| Intestinal tract is responsible for animal nutrition absorption and mucosal barrier resistance.Intestinal health determines the overall health of animals and the performance of production.The relationship between nutrition and intestinal health has always been the hot topics in traditional nutrition research.As we all know,starch has a protein-saving effect and is also used as an adhesive in the production of aquatic feed.At present,it is generally believed that fish have limited ability to utilize starch,and high carbohydrate diet will damage intestinal tight junction function and increase intestinal permeability,and at the same time,it will also lead to changes in intestinal flora and metabolism and then damage the normal intestinal barrier function.High amylose starch is a new type of dietary fiber with strong anti-digestibility.It is worth exploring whether the dietary branch/amylose ratio can be regulated to regulate the intestinal health of fish.Therefore,this study to largemouth bass as experimental object,by studying the different level of starch and structure on the growth performance,nutrient utilization,intestinal morphology,oxidation resistance,immunity levels,and the influence of intestinal flora,explore fish in intestinal health of dietary starch nutrition and nutrition stress response and verify the feasibility of using high amylose control fish intestinal health,in order to optimize the technical data of largemouth bass.1.Effects of dietary starch level on growth and intestinal health of largemouth bassThree isonitrogenous and isolipid experimental diets containing 5%,10% and15% corn starch were fed to largemouth bass(IBW:8.66±0.04g)for 8 weeks,respectively.The results showed that 15% starch level significantly inhibited the growth of largemouth bass,decreased the villus height,width and number of cup cells in midgut(P<0.05),and down-regulated the expression levels of intestinal tight junction-related genes ZO-1,Claudin-4 and Claudin-5(P<0.05).Plasma endotoxin content and diamine oxidase activity were significantly increased with dietary starch level increasing(P<0.05).Compared with 5% and 10% starch level groups,15% starch diet significantly decreased the activities of intestinal SOD and CAT,and down-regulated the expressions of antioxidase-related genes Nrf2,CAT and SOD(P<0.05).Meanwhile,the expression levels of pro-inflammatory cytokines(IL-8,IL-1βand TNF-α)and anti-inflammatory cytokines(IL-10 and TGF-β1)were significantly increased with dietary starch level increasing(P<0.05).In addition,dietary starch level increased significantly decreased the abundance of Lactobacillus,a probiotic bacteria,and induced an increase in the abundance of Brevundimonas and Ralstonia,potential pathogenic bacteria.Phenotypic prediction of intestinal flora by Bugbase tool showed that the abundance of Gram-negative bacteria in 15% starch group was significantly higher than that in 5% starch group(P<0.05),and the abundance of bacteria with potential pathogenicity was significantly higher than that in other groups(P<0.05).The contents of short-chain fatty acids,acetic acid and butyric acid in intestinal feces of15% starch group were significantly lower than those of 5% starch group(P<0.05).In conclusion,15% starch can inhibit the intestinal immunity and antioxidant capacity of largemouth bass,impair intestinal health,and thus affect its growth performance.At the same time,it will also cause the imbalance of intestinal microbiota and the decrease of short-chain fatty acids,which may also lead to the damage of intestinal function.2.Effects of dietary starch structure on intestinal health of largemouth bassIn order to study the influence of the starch structure of fish intestinal health,juvenile largemouth bass with similar initial body weight(8.53±0.06g)were fed an isonitrogenous and isolipid diet containing 10% common corn starch(amylose content:27%)and high amylose corn starch(amylose content: 69%)for 8 weeks,respectively.The results showed that SGR and PER of largemouth bass in high amylose group were significantly increased(P<0.05).The villus height,muscular thickness and goblet cell number of midgut and hindgut were not affected by starch structure,but the villus width of midgut and hindgut were significantly increased by high amylose content(P<0.05).High amylose significantly increased the expression level of intestinal gene ZO-1(P<0.05),but had no significant effect on the expression of Claudins and Occludin(P>0.05).Meanwhile,dietary high amyloss significantly increased the activities of CAT and SOD in intestinal tract,and up-regulated the expression levels of antioxidant related genes(Nrf2,SOD,CAT)and pro-inflammatory cytokines(TNF-α,IL-8)(P<0.05).In addition,high amylose content significantly decreased intestinal microflora abundance correlation index(Chao1)and diversity correlation index(Shannon and Simpson)(P<0.05).In terms of flora composition,dietary high amylose significantly increased the abundance of Firmicutes and Cyanobacteria in phylum level(P<0.05),and increased the abundance of beneficial bacteria such as Streptophyta and Lactobacillus in genus level(P<0.05).The microbial phenotype prediction by Bugbase tool showed that high amylose significantly decreased the abundance of potential pathogenic bacteria(P<0.05).In conclusion,high amylose starch can effectively improve the intestinal morphology,antioxidant capacity and immune level of largemouth bass,and then improve the structure and function of intestinal microflora,thus promoting the growth of largemouth bass. |
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