Effects Of Dietary Methionine Hydroxy Analogue On Digestive Ability, Antioxidative Ability And Immune Function Of Juvenile Jian Carp (Cyprinus Carpio Var.Jian)

A total of 900 juvenile Jian carp (Cyprinus carpio var. Jian) (8.24±0.03 g) were fed practical diets containing graded levels of methionine hydroxy analogue (MHA) (0,5.1, 7.6,10.2,12.7 and 15.3 g kg-1 diet) for 60 days to investigate the effects of MHA on digestive ability, antioxidative ability and immune function. After 60-day feeding trial, thirty fish with similar weight was remendaly slected from each treatment to conduct a challenge trial with Aeromonas hydrophila for 17 days.The results showed that MHA levels great significantly improved percent weight gain (PWG), feed intake (FI), protein production value (PPV) and lipid production value (LPV) (P<0.01), and slightly increased feed efficiency (FE) and protein efficiency ratio (PER) (P>0.05). The significant positive correlation existed between PWG and FE, FI (r1=+0.818, r2=+0.855, P<0.05). The path-analysis data indicated that FE and FI had great significantly direct on PWG. These data suggested that MHA improved growth by increasing FE and FI. The positive correlation also existed between FE and PER, PPV and LPV (r1=+0.990, P<0.01; r2=+0.936,P<0.01; r3=+0.811, P<0.05). These appeared that MHA improved feed utilization efficiency through promoting the utilization of protein and lipid in feed. MHA great significantly increased activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) in serum, 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=-0.913, P<0.01; r2=-0.933, P<0.01; r3=-0.849, 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. The data also showed that MHA great significantly improved hepatopancreas weight, intestine weight, intestine length, intestoSomatic index, trypsin, amylase, lipase, chymotrypsin in hepatopancreas and intestine, creatinekinase,γ-glutamyl transpeptidase and Na+, K+-ATPase activities in proximal intestine (PI), mid intestine (MI) and distal intestine (DI), alkaline phosphatase (AKP) in PI and DI (P<0.01), while significantly improved hepatoSomatic index, hepatopancreas protein content and folds height in PI, MI and DI (P<0.05). FE was positively correlated with creatinekinase, Na+, K+-ATPase and folds height in MI and DI (r1=+0.848; r2=+0.856; r3=+0.901; r4=+0.889; r5=+0.825, P<0.05), and FI was positively correlated with hepatopancreas protein content, trypsin and amylase in hepatopancreas and intestine, AKP in PI and DI (r1=+0.830, P<0.05; r2=+0.905, P<0.05; r3=+0.955; r4=+0.963; r5=+0.996; r6=+0.948; r7=+0.938, P<0.01; r8=+0.907, P<0.05). These appeared that MHA incredsed FE and FI by promoting the growth of hepatopancrea and intestine, as well as acitivities of digestive and absorptive enzymes. MHA level great significantly (P<0.01) or significantly (P<0.05) affected the malondialdehyde (MDA), protein carbonyl (PC) and glutathione (GSH) content, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST) and glutathione reducase (GR) in serum, muscle and hepatopancreas, anti-superoxide anion (ASA) in serum and intestine, anti-hydroxy radical (AHR) in serum and hepatopancreas, as well as MDA and protein carbonyl content, ASA, AHR, SOD, CAT, GPX and GR activities in muscle. MHA also great significantly increased the number of Lactobacillus and dreased the number of Escherichia coli (P<0.01). Meanwhile, MHA slightly increased vaccinated survival rate (P>0.05). Head kidney weight, hind kidney weight, spleen weight, red and white blood cell count, phago-rate of leukocytes, lysozyme, tartrate-resistant acid phosphatase (TRAP), addiment C3 and C4, serum total iron binding capacity, antibody titre to Aeromonas hydrophila were great significantly (P<0.01) or significantly (P<0.05) affected by MHA. Positive correlation existed between vaccinated survival rate and red and white blood cell count, head kidney weight, lysozyme, addiment C4/C3 and Bacillus acidi-lactici number (r1=+0.914, P<0.01; r2=+0.806; r3=+0.801; r4=+0.808; r5=+0.849; r6=+0.819; r7=+0.825, P<0.05). These results indicated that MHA improved body disease resistance by increasing various immune factors and the number of Lactobacillus.In conclusion, supplementation MHA to methionine deficiency diet promoted the growth of Jian carp. The optimal supplemental level of MHA for fish meal and miscellaneous meals based diet (measured with 0.69% methionine) based on PWG was 0.82% by the quadratic regression analysis. MHA increased digestive and absorptive ability of juvenile Jian carp by promoting digestive organs growth and digestive and absorptive enzymes activities, while the improved growth and function of digestive organs is partly due to the enhancement of antioxidantive ability in these organs by inceasing antioxidant enzymes activities and GSH content. Meanwhile, MHA also depressed lipid and protein oxidant in muscle, thus promoted antioxidant status of muscle in juvenile Jian carp. MHA promoted the balance of intestinal microflora in juvenile Jian carp by increasing the proliferation of Bacillus acidi-lactici and depressing the growth of Bacillus coli. MHA improved the non-specific immunity ability of juvenile Jian carp by promoting the phagocytosis ability of leukocytes and body sterilization ability, and improved specific immunity ability by enhancing the production of specific antibody.