Effects Of Dietary Glycinin Or β-conglycinin Addition On The Growth Performance And Intestinal Health Of Grouper (Epinephelus Coioides)

A feeding trial was conducted to investigate whether glycinin or β-conglycinin addition in the feed affect the growth performance and intestinal health of grouper Epinephelus coioides.The control diet(FM diet)was formulated to contain 48% protein and 11% lipid.Soybean meal was used to replace 60 % fish meal protein in FM diet to prepare soybean meal ditet(SBM diet)as the positive control diet.Glycinin at 4.5% glycinin(G-4.5)and 10% glycinin(G-10)orβ-conglycinin at 3% β-conglycinin(β-3)and 7% β-conglycinin(β-7)were added to the FM diet to prepare four experimental diets.The fish with an initial weight of 8.01±0.10 g were randomly divided into 18 tanks,20 fish per tank.Six experimental groups of fish were fed to apparent satiety twice daily during a feeding period of eight weeks.The main results are as follows:(1)Growth performance: the WGR and SGR of grouper in the FM,G-4.5 and β-3 groups were significantly higher than those in the G-10,β-7 and SBM group(P<0.05),while the HSI of the FM group was significantly higher than other groups(P <0.05);the FI of G-10 and β-3groups were significantly higher than SBM group.(2)Whole body composition: the content of whole body moisture in the SBM group was significantly higher than that of FM,G-4.5,β-3(P <0.05);the contents of whole body crude ash of fish in SBM,G-10,and β-7 groups were significantly lower than that in the FM group(P<0.05),but the contents of whole body crude lipid was significantly lower than that in the FM,G-4.5 group(P<0.05).There was no significant difference in the content of whole body protein among groups(P>0.05).The growth performance and whole body composition were affected by both the type of soybean antigen protein and the level of dietary addition.(3)Antioxidant capacity of the liver: the activities of T-AOC in the FM,G-4.5 and β-3groups were significantly higher than that in the β-7,and SBM groups(P<0.05);the activity of GSH-Px was significantly higher than SBM group(P<0.05),and significantly lower than that of other groups(P<0.05),while the MDA content was significantly lower than that of the G-10,β-7,and SBM groups(P<0.05),and significantly higher than other groups(P<0.05).The activities of the T-AOC and GSH-Px had the lowest value,and the MDA content had the highest value in the SBM group among groups.There was no significant difference in activities of CAT and SOD among groups(P>0.05).The antioxidant capacity of the liver was affected by adding levels of soybean antigen protein,but was not affected by the type of soybean antigen protein.(4)Morphology and structure of intestinal tract: the muscle thickness of midgut in the FM,G-4.5 and β-3 groups were significantly higher than that in the SBM group(P<0.05),and the muscle thickness of hindgut was significantly higher than that in the SBM and β-7 groups(P<0.05).And compared with the FM,G-4.5 and β-3 groups,the G-10,β-7,and SBM groups had higher intestinal mucosa fold height(P<0.05).There was no difference in the number of mucosal folds in each intestinal segment among groups(P>0.05).The m RNA levels for occludin in β-3 group was significantly higher than that in SBM,G-4.5,G-10 and β-7 groups(P<0.05),and the m RNA levels for claudin-3 was significantly higher than in SBM,G-10 and β-7 groups(P<0.05).The m RNA levels for ZO-1 in the FM,G-4.5 and β-3 groups were significantly higher than that in the G-10,β-7,and SBM groups(P<0.05).The intestinal morphology and the tight junction structure of grouper were affected by the addition level of soybean antigen protein,and the intestinal morphology affected only by soybean antigen protein type.Compared to the FM group,the quantity of goblet cells in mid and hind gut in soybean antigen protein addition groups were reduced,the lamina propria was widened and accompanied by lymphocyte infiltration;migrated disordered nuclei arrangement of monolayer columnar epithelial cells,and shortened mucosal folds in hindgut mucosa.(5)Intestinal mucosal permeability: the activity of DAO,the contents of D-Lac and ET in G-10,β-7,and SBM groups were significantly higher than those in FM,G-4.5 and β-3 groups(P<0.05).The SBM group had the highest value among groups.The permeability of the intestinal mucosa was affected by the adding level of soybean antigen protein in the feed,and not affected by the type of soybean antigen protein.(6)Intestinal cell apoptosis: the quantity of intestinal cell apoptosis in the SBM,G-10 andβ-7 groups were significantly higher than that in the FM,G-4.5 and β-3 groups(P<0.05),and the quantity of apoptotic cells in SBM had the highest value.But there was no difference in apoptotic cells of the foregut among groups(P>0.05).The m RNA levels for caspase-3,caspase-8 and caspase-9 in the SBM,G-10 and β-7 groups were significantly higher than that in the FM,G-4.5 and β-3 groups(P<0.05),and the SBM group had the highest value.The m RNA levels for bcl-2 and bcl-x L were significantly lower than that in the FM,G-4.5 and β-3 groups(P<0.05),and the SBM group had the lowest value.The expression of intestinal cell apoptosis genes was affected by the adding level of soybean antigen protein in the feed,and not affected by the type of soybean antigen protein.(7)Intestinal microbes: Alpha diversity index OTUs,Chao1,Ace,Shannon and Simpson were not affected by the levels of soybean antigen protein(P>0.05).At the phylum level,the dominant flora of all groups were Proteobacteria,Tenericutes,Actinobacteria and Firmicutes respectively.The Tenericutes counts in FM and β-3 groups were significantly higher than that of other groups.The SBM group had the lowest abundance of Firmicutes.At the genus classification level,the dominant bacteria are Achromobacter,Arthrobacter and Vibrio,respectively.The SBM group had the highest abundance of Vibrio.(8)The gene expression of intestinal inflammatory factors: the m RNA levels for IL-1β,NF-κB1(P50),My D88,IL-8 and TNF-α in G-10,β-7 and SBM groups were significantly higher than that in FM,G-4.5 and β-3 groups(P<0.05);the m RNA levels for IKK-α,TAK1,Rel A(P65)in G-10,β-7,and SBM groups were significantly higher than that in FM and G-4.5 groups(P<0.05),but was not different from that in β-3 group(P>0.05);the m RNA levels for IκBa and TGF-β1 in FM,G-4.5 and β-3 groups were significantly higher than that in G-10,β-7 and SBM.The IL-10 m RNA levels in FM and β-3 groups were significantly higher than that in β-7 group.The expression of the intestinal immune inflammatory factor genes was affected by soybean antigen protein addition in the feed,but was not affected by the type of soybean antigen protein.The above results indicate that there were different effects of dietary glycinin orβ-conglycinin addition on the growth performance of grouper.Lower levels of glycinin orβ-conglycinin in diets did not reduce the grouper growth,but higher levels of them could limit their growth.The higher levels of soybean antigen protein in the feed decreased the liver antioxidant capacity,damaged the intestinal morphological structure,improved the intestinal mucosal permeability,and the number of intestinal cell apoptosis,destroyed the intestinal microbiota balance,and reduced the immunity of grouper.All in all,the dietary high level of soybean antigen protein had negative effects on the growth performance,body composition,liver antioxidant capacity and intestinal health of grouper.