength of egg shell(P<0.05),200 mg/kg and 400 mg/kg antibacterial peptide groups could significantly improve the thickness and color of egg shell(P<0.05).Antimicrobial peptides had no significant effect on the utilization of dry matter,organic matter,crude protein and crude fat in laying hens at the later stage of laying(P>0.05),but 200 mg/kg antimicrobial peptides could significantly improve the utilization of crude ash(P<0.05).3: Effects of antimicrobial peptides on serum biochemical indexes and antioxidation of laying hens.Sserum was collected and sparated on the 28 th and 56 th days of the experiment.The results showed that on the 28 th day of the experiment,serum GLO content in experimental groups was significantly increased(P<0.05),TP and P contents and AKP activity in 400 mg/kg antimicrobial peptide group were significantly increased(P<0.05);On the 56 th day of the experiment,experimental groups could significantly increase GLO and P contents and decrease TC content(P<0.05),200 mg/kg antibacterial peptide group could significantly increase the activity of AKP(P<0.05),and 400 mg/kg antibacterial peptide group could significantly increase the content of TP(P<0.05).On the 28 th day of the experiment,the T-SOD and GSH-Px activities of test groups were significantly increased(P<0.05),and the contents of T-AOC in 200 mg/kg and 400 mg/kg antimicrobial peptide groups were significantly increased(P<0.05);On the 56 th day of the experiment,T-AOC content and GSH-Px activity in all test groups were significantly increased(P<0.05),while MDA content was decreased(P<0.05).T-sod activity was significantly increased in 200 mg/kg and 400 mg/kg antimicrobial peptide groups(P<0.05).4: Effect of antimicrobial peptides on immune function of laying hens.The results showed that on the 28 th day of the experiment,all test groups could significantly increase the content of Ig A in laying hens’ serum(P<0.05),100 mg/kg antibacterial peptide group could significantly increase the content of IL-2(P<0.05),200 mg/kg antimicrobial peptide group significantly increased IL-10 content(P<0.05),and 200 mg/kg and 400 mg/kg antibacterial peptide groups could significantly increase the content of Ig G and IFN-γ(P<0.05);On the 56 th day of the experiment,each experimental group could significantly increase the contents of Ig M and IFN-γ(P<0.05),and the 200 mg/kg and 400 mg/kg antimicrobial peptide groups could significantly increase the contents of Ig A,Ig G,IL-4 and IL-10.(P<0.05),the 200mg/kg antimicrobial peptide group could significantly increase the content of IL-2 and TNF-α(P<0.05).The 400 mg/kg antimicrobial peptide group could significantly increase the level of Newcastle disease antibody titers after 14 days of immunization and avian influenza antibody titers after 42 days of immunization(P<0.05).On the28 th day of the experiment,the 200 mg/kg and 400 mg/kg antimicrobial peptide groups could significantly increase the transformation rate of T lymphocytes(P<0.05);on the 56 th day of the experiment,each experimental group could significantly increase the transformation rate of T lymphocytes(P<0.05).5: Effects of antimicrobial peptides on intestinal health of laying hens.At the end of the trial period,the contents of small intestine,its mucosa and cecum were collected for analysis and determination.The results showed that each test group could significantly increase the content of s Ig A in the duodenal mucosa(P<0.05),and the 200 mg/kg and 400 mg/kg antimicrobial peptide groups could significantly increase the content of s Ig A in the ileal mucosa(P<0.05).All test groups could significantly increase the activities of jejunal lipase,trypsin and ileal trypsin(P<0.05).The 200 mg/kg antimicrobial peptide group could significantly increase the jejunal α-amylase activity(P<0.05).The 400 mg/kg antimicrobial peptide group could significantly increase the activities of duodenal α-amylase,lipase and ileal α-amylase(P<0.05).Jejunum crypt depth was significantly decreased in 100 mg/kg and 200mg/kg antimicrobial peptide groups(P<0.05),and the 200 mg/kg antimicrobial peptide group could significantly reduce the duodenal crypt depth and increase the jejunal crypt 200 mg/kg and 400 mg/kg antimicrobial peptide groups could significantly increase the height of duodenal villi,reduce the depth of ileal crypts,and increase the ratio of chorionic crypts between duodenum and ileum(P<0.05).The100 mg/kg antimicrobial peptide group could significantly increase the abundance expression of Firmicutes,Ruminococcus,and Bacteroidetes(P<0.05),and the 200mg/kg antimicrobial peptide group could significantly increase the abundance of Bacteroidetes,Syntrophobacteria,Rumenococcus,Bacteroidetes,Rikenbacteriaceae RC9 intestinal group abundance expression(P<0.05),400 mg/kg antimicrobial peptide group can significantly increase Bacteroidetes,Syntrophobacteria,Rikenbacteriaceae RC9 intestinal group abundance expression of tract groups(P<0.05).In summary,antimicrobial peptides could improve the immune function,antioxidant capacity and intestinal health of laying hens in the later stage of laying,so as to improve the production performance and egg quality of laying hens in the later stage of laying.After comprehensive analysis of various indicators,it was preliminarily concluded that the optimal supplemental level of antimicrobial peptides was 200 mg/kg. |
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