Effects Of Antimicrobial Peptides On Growth Performance,Nutrient Availability Andintestinal Development Of Broilers

At present,the era of "total ban of resistance in feed" has come.It is necessary to seek safe,green and residue free substitutes for feeding antibiotics in order to ensure the healthy and sustainable development of animal husbandry.As a kind of green feed additive without pollution,residue and harm to the body,antimicrobial peptides play an important role in promoting the healthy growth of the body,optimizing the ecological environment and strengthening food safety.In this study,the effects of antimicrobial peptides on growth performance,nutrient availability,immune organ index,intestinal p H value,intestinal SIg A expression level and intestinal tissue structure of broilers were investigated by adding antimicrobial peptides into the diet.The immune protection effect of antimicrobial peptides on broiler chickens was investigated by Salmonella challenge test,which provided theoretical basis and practical guidance for the application of antimicrobial peptides in broiler production.Test using single factor experiment design,select 1 day age Yi Ba increasingly(AA)600broilers,were randomly divided into 4 process,namely the control group,antibiotics group,300 mg/kg of antimicrobial peptide group and 500 mg/kg of antimicrobial peptides,respectively fed without antibiotic based diet of corn,soybean meal and add in the basic diet of 200 mg/kg,doxycycline,300 mg/kg of antimicrobial peptides and 500 mg/kg of antibacterial peptide of fodder.Each treatment had 6 replicates(half male and half female)with 25 chickens per replicate.The experiment lasted for 42 days and was divided into two stages: early stage(d 0-21)and later stage(d 21-42).On the 18 th and 39 th day of the experiment,four replicates were selected from each treatment,and four healthy broilers with similar weight were randomly selected from each replicate for a 3-day metabolic test to investigate the effects of antimicrobial peptides on nutrient apparent digestibility of broilers.After the metabolic test,6 broilers(1 chicken per replicate)were selected from each treatment and slaughtered.Blood,intestinal tissue and colon chyme samples were collected,and the thymus,spleen and bursa of Fabricius were weighed.In addition,on the 42 nd day of the experiment,8 broilers were selected from each treatment to be challenged with Salmonella pullosum,and the changes of various indexes were observed after the challenge.The results showed as follows: compared with the control group,(1)dietary supplemented with 300mg/kg or 500mg/kg antimicrobial peptide significantly increased the final weight and average daily gain of broilers d 22-42 and d 1-42(P < 0.05),significantly decreased the ratio of feed to gain(P < 0.05);(2)Adding 300mg/kg antimicrobial peptides significantly increased the serum total protein level of broilers at the 21 st day(P < 0.01),significantly decreased the serum triglyceride and cholesterol levels of broilers at the 21 st day and the serum triglyceride levels at 42d(P < 0.05);The supplementation of 500mg/kg antimicrobial peptide significantly increased the serum total protein and albumin levels of broilers at the 21 st day and the serum total protein levels at the 42 nd day(P < 0.05),significantly decreased the serum triglyceride and cholesterol levels at the 21 st day and the serum triglyceride levels at the 42 nd day(P < 0.05);(3)Dietary supplementation of 300mg/kg significantly increased the apparent metabolic rate of crude protein and ether extract of broilers d 22-42(P < 0.05),and had a tendency to increase the apparent metabolic rates of crude protein and ether extract of broilers D 19-21(0.05 ≤ P < 0.1);(4)Adding 300mg/kg of antimicrobial peptide significantly increased thymus index of broilers at the 21 st day(P <0.01)and bursa of Fabricius index on the 42 nd day(P < 0.05),and the supplementation of500mg/kg antimicrobial peptide significantly increased the spleen index of broilers on the21 st day(P < 0.05)and spleen index on the 42 nd day(P < 0.01),had a tendency to increase thymus index of broilers at 42 days of age(0.05 ≤ P < 0.1);(5)Adding 300mg/kg or500mg/kg of antimicrobial peptides significantly increased duodenal and jejunal velocipidity ratio of broilers at the 21 st day(P < 0.01)and on the 42 nd day,the villus height of different segments of small intestine,the velocious-secrete ratio of jejunum and ileum(P < 0.01),the crypt depth of small intestine and ileum on the 21 st day and the 42 nd day was significantly decreased(P < 0.01);(6)Adding 300mg/kg antimicrobial peptides significantly increased the abundance of lactic acid bacteria in broilers on the 42 nd day(P < 0.01),adding 500mg/kg antimicrobial peptide significantly increased the abundance of lactic acid bacteria in cecum of broilers at the 21 st and 42 d days(P < 0.05);(7)After challenge treatment,adding 300mg/kg or500mg/kg antimicrobial peptides tended to increase the average daily gain and decrease the ratio of feed to gain of broilers(0.05 ≤ P < 0.1),and alleviate the intestinal,liver and spleen lesions caused by Salmonella infection,and improve fecal morphology;In addition,adding300mg/kg antimicrobial peptides significantly increased the content of lactic acid bacteria in cecum of broilers(P < 0.01),had a tendency to increase the content of Escherichia coli(0.05≤ P < 0.1).In conclusion,the supplementation of 300mg/kg or 500mg/kg antimicrobial peptides can improve the growth performance,nutrient apparent metabolic rate and immune performance,improve the intestinal morphological development and intestinal flora composition of broilers,and alleviate the organ damage caused by Salmonella pullorum infection in broilers.In general,the effect was better when the supplemental amount was 500mg/kg.