Effects Of Thiamin On Growth Performance, Functions Of Digestion, Absorption And Immune Of Juvenile Jian Carp (Cyprinus Carpio Var. Jian)

This experiment was conducted to study the effects of dietary thiamin levels on growth performance,functions of digestion,absorption and immune of juvenile Jian carp(Cyprinus carpio var.Jian).Semi-purified diets with seven levels(0.25,0.48,0.79,1.06,1.37,1.63 and 2.65 mg thiamin kg^-1) of supplemental calcium d-pantothenate were fed for 9 weeks to triplicate groups of 50 fish(initial weight 8.20±0.02 g,mean±SD).After the growth trial, 30 fish in each treatment were randomly assigned to a challenge trial conducted by injection of Aeromonas Hydrophila(AH) for 17 days.Results indicated that within 6 weeks Jian carp fed with the thiamin-unsupplemented diet exhibited anorexia,poor growth,congestion of the fins,and congestion of the skin. Thiamin also improved percent weight gain(PWG),feed efficiency ratio(FER),protein efficiency ratio(PER),protein productive value(PPV),lipid deposition(LPV), hepatopancreas weight(HSW),hepatopancreas protein content(HPC),intestine weight (ISW),intestine protein content(IPC),intestine length(IL),intestinal folds height,activity of tryspin,chymotrypsin,lipase,amylase in hapatopancreas and intestine,and intestine brush border enzymes containing alkaline phosphatase(AKP),Na⁺,K⁺-ATPase and gamma-glutamyl transpeptidase(γ-GT)(P＜0.01 or P＜0.05).Simultaneously,immune organ weight,blood hematocyte counts,survival after vaccination,phagocytosis of leucocyte,sim-immunoglobulin M(sim-IgM) levels,anti-AH antibody titers,serum lectin titers,serum complement C3 and C4 levels,total iron-binding capacity and activity of serum acid phosphatase(ACP) and lysozyme were enhanced by graded thiamin levels (P＜0.01 or P＜0.05).Moreover,quantities of Bacillus acidi-lactici in intestine were affected by dietary thiamin levels(P＜0.01).Correlation analysis showed PWG,and FER were all positive related to the growth and development of hepatopancreas and intestine and digestive enzyme activities(P＜0.01 or P＜0.05),and survival after vaccination was directly correlated with phagocytosis of leucocyte,lysozyme,serum ACP,serum sim-IgM, serum and serum iron binding capacity(r₁=+0.777,P＜0.05;r₂=+0.822,P＜0.01; r₃=+0.829,P＜0.01;r₄=+0.873,P＜0.01;r₅=+0.876,P＜0.01).Path analysis indicated FI and FER had significantly direct effects on percent weight gain(P_0.1=0.484,d_0.1=0.232; P_0.2=0.532,d_0.2=0.274),which demonstrated the promoted effects of dietary thiamin on the growth were closely to the enhanced feed intake and feed efficiency ratio;trypsin and lipase in intestine had significantly direct effects on FER(P_0.1=0.326,d_0.1=0.106,P＜0.01; P_0.2=0.562,d_0.2=0.316,P＜0.01),which means the supplement of thiamin improved the digestive function of juvenile Jian carp through increasing the digestive enzyme activities. There was a direct effect of white cell population and red cell population on phago-rate of leukocyte,,which expressed thiamin improved enhance non-specific immune ability of juvenile Jian carp by enhancing white cell population and red cell population;there also had a significant effect of red cell population and serum complement C3 on sim-IgM levels after vaccination(P_0.1=0.373,d_0.3=0.139,P＜0.01;P_0.2=0.590,d_0.2=0.348,P＜0.01),which meant there was a major indirect and positive correlation between them.In considering these results,thaimin improved the ability to digesting and absorbing nutrients to promote FI and FER though advancing the growth and development of digestive organs,the ability to secreting digestive enzymes and activity of intestinal enzymes and intestine brush border enzymes,so as to enhance the growth performance of juvenile Jian carp.At the same time,thaimin promoted phagocytosis of leucocyte, enhanced activity of serum lysozyme and ACP,serum iron-binding capacity,serum lectin titers,serum complement C3 and C4 levels,increased Bacillus acidi-lactic counts in intestine in order to enhance non-specific immune ability of juvenile Jian carp;thiamin increased anti-AH titers and sim-IgM levels so as to enhance specific immune ability.By the broken-line analysis the optimum dietary thiamin requirement for optimal growth of juvenile Jian carp(8.20-60.22 g) was determined to be 1.02 mg kg^-1 according to PWG. Maximum activity of tryspin and lipase was achived at the level of 1.08 and 0.80 mg thiamin kg^-1,respectively.Maximum activity of AKP in forgut and midgut was achived at the level of 1.04 and 1.12 mg thiamin kg^-1,respectively.White body cell count,serum iron-binding capacity,activity of serum lysozyme,sim-IgM levels and phagocytosis of leucocyte obtained maximum values when the thiamin level was at 1.03 mg kg^-1,1.06 mg kg^-1,0.84 mg kg^-1,0.81 mg kg^-1 and 1.00 mg kg^-1,respectively.