| With the intensive aquatic animal farming,the imbalance of nutrient ratio and environmental pollution in feeds have attracted more and more attention,posing a serious threat to the intestinal health and immunity of aquatic animals,thus affecting their growth and development.The development of polysaccharides as green feed additives has become a hot research topic.In this experiment,Channa argus were subjected to different levels of Lycium barbarum polysaccharides(LBP)in feed,which were divided into control group(0 mg/kg),LBP1(500 mg/kg),LBP2(1000mg/kg),LBP3(1500 mg/kg),LBP4(2000 mg/kg),and LBP5(2500 mg/kg)were fed for 8 weeks.By changing the concentration of LBP in the feed,the effects on growth performance,feed utilization,intestinal barrier function and immune function of Channa argus were investigated.The study of this thesis was divided into three parts,and the main findings and conclusions of the study were as follows:(1)Effect of LBP in feed on growth performance and feed utilization of Channa argus.In order to study the effect of LBP in feed on the growth performance and feed utilization of Channa argus,the growth performance,body shape index,feed utilization and muscle nutrient composition analysis of Channa argus were measured after 56 d of feeding.The results showed that the mean weight gain rate of Channa argus was significantly higher in the LBP3 group than in the LBP1,LBP2,LBP5 groups(P<0.05),while there was no significant difference in the LBP2,LBP4 groups(P>0.05).The specific growth rate of Channa argus was significantly increased in all the groups with LBP added to the feed(P<0.05),and the specific growth rate was highest in the LBP3 group,which was not significantly different from the LBP2,LBP4 groups(P>0.05).Compared with the control group,both feed efficiency and protein efficiency were improved in the LBP addition group,and the LBP3,LBP4 groups were significantly higher than the other groups(P<0.05).The dirty body ratio in the LBP group was significantly lower than that in the control group(P<0.05).There was no significant difference in fatness and liver to body ratio among the test groups(P>0.05).There was no significant difference in moisture and crude ash content of muscle in each group(P>0.05).Muscle crude protein content was significantly higher in LBP3,LBP4 groups(P<0.05).According to the parabolic regression analysis of feed LBP addition levels with mean weight gain rate and protein efficiency,respectively,the optimum addition levels of LBP in feed were 1474.68～1587.05 mg/kg.(2)Effect of LBP in feed on intestinal barrier function of Channa argus.In order to study the effect of LBP in feed on the intestinal barrier function of Channa argus,the intestinal tissues of each group were taken after 56 d of feeding to Channa argus,and the related indexes such as intestinal flora,digestive enzymes,antioxidant enzymes and immunity were examined.Illumina Mi Seq sequencing results showed that the addition of LBP in feed reduced the proportion of Proteobacteria in the intestinal flora of Channa argus.Alpha diversity analysis of the intestinal flora richness index was significantly higher in the LBP3 group(P<0.05),and the Simpson index was not significantly different in any of the groups.The intestinal muscle thickness of Channa argus in the LBP1,LBP2,LBP3 groups was higher than that of the control group(P<0.05).The intestinal fold height and fold width of Channa argus in the LBP2,LBP3 groups were significantly higher than that of the control,LBP4,LBP5 groups(P<0.05).The expression levels of ZO-1 and claudin-3 genes in the intestine of LBP2,LBP3,and LBP4 groups were significantly higher than those of other groups(P<0.05).The protease activity of LBP3,LBP4 groups was significantly higher than all other groups(P<0.05),and the addition of LBP to the feeds all significantly increased amylase activity(P<0.05),and the intestinal lipase activity of Channa argus in LBP1,LBP2 groups was significantly increased compared with the control group(P<0.05).The intestinal superoxide dismutase(SOD)activity was increased in the LBP addition group(P<0.05),intestinal catalase(CAT)and glutathione peroxidase(GSH-Px)activities were significantly higher in the LBP3 group than in all other groups(P<0.05),and intestinal malondialdehyde(MDA)content was significantly lower in the LBP3 group than in all other groups(P<0.05).Compared with the control group,the gene expression levels of interleukin1β(IL-1β)and nuclear factor-κB(NF-κB)were reduced in the intestine of the LBP group(P<0.05),the gene expression of interleukin8(IL-8)and tumor necrosis factor-α(TNF-α)were significantly lower in the LBP2,LBP3,LBP4 groups compared with the control group(P<0.05),Compared with the control group,the intestinal interleukin10(IL-10),immunoglobulin T(Ig T),polyimmunoglobulin receptor(p Ig R)gene expression and Ig M levels were significantly higher in the LBP group(P<0.05),and the highest value was reached in the LBP3 group.(3)Effect of LBP in feed on the immune function of Channa argus.To study the effect of LBP on the immunity of Channa argus,serum,kidney and spleen tissues were taken after 56 d of feeding to detect immune-related indexes.The results showed that the serum,kidney and spleen lysozyme(LZM)activities of fish in the LBP2 and LBP3 groups were significantly higher than those in the control group(P<0.05),Compared with the control group,the kidney alkaline phosphatase(AKP)activity was significantly higher in the LBP added group(P<0.05),and the serum and spleen AKP activities were significantly higher in the LBP3,LBP4,LBP5 groups(P<0.05),Serum acid phosphatase(ACP)activity was significantly higher in the LBP3,LBP4 groups than in the control group(P<0.05),and spleen ACP activity was significantly higher in the LBP3 group than in the control group(P<0.05),while there was no significant change in renal ACP activity(P>0.05),Ig M levels in serum,kidney and spleen were higher in the LBP3 group than in the control group(P<0.05),Compared with the control group serum C3 was significantly higher in the LBP2 group(P<0.05),kidney C3 levels were significantly higher in the added LBP group(P<0.05),and spleen C3 levels were significantly higher in fish from the LBP1,LBP2,LBP3 groups(P<0.05),serum,kidney and spleen C4 were significantly higher in fish from the LBP2,LBP3 groups(P<0.05).The expression of IL-1β,IL-8,interleukin 12(IL-12),TNF-α and NF-κB genes were down-regulated in kidney and spleen,and the expression of IL-1β,IL-8,IL-12,toll like receptor 2(TLR2)and myeloid differentiation factor88(My D88)genes in kidney and spleen of LBP2,LBP3,LBP4 groups were significantly lower than that of control and LBP1 groups(P<0.05),the expression of TNF-α gene in LBP3 group gene expression in the LBP3 group was significantly lower than that in the other groups(P<0.05),NF-κB gene expression in the LBP3,LBP4 groups was significantly lower than that in the control group(P<0.05),IL-10 gene expression in the kidney and spleen of the LBP group was significantly higher than that in the control group,and that in the LBP3,LBP4 groups was significantly higher than that in the other groups(P<0.05).After Nocardia attack,the survival rate of LBP3 group was significantly higher than that of the control group(P<0.05).Under the conditions of this test,LBP improved the growth performance,feed utilization,intestinal barrier function and enhanced immunity of Channa argus.The results of the above indicators showed that the optimum LBP addition level for Channa argus feed was 1500-1587.05mg/kg. |
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