Effects Of Dietary Phytic Acid On The Growth Performance,Intestinal Barrier And Immune Function As Well As The Potential Mechanisms In Grass Carp (Ctenopharyngodon Idella)

This study aimed to evaluate the influences of dietary phytic acid(PA)on the growth performance,intestinal health as well as related potential mechanisms in on-growing grass carp(Ctenopharyngodon idella).A total number of 540 healthy fish(120.56 ± 0.51 g)were selected and randomly distributed into six groups,with three replicates in each group.Fish were fed six semi-purified diets containing graded levels of PA(0-4.0%)for 60 days as a growth trial with the purpose to study the effects of PA on fish intestinal barrier function.Then a challenge trial was conducted by injecting fish with Aeromonas hydrophila for 6 days to investigate the influences of PA on fish intestinal immune function.The results displayed that compared with the control group(0% PA diet),≥ 3.2% PA suppressed on-growing grass carp growth performance [percent weight gain(PWG),feed intake and feed efficiency].Further study indicated that PA(1)reduced the oxidation resistance displayed as increasing intestinal MDA and PC contents,whereas decreasing GSH content and antioxidant enzymes activities,and down-regulating antioxidant enzymes m RNA levels(except GSTP1)partly associated with Nrf2 pathway;(2)aggravated apoptosis partially by up-regulating caspase-3,-7,-8,-9,Apaf-1,Bax,Fas-L and p38 MAPK,whereas down-regulating Bcl-2,IAP and Mcl-1 m RNA levels in fish intestine;(3)damaged intestinal tight junctions partly by down-regulating the m RNA levels of ZO-1,ZO-2b,occludin(only in the DI),claudin-b,-c,-f,-3c,-7a,-7b,-11,and up-regulating claudin-12(only in the DI),-15 a,-15 b and MLCK m RNA levels;(4)disrupted intestinal immune function by reducing intestinal LZ activities,the contents of C3,C4 and Ig M,as well as down-regulating the m RNA levels of hepcidin,liver-expressed antimicrobial peptide(LEAP)-2A,LEAP-2B andβ-defensin-1;(5)aggravated intestinal inflammatory responses partly through up-regulating intestinal pro-inflammatory cytokines gene expression including TNF-α,IL-1β(except in the DI),IFN-γ2,IL-8,IL-12p40,IL-15(except in the DI)and IL-17 D and down-regulating intestinal anti-inflammatory cytokines gene expression including TGF-β1,IL-4/13 A,IL-4/13 B,IL-10 and IL-11,which were partially related to NF-κB and TOR signaling pathways,respectively.In conclusion,certain levels of PA disrupted intestinal barrier and immune function and suppressed growth performance of on-growing grass carp.Finally,based on the broken-line analysis of PWG,the MDA and Ig M contents in the proximal intestine,the maximum tolerance levels of PA for on-growing grass carp(120-450 g)were estimated to be 2.17,1.91 and 1.47% diet,respectively.