Effects Of Dietary Apidaecin Api-PR19 On Growth Performance,Intestinal Health And Microbiota In Broilers

In the past few decades,sub-therapeutic dose of antibiotics have been commonly used as feed additives in poultry industry to prevent disease and promote livestock growth.However,excessive use of antibiotic growth promoters(AGPs)in poultry farming can lead to negative effects such as gut microbiota imbalance,evolution and selection of drug-resistant bacteria,and drug residue.Therefore,many countries have gradually banned the addition of antibiotic growth promoters in poultry feed.China ’s Ministry of Agriculture and R ural Affairs Document No.194 Announcement : China has completely banned the use of antibiotics as a dietary additive in 2020.In order to meet the growing demand for antibiotic growth promoters substitutes in the poultry industry,many new green feed additives have been developed to maintain intestinal health and promote growth performance of broilers.This experiment was conducted to investigate the effects of dietary Api-PR19 on growth performance,nutrient digestibility,intestinal morphology,expression of intestinal nutrient transporters and tight-junction protein-related genes and intestinal flora of broilers,in order to reveal the effects of Api-PR19 on growth performance,intestinal health and intestinal flora of broilers.Exp.1 Effects of dietary supplemented with Api-PR19 on Growth Performance of BroilersThis experiment investigated the effects of antimicrobial peptide Api-PR19 as a feed additive on growth performance of Arbor Acres(AA)white feathered broilers.A total of 360 one-day-old AA white feathered broilers were randomly divided into three groups as follows: 1)control group(CON): fed with basal diet;2)Antibiotic group(AGP): basal diet and 10 mg/ kg colistin sulfate and 50 mg/ kg roxarsone;3)Antimicrobial peptide group(ABP): basal diet and 330 mg/ kg antimicrobial peptide Api-PR19.There were 6 replicates in each group and 20 AA broilers per replicate.The trial lasted for 35 days.The results showed as follows:compared with the control group,dietary Api-PR19 significantly increased the average daily feed intake(P < 0.05)and average daily gain(P < 0.05)of broilers in the early feeding period(1-21 days of age),and significantly decreased the feed conversion rate(P < 0.05),but had no significant effect on the performanc e of broilers in the late feeding period(22-35 days of age)and the whole period(1-35 days of age).Exp.2 Effects of dietary supplemented with Api-PR19 on intestinal health of broilersIn this experiment,intestinal mucosa and chyme samples of each inte stinal segment(duodenum,jejunum and ileum)of broilers at 35 days of age were collected.Intestinal morphology was detected;Nutrient digestibility and intestinal digestive enzyme activities of broilers were determined.The m RNA expression levels of glucose transporters(SGLT1,GLUT2),amino acid transporters(r BAT,B0 AT,EAAT3),fatty acid transporters(FATP4)and tight junction proteins(ZO-1,Claudin-1)in intestinal tract and secreted immunoglobulin(s I g A)expression in duodenum,jejunum and ileum were determined.The results showed as follows: 1)the dry matter digestibility and crude protein digestibility of AGP and ABP groups were significantly higher than those of control group(P < 0.05),the duodenal trypsin activity of ABP group was significantl y higher than that of control group(P< 0.05),but the duodenal lipase and amylase activities of AGP and ABP groups were not significantly different from that of control group.2)Compared with control group,villus height/crypt depth in duodenum and jeju num of 35-day-old AA white feathered broilers in AGP and ABP groups was significantly increased(P< 0.05).3)In addition,compared with the control group,dietary Api-PR19 significantly increased the gene expressions of amino acid transporter 3(EAAT3),glucose transporter(GLUT2)and tight ligin(ZO-1,Claudin-1)in duodenum of broilers at 35 days of age(P < 0.05).4)Immunohistochemical results showed that Api-PR19 significantly increased duodenal sIgA content(P < 0.05).Exp.3 Effects of dietary sup plemented with Api-PR19 on small intestinal microflora of BroilersThis experiment sequenced the 16 S r RNA gene in the small intestine contents(mixed contents of duodenum,jejunum and ileum)of broilers.The results showed as follows: dietary Api-pr19 significantly decreased α diversity of small intestinal flora(P < 0.05).β diversity showed that the addition of bee antimicrobial peptide Api-pr19 significantly changed the intestinal flora structure of broilers(P < 0.05).At the phylum level,Firmicutes(8 8.36%)and Bacteroidota(6.13%)were the dominant bacterial groups in the intestinal flora of broilers at 35 days of age.On the genus level,the top 3 genera in CON group were Lactobacillus(63.62 %),Bacteroides(5.74 %)and Staphylococcus(2.54 %),respectively.ABP group were respectively Lactobacillus(70.64 %),Enterococcus(6.67 %)and Brochothrix(4.00 %).The LEf Se analysis showed that g＿Clostridium＿sensu＿stricto＿1,g＿Candidatus＿Arthromitus,g＿Romboutsia,g＿blautia,g＿Caproiciproducens,g＿Subdoligranulum were higher in CON group.p＿Firmicutes,g＿enterococcus,g＿Carnobacterium,g＿Kitasatospora,g＿Acidaminococcus were dominant in ABP group.RDA analysis showed that ABP mediated intestinal flora,especially Enterococcus,was positively correlated with growth performance,intestinal morphology and intestinal sIgA content.In conclusion,dietary apidaecin Api-PR19 supplementation could improve growth performance of broilers by modulating intestinal microbiota which promoted intestinal development,nutrients absorption and immune function.