Effect Of Chitooligosaccharide On Growth Performance,Intestinal Immunity,Barrier Function And Meat Quality In Broilers

Antibiotics have excellent therapeutic effectiveness and growth promotion properties and have been used as feed additives for livestock for several decades.However,their usage has caused potential adverse effects.The China starts to ban antibiotics used in feed comprehensively in 2020.It is therefore urgent to develop and utilize the safe and non-residue feed additives.The chitooligosaccharide(COS),as a functional prebiotic,has many excellent biological functions.The aim of present study was to investigate the effects of dietary COS supplementation as an alternative to antibiotics on growth performance,intestinal immune fuction,antioxidant capacity,barrier function,mineral deposit and meat quality.The experiment is divided into the following three parts:Experiment 1:Effect of COS on growth performance and immune fuction in broilers.In total,144 one-day-old Arbor Acres broiler chicks were used in this experiment,and they were assigned to one of the three treatments consisting of 6 replicates with eight broilers each.The chicks in three treatments were fed a basal diet free from antibiotics(Control group)and the same diet supplemented with either 50 mg/kg of chlortetracycline(Chlortetracycline group)or 30 mg/kg of COS(COS group)for 42 days(d).Compared with the control group,dietary supplementation with COS reduced feed to gain ratio(1-21 d,22-42 d and 1-42 d),and malondialdehyde levels in jejunum,ileum at 21 d as well as duodenum and ileum at 42 d(P<0.05),whereas enhanced the immunoglobulin G(IgG)and immunoglobulin M(IgM)levels of duodenum and jejunum,and duodenal superoxide dismutase(SOD)acitivity in broilers at 21 d(P<0.05).Compared with the chlortetracycline group,supplementation with COS increased duodenal IgM concentration and SOD activity in broilers at 21 d(P<0.05).In addition,the feed to gain ratio(1-21 d,1-42 d),malondialdehyde(MDA)contents of duodenum and ileum in broilers at 42 d in chlortetracycline group were observed to be lower in comparison with control group(P<0.05),whereas the jejunal IgM and IgG levels of duodenum,jejunum and ileum in broilers at 21 d were higher than those in control group(P<0.05).Experiment 2:Effect of COS on intestinal barrier function and cecal microbial structure in broilers.The experiment design and materials were the same as those in experiment 1.Compared with the control group,the COS group increased duodenal villus height at 21 d(P<0.05),villus height to crypt depth ratio of duodenum and jejunum at both 21 and 42 d(P<0.05),and upregulated the duodenal and jejunal claudin 3(CLDN3)mRNA expression in broilers at 21 d(P<0.05),whereas reduced crypt depth of jejunum,serum diamine oxidase activity and endotoxin content at 21 d,and crypt depth of duodenum and ileum at 42 d(P<0.05).Compared with chlortetracycline group,inclusion of COS increased jejunal villus height to crypt depth ratio at 42 d(P<0.05),ileum crypt depth,and upregulated CLDN3 mRNA expression in duodenum and jejunum at 21 d(P<0.05).However,the alpha and beta diversity in cecum microbiome did not differ among groups(P>0.05).Experiment 3:Effect of COS on mineral deposit,meat antioxidant capacity and quality in broilers.The in vitro experiment aimed to investigate the metal element absorption of COS by simulating gizzard,crop and small intestine pH value in broilers.The animal experiment design and materials were the same as those in experiment 1.As in vitro results shown,COS decreased the Fe content when pH value was 5 or 6(P<0.05)and Zn concentration when pH value was 2.5 or 6(P<0.05),whereas increased Fe content when pH value was 2.5(P<0.05).Furthermore,the Cd content was observed to be lower in response to COS treatment for 70 min with the pH value being 2.5(P<0.05).Compared with the control group,dietary COS inclusion reduced serum Cu,breast meat Cd and MDA content,cooking loss,24 h and 48 h drip loss(P<0.05)in broilers at 42 d,whereas enhanced 24-h pH value postmortem(P<0.05),with the values of these parameters being similar between COS group and chlortetracycline group(P>0.05).It can be concluded as follows:(1)Dietary supplementation with 30 mg of COS per kg of diet could improve feed conversion ratio,intestinal immunity and barrier function in broilers,with theses positive effects being more obvious for the broilers at an early age(1-21 d).(2)Inclusion of COS could reduce serum Cu and breast meat Cd content,whereas improve meat quality and antioxidant capacity in broilers.(3)Dietary COS inclusion had the same or even better effects as those observed after dietary chlortetracycline inclusion,implicating that dietary COS supplementation can be used as a potential alternative to antibiotics in broilers.