| A total of 1200 juvenile Jian carp (Cyprinus carpio var. Jian) (8.76±0.02 g) were randomly assigned to 6 groups and fed diets containing graded levels of histidine (0.23%,0.44%,0.63%,0.86%,1.08%,1.27%of diet) for 60 days to investigate the effects of histidine on digestive ability, antioxidative ability and immune function. After 60-day feeding trial, thirty fish with similar weight was remendaly sleeted from each treatment to conduct a challenge trial with Aeromonas hydrophila for 17 days.The results showed that histidine levels great significantly improved percent weight gain (PWG) and specific growth rate (SGR) (P＜O.01). Patterns of differences in feed intake (F1), feed efficiency (FE), protein efficiency ratio (PER), protein retention efficiency (PRE) and lipid retention efficiency (LRE) were similar with that in SGR. Histidine significantly increased activities of glutamate-oxaloacetate transaminase (GOT) in serum, muscle and hepatopancreas (P<0.05), while the trend of glutamate-pyruvate transaminase (GPT) and plasma ammonia content is opposite. The data also indicated that dietary histidine significantly improved hepatopancreas weight, intestine weight, hepatopancreas and intestine protein content, trypsin, amylase, lipase, chymotrypsin activities in hepatopancreas and intestine, creatinekinase, y-glutamyl transpeptidase, alkaline phosphatase, Na+, K+-ATPase activities and folds heights in proximal intestine (PI), mid intestine (MI) and distal intestine (DI) (P＜O.05). Histidine significantly (P＜O.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 anti-superoxidc anion (ASA) activities in serum, intestine and hepatopancreas, anti-hydroxy radical (AHR) in serum and intestine, glutathione reducase (GR) in serum and hepatopancreas as well as MDA, PC and GSH content, ASA, GST and GR activities in head kidney, spleen and muscle, AHR in head kidney and muscle, SOD in head kidney and spleen, CAT in head kidney and muscle, GPx activities in spleen and muscle. Dietary histidine also significantly improved the growth of Lactobacillus and depressed the growth of Escherichia coli and Aeromonas (P<0.05). Meanwhile, histidine significantly increased vaccinated survival rate (P<0.05) and has great significantly (P<0.01) or significantly (P<0.05) effects on head kidney and spleen weight, red and white blood cell, addiment C3 and C4, immunoglobulin M count, phago-rate of leukocytes, lysozyme and acid phosphatase activities, serum total iron binding capacity and antibody titre to Aeromonas.In conclusion, histidine could promote the growth of Jian carp. The optimal level of dietary histidine based on SGR was 0.78%or or 2.38 g lOOg-1 protein by quadratic regression analysis. Dietary histidine enhanced the digestive and absorptive ability of juvenile Jian carp by promoting the growth of digestive organs and the activities of digestive and absorptive enzymes, whereas the benefits may be partly due to the enhancement of antioxidantive ability in these organs. Meanwhile, dietary histidine promoted antioxidant status of juvenile Jian carp by inceasing antioxidant enzymes activities and GSH content in muscle, improving the ability to resist free radicals and depressing lipid and protein oxidant. Optimum histidine levels also optimized the intestinal microflora of juvenile Jian carp, improved the non-specific immunity ability by promoting the phagocytosis ability of leukocytes and body sterilization ability, and improved specific immunity ability by enhancing the production of specific antibody, whereas the benefits may be partly due to the enhancement of antioxidantive ability in head kidney and spleen. |
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