Effects Of Leucine On Growth Performance And Immune Of Juvenile Jian Carp (Cyprinus Carpio Var. Jian)

This experiment was conducted to study the effects of dietary leucine levels on growth performance, functions of digestion, absorption and immune of juvenile Jian carp (Cyprinus carpio var. Jian). In trial,1200 juvenile Jian carps with initial body weight 7.88±0.02 g were randomly allocated to 6 experimental groups with 4 replicate, feeding purified diets containing leucine0.76,0.95,1.17,1.36,1.55,1.77%DM for a 9 weeks growth trial. 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.The results showed that leucine levels great significantly improved percent weight gain (PWG), feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER) protein production value (PPV) and lipid production value (LPV) (P<0.01). Simultaneously, blood hematocyte counts, survival after vaccination, phagocytosis of leucocyte, immunoglobulin M (IgM) levels, anti-AH antibody titers, serum lectin titers, serum complement C3 and C4 levels, total iron-binding capacity and tartrate-resistant acid phosphatase (TRAP) and lysozyme were enhanced by graded leucine levels (P<0.01).The significant positive correlation existed between PWG and FE, FI (r1=+0.994, r2=+0.995, P<0.01). The path-analysis data indicated that FE and FI had great significantly direct on PWG. These data suggested that leucine improved growth by increasing FE and FI. The positive correlation also existed between FE and PER, PPV and LPV (r1=+0.996,P<0.01; r2=+0.989, P<0.01; r3=+0.958, P<0.01). These appeared that leucine improved feed utilization efficiency through promoting the utilization of protein and lipid in feed. Leucine great significantly increased activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) in muscle and hepatopancreas, while the trend of plasma ammonia content is opposite. Negative correlation existed between plasma ammonia content and activities of GOT in hepatopancreas and GPT in muscle and hepatopancreas (r1=-0.978, P<0.01; r2=-0.834, P<0.05; r3=-0.822, P<0.05). These suggested that the reduction of plasma ammonia content was correlated with the improvement of GOT and GPT activities in muscle and hepatopancreas. Positive correlation existed between vaccinated survival rate and phagocytosis of leucocyte, immunoglobulin M (IgM) levels, red blood cell count, serum complement C3 and C4 levels, total iron-binding capacity and tartrate-resistant acid phosphatase (TRAP) and lysozyme (r1=+0.806, P<0.05; r2=+0.970, P<0.01; r3=+0.875, P<0.05; r4=+0.912, P<0.05; r5=+0.833, P<0.05; r6=+0.893, P<0.05; r7=+0.857, P<0.05; r8=+0.887, P<0.05). There have a positive correlation existed between phagocytosis of leucocyte and red blood cell count immunoglobulin M (IgM) levels, serum lectin titers, serum complement C3 and C4 levels and tartrate-resistant acid phosphatase (TRAP) and lysozyme (r1=+0.864, P<0.05; r2=+0.813, P<0.05; r3=+0.943, P<0.01; r4=+0.832, P<0.05; r5=+0.877, P<0.05:r6=+0.938, P<0.01).These results indicated that leucine improved body disease resistance by increasing various immune factors.In considering these results, leucine improved the FI and FER to enhance the growth performance of juvenile Jian carp. Leucine improved the non-specific immunity ability of juvenile Jian carp by promoting the phagocytosis ability of leukocytes and body sterilization ability, and leucine increased anti-AH titers and sim-IgM levels so as to enhance specific immune ability. By the broken-line analysis the optimum dietary leucine requirement for optimal growth of juvenile Jian carp (7.88-26.00 g) was determined to be 12.9g kg-1 according to PWG.