Effects Of Dietary Biotin On Growth Performance,Immune Function And Structural Integrity As Well As The Mechanisms Of Head Kidney And Spleen In On-growing Grass Carp(Ctenopharyngodon Idella)

Our study investigated the effect of dietary biotin on growth performance,the health status of head kidney,spleen and skin as well as further explored involved mechanisms in on-growing grass carp(Ctenopharyngodon idella).Six groups(thirty grass carps per repetition and three repetitions per group)of grass carp(average initial weight:117.11 ± 0.48 g)were fed six diets containing graded levels of biotin(0.012,0.110,0.214,0.311,0.427 and 0.518 mg/kg diet)for 10 weeks to explore the influences of biotin on fish growth performance.Experimental period include growth trial(ten weeks)and challenge trial(six days).The results showed that compared with biotin deficiency group,appropriate biotin level increased PWG,SGR,FI and FE(P < 0.05),suggesting that biotin could improve the growth performance of grass carp.Meanwhile,appropriate biotin level increased the capacity of against skin hemorrhage and lesion in on-growing grass carp(P < 0.05).Further investigation found that biotin could enhance immune function and stuctural integrity of immune organs in on-growing grass carp:(1)Appropriate level of biotin increased innate immune-related factors ACP and LZ activities,C3,C4 and adaptive immune of IgM contents(P < 0.05),up-regulated mRNA levels of antimicrobial peptides(such as LEAP-2A/2B,hepcidin and ?-defensin-1),meanwhile up-regulated anti-inflammatory cytokines(such as TGF-?1)(rather than TGF-?1),IL-4/13A(rather than IL-4/13B),IL-10 and IL-11] mRNA levels(P < 0.05),related signaling molecules(such as TOR,S6K1,I?B?)and protein levels of p-TOR Ser2448 and T-TOR(P < 0.05),down-regulated pro-inflammatory cytokines [such as TNF-?,IFN-?2,IL-1?,IL-6,IL-8 and IL-12 p40(IL-12 p35),IL-15 and IL-17D] as well as related signaling molecule nuclear factors [such as NF-?Bp65,NF-?Bp52,c-Rel,IKK? and IKK?(rather than IKK?)] mRNA levels and protein levels of NF-?Bp65 in the head kidney,spleen and skin of on-growing grass carp(P < 0.05).(2)Appropriate level of biotin decreased MDA,PC and ROS contents(P < 0.05);increased the activities of ASA,AHR and antioxidant enzyme(such as GR,GPx,CuZnSOD,MnSOD,CAT and GST)as well as the content of GSH(P ? 0.05);up-regulated the mRNA levels of of CuZnSOD(rather than MnSOD),GPx1a/b(rather than GPx4a/b),GST and GR(P < 0.05),and up-regulated the mRNA levels of NF-E2-related factor 2(Nrf2)(P < 0.05),down-regulated the mRNA levels of Keap1a/b in the immune organs of on-growing grass carp(P < 0.05),suggesting that biotin could enhance the antioxidant ability and reduce the oxidative damage in immune organs of on-growing grass carp.(3)Appropriate level of biotin could up-regulate IAP,Mcl-1 and Bcl-2 mRNA levels(P < 0.05),down-regulate Bax,Apaf-1,caspase-2/-/3/-7/-8/-9,FasL and p38MAPK(rather than JNK)mRNA levels,suggesting that biotin could inhibit the excessive apoptosis in head kidneys,spleen and skin in on-growing grass carp.(4)Appropriate level of biotin up-regulated the mRNA levels of ZO-1,ZO-2(except for spleen),occludin,claudin-c,-f,-7 and-11,while down-regulated claudin-12 and MLCK mRNA levels,indicating that biotin could preserve the intercellular structural integrity in immune organs of grass carp.To sum up,biotin could enhance inmmune function,structural integrity in inmmune organs and growth performance of on-growing grass carp.Under this experimental condition,based on the growth performance(PWG),disease resistance of skin lesion,the biotin requirements for grass carp were calculated to be 0.210 and 0.230 mg/kg diet,respectively.