Effects Of Dietary Niacin On Digestive And Immune Function Of JuvenileJian Carp (Cyprinus Carpio Var.Jian)

This experiment was conducted to compare the effects of dietary niacin levels on digestive capability and immune function of juvenile Jian carp(cyprinus carpio var.Jian). A total of 900 Jian carps with an average initial weight of 13.95±0.04g were randomly distributed into each of 18 experimental aquarium(90×30×40cm³) connected to a closed recirculating water and oxygen auto-supplemented system.Six experimental diets containing graded levels of niacin(11.30,14.87,24.90,35.33,44.59 and 59.66 mg niacin/kg diet) were fed to triplicate groups of 50 fish for 10 weeks.After 10-week feeding,a challenge trial was couducted by injection of Aeromonas Hydrophila(AH) for 17 days to determine the effect of niacin on immune function of juvenile Jian carp.The results showed as follows:Jian carp fed the niacin deficiency diet(1-1) showed hemorrhage in skin and fins.hemorrhage on the mouth and eye.Niacin has great effect on weight gain(WG),feed intake(FI),feed efficiency(FE),protein production value(PPV), fat production value(FPV),ash production value(APV),calcium production value and phosphorus production value.There were significant correlation between weight gain and feed conversion efficiency,PPV,APV and APV(r=+0.665,P＜0.05;r=+0.816,P＜0.01; r=+0.775,P＜0.01;r=+0.810,P＜0.01),and there were significant correlation between FE and PPV,APV and APV(r=+0.828,P＜0.01;r=+0.927,P＜0.01;r=+0.811,P＜0.01).The path-analysis results indicated that FE had significant direct effect on WG(P0.1=0.9640, d0.1=0.9293,P＜0.01),and PPV had had significant direct effect on FE(P0.1=0.8022, d0.1=0.6435,P＜0.05).Hepatopancreas weight,intestine weight and intestine length,The protein contents of hepatopancreas and intestine,AKP,Na⁺,K⁺-ATP,CK,γ-GT,trypsin, chymotrypsin and lipase activities were significantly increased with the increase of dietary niacin levels(P＜0.01).There were significant correlation between PPV and activities of trypsin,chymotrypsin of intestine and trypsin of hepatopancreas(r=+0.806,P＜0.05; r=+0.94,P＜0.01;r=+0.946,P＜0.01).The survival rate after vaccination,hago-rate of leukocyte,lysozyme activity,ACP activity,the level of lectine,total iron-binding capacity and the contents of complement C3,complement C4 and immunoglobulin M were significantly increased with the increase of dietary niacin levels(P＜0.01).There were significant correlation between survival rate after vaccination and hago-rate of leukocyte, antibody level rate,lysozyme activity,ACP activity(r=+0.794,P＜0.01;r=+0.947,P＜0.01; r=+0.868,P＜0.01;r=+0.843,P＜0.05 ),and there were significant correlation between hago-rate of leukocyte and white cell population,red cell population,content of C3, lectine level(r=+0.897,P＜0.01;r=+0.930,P＜0.01;r=+0.582,P＜0.05;r=+0.946,P＜0.01). besides,there were significant correlation between white cell population,red cell population and spleen weight(r=+0.785,P＜0.01;r=+0.737,P＜0.01).The path-analysis results indicated that white cell population,content of C3,lectine level had significant direct effect on hago-rate of leukocyte(P_0.1=0.2821,d_0.1=0.0796,P＜0.01:P_0.3=0.1147, d_0.3=0.0132,P＜0.01;P_0.4=0.1596,d_0.4=0.0255,P＜0.01).In conclusion,the growh and development of digestive organs,the activities of digestive enzyme,the absorption ability of juvenile Jian Carp can be improved by niacin. Meanwhile,niacin strengthened innate immunity by improving the ability of pathogen recognition,opsonization,inhibition,lysis.Fish fed the niacin deficiency diet showed hemorrhage in skin,fins and on the mouth,and pathological change of hepatopancreas, heart were observed.Based on PWG,FE,acitivities of intestine Chymotrypsin,proximal intestine Na⁺,K⁺-ATPase,antibody level and hago-rate of leukocyte,Niacin requirements of juvenile Jian Carp were estimated to be 31.12,34.06,35.88,33.52,34.61,37.86 mg/kg diet respectivly.