Effects Of Selenium-enriched Exopolysaccharide Poduced By Enterobacter Cloacae Z0206on Growth Performance And Immune Function In Animals

Enterobacter cloacae Z0206(E. cloacae Z0206), a recent discovered bacterial strain, could produce huge amount of exopolysaccharides. Our previous studies found that E. cloacae Z0206could accumulate selenium (Se) in the form of Se-enriched exopolysaccharide (Se-ECZ-EPS) efficiently in medium enriched with selenium. Se-ECZ-EPS contained535.7mg/kg Se. Se-ECZ-EPS has been shown to improve the innate, cellular and humoral immune responses in immunosuppressed mice induced by cyclophosphamide and protect RAW264.7cells from oxidative damage and apoptosis induced by H2O2.However, little was known about the bioactive activities of Se-ECZ-EPS in crayfish, broilers and weaning piglets. Thus the present study was conducted to investigate the effects of Se-ECZ-EPS on growth performance, antioxidant status, immune function, intestinal morphology and intestinal microbial diversity in crayfish, broilers and weaning piglets. To develop Se-ECZ-EPS into a potential immunomodulator in animals, the acute toxicity of Se-ECZ-EPS in rat was investigated. The researches provide the basis for the application of Se-ECZ-EPS in husbandry.Exp.l. Study on the acute toxicity of Se-ECZ-EPS in rat.To develop Se-ECZ-EPS into a potential immunomodulator in animals such as crayfish, broilers and weaning piglets, this study was conducted to investigate the acute toxicity of Se-ECZ-EPS in rat according to GB15193.4-2003. The acute oral maximum-tolerated dose (MTD) of Se-ECZ-EPS were greater than20.0g/kg in male and female rats, and Se-ECZ-EPS was classified as non-toxic substance. This study provide the basis for the application of Se-ECZ-EPS in husbandry.Exp.2. Effects of Se-ECZ-EPS on immune function in crayfish.To investigate the modulation of immunity in crustaceans, we examined phenoloxidase (PO) activity, respiratory burst (RB) ability, superoxide dismutase (SOD) level and several immune-related gene expression profile in red swamp crayfish [Procambarus clarkii (Girard)] that were individually induced with Se-ECZ-EPS at1μg g-1.The protection of crayfish against the white spot syndrome virus (WSSV) by Se-ECZ-EPSwas also investigated.The results showed that PO, RB and SOD activities of crayfish increased significantly (P<0.05) at24,48and72h after being injected with Se-ECZEPS. Among the genes examined, the mRNA expressions of serine proteinase, HSP70and Mn-SOD were significantly up-regulated at24and48h after the Se-ECZ-EPS treatment, while no significant changes in the expression in proPO were observed from24to72h. The survival rate of crayfish that received Se-ECZ-EPS was significantly higher than that of the control group after14days (59.7%and0%respectively). Taken together, it can be concluded that Se-ECZ-EPS is an efficient immunostimulant and can improve the immunity of crayfish.Exp.3. Effects of Se-ECZ-EPS on growth performance, immune function and intestinal morphology in broilers.3.1Effects of Se-ECZ-EPS on growth performance and carcass quality in broilers.This study was conducted to investigate the effects of Se-ECZ-EPS on growth performance and carcass quality in broilers. Two hundred and forty Avian broiler chickens were allocated randomly into five groups with four replicates in each group and twelve chickens in each replicate. Control group was fed with basal diet containing0.15mg/kg Se (Na2SeO3), and the another four groups were fed with diets supplemented with Se-ECZ-EPS at the level of280mg/kg (0.15mg/kg Se),560mg/kg (0.30mg/kg Se),840mg/kg (0.45mg/kg Se) and1120mg/kg (0.60mg/kg Se), respectively. The results showed that average daily gain and feed conversion ratio in840and1120mg/kg groups were significantly enhanced from0to42days compared to the control group (P<0.05). Drip loss of muscles in chest and leg were significantly decreased in560、840and1120mg/kg groups(P<0.05).These results implicated that Se-ECZ-EPS can decrease drip loss of muscles and improve the growth performance in broilers.3.2Effects of Se-ECZ-EPS on immune function in broilers.This study was conducted to investigate the effects of Se-ECZ-EPS on immune function in broilers. Administration of Se-ECZ-EPS at the level of560,840and1120mg/kg significantly increased activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and decreased malondialdehyde (MDA) production compared with the control and280mg/kg group(P<0.05). Compared with the control, the serum concentrations of TNF-a and IL-2showed positive responses in broilers fed with Se-ECZ-EPS at the levels of280、560、840and1120mg/kg (P<0.05). Significant increases in the level of IL-6were observed only in the serum of birds treated with Se-ECZ-EPS at560and1,120mg/kg as compared with the control group (P<0.05). At21days and35days of age, the HI titers against NDV in groups supplied with Se-ECZ-EPS at840and1,120mg/kg were significantly higher than that in the control (P<0.05) At42days of age, a significant increase in HI titer was observed only in birds treated with Se-ECZ-EPS at840mg/kg as compared with the normal control (P<0.05) And1120mg/kg group significantly improve avian influenza antibody levels in7d and14d after immunization (P<0.05). These results implicated that Se-ECZ-EPS can improve the growth performance through enhancing immune functions in broilers.3.3Effects of Se-ECZ-EPS on intestinal morphology in broilers.This study was conducted to investigate the effects of Se-ECZ-EPS on intestinal morphology in broilers. Duodenum crypt depth was shallow and villus height and crypt depth ratio (VCR) was significantly high in560and840mg/kg groups (P <0.05). And jejunum villous height in1120mg/kg group was significantly increased (P<0.05).These results implicated that Se-ECZ-EPS can improve the growth performance through enhancing intestinal absorption function in broilers. Exp.4. Effects of Se-ECZ-EPS on growth performance, immune function, intestinal morphology and intestinal microbial diversity in weaning piglets.4.1Effects of Se-ECZ-EPS on growth performance in weaning piglets.This study was conducted to investigate the effects of Se-ECZ-EPS on growth performance in weaning piglets. A total of150piglets [(Landrace×Yorkshire)×Duroc] weaned at28d of age with an initial BW of8.11±0.12kg were randomly allocated into5groups of3replicates each. The5treatments were: basal control diet (CON), Na2SeO3diet (CON+0.30mg/kg Na2Se03), Na2SeO3+astragalus polysaccharide (APS) diet (CON+0.30mg/kg Na2SeO3+560mg/kg APS), Na2SeO3+EPS diet (CON+0.30mg/kg Na2SeO3+560mg/kg EPS) and Se-ECZ-EPS diet (CON+560mg/kg Se-ECZ-EPS). Compared with CON group, ADG was significantly enhanced in the Na2Se03+APS, Na2Se03+EPS and Se-ECZ-EPS groups and F:G was significantly decreased(P<0.05). There were no differences in ADG and F:G between pigs fed the Na2SeO3+APS, Na2Se03+EPS and Se-ECZ-EPS diets. These results implicated that Se-ECZ-EPS can improve the growth performance in weaning piglets.4.2. Effects of Se-ECZ-EPS on immune function in weaning piglets.This study was conducted to investigate the effects of Se-ECZ-EPS on immune function in weaning piglets. The Na2SeO3+EPS and Se-ECZ-EPS groups had higher serum T-AOC and lower MDA than the CON group (P<0.05). GSH-Px and SOD activities in Se-ECZ-EPS group were significantly increased compared with CON group (P<0.05). There were no differences in T-AOC、GSH-Px、SOD and MDA between pigs fed the Na2SeO3+APS, Na2Se03+EPS and Se-ECZ-EPS diets. Increases in serum TNF-a, IL-2and IL-6were observed in the Na2SeO3+EPS and Se-ECZ-EPS groups compared with the CON (P<0.05), and there were no difference in the TNF-a, IL-2and IL-6levels between pigs fed Na2SeO3+APS, Na2SeO3+EPS and Se-ECZ-EPS diets. The Se-ECZ-EPS group had higher serum IgG than the CON and Na2SeO3groups (P<0.05), and higher serum IgM than the CON, Na2Se03and Na2Se03+APS groups (P<0.05). Pigs fed with Na2Se03+APS, Na2SeO3+EPS and Se-ECZ-EPS diets had higher PR-39and Hepcidin gene expression levels in liver (P <0.05). The Se-ECZ-EPS group had higher pBD-1gene expression in duodenum and pBD-2gene expression in jejunum and ileum compared with the CON group (P <0.05). The Na2Se03+EPS group had higher pBD-2gene expression in jejunum and ileum, and the Na2SeO3+APS group had higher pBD-2gene expression in ileum compared with the CON group (P<0.05). These results implicated that Se-ECZ-EPS can improve the growth performance through enhancing immune functions in weaning piglets.4.3Effects of Se-ECZ-EPS on intestinal morphology and intestinal microbial diversity in weaning piglets.This study was conducted to investigate the effects of Se-ECZ-EPS on intestinal morphology and intestinal microbial diversity in weaning piglets. Villous height in jejunum and villus height and crypt depth ratio (VCR) in duodenum and jejunum were significantly increased in Na2Se03+EPS and Se-ECZ-EPS groups (P<0.05). Gut microbial diversity display that Se-ECZ-EPS can increase microbial diversity index (Shannon index) in colon and cecum. Compared with Na2SeO3group, Se-ECZ-EPS can increase Gram-positive bacteria (Firmicutes) and decrease gram-negative bacteria (Bacteroides door) in colon and cecum. These results implicated that Se-ECZ-EPS can improve the growth performance through regulating the balance of intestinal flora in weaning piglets.