Effects Of Dietary Methionine On Digestive And Absorptive Ability And Antioxidative Ability Of Young Grass Carp(Ctenopharyngodon Idell)

A total of900grass carp(Ctenopharyngodon idell)(259.0±0.48g) were randomly assigned to6treatments with30cages. Each treatment consisted of5duplications. Each cage was stocked with30fish. Six experimental diets containing graded levels of methionine (2.19,4.72,7.18,9.67,12.21and14.69g/kg respectively) were fed to900fish for49days to investigate the effects of methionine on digestive and absorptive ability and antioxidative ability of young grass carp(Ctenopharyngodon idell). After the feeding trial,15fish were obtained from each treatment to collect intestine, hepatopancreas and dorsal muscle to determine growth and development index in digestive organs, digestive and absorptive enzymes and antioxidant enzymes activities, non-enzymatic antioxidants content and meat quality index.PWG, FI, FE, SGR and PER were significantly improved by the graded levels of methionine. The activities of glutamate-oxaloacetate transaminase (GOT) in serum and muscle and glutamate-pyruvate transaminase (GPT) activity in serum were significantly reduced fed with increasing dietary methionine (P<0.01), however, the activities of GOT and GPT in hepatopancreas and the GPT activity in muscle increased when the diet were fed with graded levels of methionine.Methionine supplemention improved HW, IW, HPC, IPC and IL, the activities of trypsin, chymotrypsin, lipase in hepatopancreas and intestine and Na+,K+-ATP, γ-GT and AKP in PI and MI (P<0.01), while activities of amylase and creatine kinase reduced when the diet were fed with graded levels of methionine (P<0.01). Methionine supplemention significantly reduced the levels of malondialdehyde (MDA) and protein carbonyl (PC) in serum, hepatopancreas and muscle (P<0.01), while the PC levels increased in intestine (P<0.01). The anti-superoxide anion (ASA) and anti-hydroxy radical (AHR) activities in intestine, serum, hepatopancreas and muscle increased significantly with increasing dietary methionine (P<0.01). Methionine supplemention increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reducase (GR) and the glutathione (GSH) level in hepatopancreas and intestine (P<0.01), SOD, CAT and GPX and the GSH levels in serum, SOD, GST, GR and the GSH level in muscle (P<0.01), while the activities of glutathione-S-transferase (GST) in intestine, hepatopancreas and serum, GR activity in serum, CAT and GPX activities in muscle reduced with increasing dietary methionine (P<0.01). Methionine supplemention significantly improved the content of crude protein, crude fat, crude ash, increased the shearing force and pH in muscle, while the moisture and drip loss decreased (P<0.05).In conclusion, methionine supplemention significantly improved the growth performance of young grass carp, enhanced the digestive and absorptive ability by premoting the growth and development, increasing digestive and absorptive enzymes activities in hepatopancreas and intestine. Methionine supplemention depressed lipid and protein oxidation in serum, hepatopancreas, intestine and muscle, enhanced enzymatic and non-enzymatic antioxidant ability. Methionine supplemention enhanced meat quality by increasing the content of crude protein, crude fat, ash and shearing force and decreasing the water and drip loss. Based on SGR, methionine requirement of young grass carp was quantified to be10.41g/kg dry diet (34.71g/kg cude protein) in the present of1.61g/kg cystine.