Effects Of Compound Antimicrobial Peptides Feed On Growth Performance,Antioxidant Activity,and Immunity Of Grass Carp (Ctenopharyngodon Idellus)

Compound antimicrobial peptides was added to the basal diet of grass carp(Ctenopharyngodon idellus)to study the effects of compound antimicrobial peptides on grass carp growth performance,antioxidant and digestive enzyme activities,intestinal structure and microflora,as well as tissue immune-related gene expression.Six treatment groups including one control group(without compound antimicrobial peptides)and five additional groups: F1(100 mg/kg),F2(200 mg/kg),F3(400 mg/kg),F4(800 mg/kg),and F5(1600mg/kg).The fish were cultured for 8 weeks.The results were as follows:(1)When the dose of compound antimicrobial peptides was 800 mg/kg,the mean weight,specific growth rate,and relative weight gain of grass carp were significantly higher than the control group(P < 0.05).There was no significant difference in feed coefficient and survival rate between groups(P > 0.05).(2)Compound antimicrobial peptides could affect the amylase activity of grass carp.The amylase activities of F2 to F4 groups in the intestine were significantly increased than other groups(P < 0.05).And the amylase activities of F2,F3,and F5 groups in the hepatopancreas were significantly increased than other treatment groups(P < 0.05).In addition,the activities of lipase and chymotrypsin in the hepatopancreas and intestine in all the groups that added with Compound antimicrobial peptides were significantly higher than the control group,while the chymotrypsin activity in the F2 group in the intestine was significantly increased than that in other groups(P < 0.05).(3)In the hepatopancreas of grass carp,the T-AOC activities in the F3 and F4 groups were significantly increased than the control group and other additive groups.And the MDA activities in the groups that added with compound antimicrobial peptides were significantly decreased than the control group(P < 0.05),In addition,the SOD activities in the group that added with compound antimicrobial peptides were significantly higher than the control group,with the F5 group was significantly increased than other groups(P < 0.05).However,in the intestine,the T-AOC activities in the F4 and F5 group were significantly increased than the other groups(P < 0.05),between which the activity of F4 group was the highest.And the MDA activities were fluctuated in intestine,but the F5 was significantly decreased than the other groups.In addition,the SOD activity was not significantly different in all the groups,but was highest in group F4.(4)The height of proximal villi in the F4 group was the highest.The heights of middle villi in the F4 and F5 group were significantly increased than the other groups(P < 0.05).In addition,the depths of the proximal in the groups that was added with compound antimicrobial peptides were significantly decreased than the control group(P < 0.05),with the depth of the middle was the lowest in the F4 group.The depths of middle were fluctuated,with the lowest and the highest in the F3 and F5 groups,respectively.Moreover,the V/C values of proximal and middle in the F4 group were significantly higher than the control group(P < 0.05).Lastly,there was no significant difference in the distal villi height,crypt depth,and V/C value between all the groups(P > 0.05).(5)The mean relative abundance of Firmicutes in the intestinal tract of grass carp in the F3 and F4 groups was significantly increased than the control group,while the mean relative abundance of Oxyphotobacteria in the F1 and F5 groups was significantly increased than the control group(P < 0.05).The mean relative abundance of Planctomycetacia in the all the group added with compound antimicrobial peptides except(F2)was significantly decreased than the control group.As for Fusobacteriia,the proportion of the mean relative abundance in the F4 group was the smallest compared with all other groups.(6)The m RNA expression levels of Mn SOD in the hepatopancreas and the spleen in the F3 group were significantly increased than the control group(P < 0.05).And there was no significant difference between the groups other than F3 group and the control group(P >0.05).In the kindey and the intestine,there was no significant difference in terms of Mn SOD mi RNA expression level.(P > 0.05),but the expression of Mn SOD in F3 group was higher than that in other groups.(7)In the hepatopancreas,the m RNA levels expression levels of IL-8 and TNF-α in the F3 group were significantly increased than the F4 and F5 groups(P < 0.05).And the m RNA expression levels of anti-inflammatory factor TGF-β in the F3 group was significantly decreased than the control group and the F4 group(P < 0.05).Additionally,the m RNA expression levels of IL10 in the F3 group was the lowest in all groups,which was significantly decreased than the F5 group(P < 0.05).However,in the spleen,the m RNA expression levels of IL-1β in the F3 group was significantly increased than the control group(P < 0.05).And m RNA expression levels of TNF-α and IL8 in the F3 group were significantly increased than that in the F4 group(P < 0.05).In addition,the m RNA expression levels of anti-inflammatory factors IL10 and TGF-β were significantly increased than the control group(P < 0.05),and moreover,TGF-β was also significantly decreased than the F4 group(P < 0.05).(8)In the kidney,he m RNA expression levels of IL-1β and TNF-α in the F3 group was significantly increased than that in control group(P < 0.05),while TNF-α m RNA expression level in F5 group was also significantly increased than the control group(P < 0.05)and IL8 showed no significant difference among all groups(P < 0.05).In summary,the expression trend of anti-inflammatory factors in kidney were consistent with that in spleen.And the expression trends of IL-1β,IL8,TNF-α,IL10,and TGF-β in the intestine were similar to those in the spleen.In conclusion,the results showed that the addition of compound antimicrobial peptides(400-800 mg/kg)could improve the growth performance,anti-oxidation and digestion ability of grass carp,improve the diversity of intestinal tissue and microflora,and enhance the expression of immune-related genes.