Effects Of Dietary Pyridoxine On Growth Performance,the Health Status Of Intestinal,Body And Gill,and Flesh Quality As Well As The Mechanisms Of Young Grass Carp(Ctenopharyngodon Idella)

This study investigated the effects of pyridoxine(PN)on growth performance,the health status of intestinal,body and gill,and flesh quality as well as the mechanisms of young grass carp(Ctenopharyngodon idella).A total of 540 health grass carp(231.85 ±0.63 g)were fed six diets containing graded levels of PN(0.12,1.39,3.01,4.55 and 5.93 mg/kg diet)for 10 weeks to investigate the effects of PN on fish growth performance and muscle quality.After growth trial,fish were infection of Aeromonas hydrophila for 14 days to investigate the effects of PN on the health status of intestinal and body as well as the mechanisms,and infection of Flavobacterium columnare for 3 days to investigate the effects of PN on the health status of gill as well as the mechanisms,which might reveal the effects of PN on the health status of intestinal,body and gill as well as the mechanisms of fish.The results showed that compared with PN deficiency,optimal PN level increased feed intake(FI),feed efficiency(FE),percent weight gain(PWG)and specific growth rate(SGR)of young grass carp(P<0.05),suggesting that optimal PN level could improve the growth performance of young grass carp.Meanwhile,optimal PN level increased the ability against enteritis,skin hemorrhage and lesion as well as gill rot of young grass carp(P<0.05),which might be partly associated with the enhanced health staute of intestine,body and gill.Further investigation found that,(1)optimal PN level decreased intestine,head kidney,spleen,skin and gill reactive oxygen species(ROS),protein carbonyl(PC)and malondialdehyde(MDA)contents(P<0.05),alleviated DNA fragmentation,down-regulated the mRNA levels of cysteinyl aspartic acid-protease(caspase)-2,-3,-7,-8,-9,apoptotic protease activating factor-1(Apaf-1),Bcl-2 associated X protein(Bax),claudin-12,claudin-15a(rather than claudin-15b),Kelch-like-ECH-associated protein 1a(Keap1a)(rather than Keap1b),p38 mitogen-activated protein kinase(p38MAPK)and myosin light chain kinase(MLCK)(P<0.05),whereas up-regulated the activities and mRNA levels of antioxidant enzymes,mRNA levels of B-cell lymphoma protein-2(Bcl-2),myeloid cell leukemia-1(Mcl-1),inhibitor of apoptosis proteins(IAP),claudin-b,-c,-f,-3c,-7a,-7b and NF-E2-related factor 2(Nrf2)(P<0.05),which enhanced the structural integrity of intestine,head kidney,spleen,skin and gill of fish.(2)optimal PN level increased the activities of lysozyme(LZ)and acid phosphatase(ACP),the contents of complements(C3 and C4)and immunoglobulin M(IgM)(P<0.05),up-regulated the mRNA levels of hepcidin,liver-expressed antimicrobial peptide 2A(LEAP-2A),LEAP-2B,?-defensin-1,anti-inflammatory cytokines such as transforming growth factor ?1(TGF-?1),TGF-?2,interleukin 4/13A(IL-4/13A),IL-4/13B(except intestine and gill),IL-10 and IL-11,signaling molecular sunch as inhibitor of ?B?(I?B?),target of rapamycin(TOR)and ribosomal protein S6 kinases 1(S6K1)(P<0.05),whereas down-regulated the mRNA levels of pro-inflammatory cytokines such as tumor necrosis factor a(TNF-a)(except PI and DI),interferon ?2(IFN-?2)(except intestine),IL-1?,IL-6(except gill),IL-8(except spleen),IL-12p35,IL-12p40(except skin),IL-15 and IL-17D(except spleen)as well as signaling molecular sunch as nuclear factor kappa B p65(NF-KBp65)(rather than NF-NF-KBp52),c-Rel,I?B kinase ?(IKK?),IKK?(except head kidney,spleen and skin),(rather than IKKa)and eIF4E-binding proteins(4E-BP)(P<0.05),which enhanced intestine,head kidney,spleen,skin and gill immune function of fish.In addition,optimal PN level increased the contents of muscle crude protein,crude fat,hydroxyproline(Hyp),composition of free amino acid and fatty acid as well as pH value(P<0.05),decreased muscle water,cooking loss,shear force,lactate content,cathepsins B and L activities as well as ROS,PC and MDA contents(P<0.05),whereas increased the activities and mRNA levels of copper,zinc superoxide dismutase(CuZnSOD),manganese superoxide dismutase(MnSOD),catalase(CAT),glutathione peroxidases(GPx),glutathione-S-transferases(GST)and glutathione reductase(GR)as well as glutathione(GSH)content(P<0.05),up-regulated the mRNA levels of Nrf2,TOR,S6K1,casein kinase 2a(CK2a)and CK2?,and down-regulated the mRNA level of Keapla(P<0.05),which enhanced the flesh quality of fish.As stated above,optimal PN level could enhance the ability against enteritis,skin hemorrhage and lesion as well as gill rot,improving the growth performance of young grass carp.The increased ability of against disease by optimal PN level might be partly related to the decreased intestine,head kidney,spleen,skin and gill ROS,PC and MDA contents,and up-regulated the mRNA levels of antioxiadant enzymes and tight junction proteins,down-regulated the cell apoptosis related indices,which under the regulation of Nrf2,MLCK and p38MAPK,respectively.In addition,optimal PN level increased intestine,head kidney,spleen,skin and gill antibacterial substance acitivities or contents,down-regulated pro-inflammatory cytokines and up-regulated anti-inflammatory cytokines mRNA levels under the regulation of NF-?B and TOR signaling,respectively.Furthermore,optimal PN level enhanced flesh quality partly relating to the increased nutrient content,physical parameter and antioxidant ability.Finally,in this study,based on PWG,and the ability against enteritis,skin hemorrhage and lesion as well as gill rot,optimal PN requirements for young grass carp were estimated to be 4.43,4.75,4.62 and 4.85 mg/kg diet,respectively.