| ?- Defensin and Cathelicidins are two main antimicrobial peptides families in poultry, and play an important role in innate immunity against infection. Lactobacillus rhamnosus(L.rhamnosus) MLGA and its cell wall peptidoglycan can promote the expression of avian ?-defensing 9(Av BD9) gene in immune cells and chicken intestine. However, the mechanisms of action by L.rhamnosus MLGA to protect broiler against infection and the regulatory mechanism underlying the defensin gene expression by nutrients remain unclear. In this study, the growth performance, immunoglobulin and cytokine contents in serum, and intestinal mucosa s Ig A were measured to determine the appropriate dosage of L. rhamnosus MLGA in broiler diets. Moreover, the effects of administration of L. rhamnosus MLGA on innate immunity of broilers challenged with Salmonella enteritidis(S. enteritidis) were investigated to plemiminarily explore the mechanism of action of L. rhamnosus against infection, thus contributing to the screening, modification of probiotics with higher efficacy and then their application and popularization.Trial 1: A total of 200 AA male broiler chickens were randomly allotted to 5 groups and with 4 replicates of 10 broilers each.Each group was fed the antibiotic-free basal diet supplemented with 0(control), bacitracin zinc 40mg/kg,1×109,1×1010 or 1×1011 cfu/kg L. rhamnosus MLGA to 21 days of age respectively. On d 14 and 21, average daily feed intake(ADFI), average daily gain(ADG) and feed to gain ratio(F/G) were calculated. Two birds were randomly selected from each replicate on d 21 and 42, blood samples were collected from the wing vein, and then killed by bleeding. Bursa of fabricius, thymus, spleen, cecal contents and jejunum mucous membrane were immediately collected. The cytokines and immunoglobulins in serum, s Ig A in mucousa, immune organ index and bacteria carrying amount of E. coli in cecal contents were determined. The results showed that dietary supplementation of L. rhamnosus MLGA at 1 × 109cfu/kg, 1 × 1010cfu/kg and 1 × 1011cfu/kg significantly reduced feed to gain ratio and improved growth performance of broilers aged from 1 to 21 days(P<0.05). Administration of L. rhamnosus MLGA tended to increase serum immunoglobulins and intestinal mucosa s Ig A in broilers.Addition of 1 × 1010cfu/kg L. rhamnosus MLGA significantly increased t IL-10 and reduced IL-6 contents in serum(P<0.05). Both levels of 1 × 1010 cfu / kg and 1 × 1011 cfu / kg L. rhamnosus MLGA significantly inhibited the proliferation of Escherichia coli in cecum(P<0.05). Based on the results, the appropriate supplemental level of L. rhamnosus MLGA at 1 x 1010cfu/kg in the broiler diets is recommended.Trial 2: A total of 120 AA male broiler chickens were randomly allotted to 3 groups and with 4 replicates of 10 broilers each. The three treatment groups were control group, Salmonella enteritidis-infected group and Salmonella enteritidis-infected group fed with Lactobacillus rhamnosus MLGA at 1×1010cfu/kg. One broiler was randomly selected from each replicate on d 7,10,14 and 21, blood samples were collected from heart. Liver, cecal contents, about 3cm of the middle of duodenum, ileum and jejunum were immediately collected. The cytokines in serum, villus length, crypt depth of broilers, bacteria carrying amount of S. enteritidis in cecal contents and liver were determined. The results showed that continuous administration of L. rhamnosus MLGA at 1 × 1010cfu/kg reduced serum C-reactive protein(CRP), RANTES, IL-8 and TNF-?, and improved TGF-?1 contents of broilers challenged with S. enteritidis(P<0.05). Dietary supplementation of L. rhamnosus MLGA significantly reduced S. enteritidis numbers in cecal contents(P<0.01). L. rhamnosus MLGA improved jejunum villi length and increased villus height to crypt depth ratio in S. enteritidis challenged broilers.Trial 3: The groups and diets were as same as Experiment II. One broiler was randomly selected from each replicate on d 7,10,14 and 21, blood samples were collected from heart. and then killed by bleeding.Bursa of fabricius, thymus, spleen, liver, jejunum, ileum and cecum were immediately collected on ice bath. The innate immunity-associated gene expressions were determined. The results showed that Continuous administration of L. rhamnosus MLGA at 1 × 1010cfu/kg upregulated m RNA expressions of innate immunity associated-genes of TLR2, Cath-B1 and Av BD9 at varying degrees in tissues and PBMC in broilers challenged with S. enteritidis, indicating L. rhamnosus MLGA can improve immune function of broiler chickens against S. enteritidis infection.In conclusion, dietary supplementation Lactobacillus rhamnosus MLGA can significantly improve the production performance of broilers. And it can significantly inhibited the proliferation of Escherichia coli in the cecum. The broilers infected with Salmonella enteritidis before and after continuous feed Lactobacillus rhamnosus MLGA could regulating the secretion of cytokines, inhibits the proliferation of Salmonella, increased expression of defensins to improve the body's ability to resist infection by intestinal pathogens. |
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