Studies On Effects Of Dietary Threonine On Digestive Ability And Antioxidative Ability Of Sub-adult Grass Carp(Ctenopharyngodon Idella)

A total of600sub-adult grass carp (Ctenopharyngodon idella)(441.9±2.6g) were randomly assigned to6groups and fed diets containing graded levels of threonine (3.3,5.9,8.4,10.9,13.1and15.8g kg-1) for8weeks to investigate effects of threonine on digestive ability, antioxidative ability and meat quality.Weight gain (WG) of sub-adult grass carp was significantly improved by dietary threoniene (P＜0.05). Patterns of differences in percent weight gain, specific growth rate and feed intake were similar with that in WG. The feed efficiency (FE) of sub-adult grass carp fed with the basal diet was significantly lower than that of other treatment groups (P<0.05). The pattern of difference in protein efficiency ratio was similar with that in FE. Activities of GOT and GPT in muscle, hepatopancreas and serum of sub-adult grass carp were significantly affected by dietary threonine levels (P＜0.05). Dietary threonine significantly improved activities of trypsin, chymotrypsin, amylase and lipase in intestine and hepatopancreas, as well as activities of alkaline phosphatase, y-glutamyl transpeptidase and creatine kinase in three intestinal segments and activities of Na+K+-ATPase in proximal intestine and mid intestine (P<0.05). The activity of Na+K+-ATPase in distal intestine of sub-adult grass carp was not affected by dietary threonine levels (P＜.05). The intestine length, intestine weight, intestosomatic index, intestine protein content, hepatopancreas weight, hepatosomatic index and hepatopancreas protein content of sub-adult grass carp were significantly improved by dietary threonine (P<0.05). Dietary threonine did not have significantly influences on relative gut length of sub-adult grass carp (P>0.05). Threonine significantly (P<0.05) decreased the content of malondialdehyde (MDA) and protein carbonyl (PC) in intestine and hepatopancreas of sub-adult grass carp (P<0.05). The anti-superoxide anion capacity (ASA), anti-hydroxy radical capacity (AHR), glutathione (GSH) content and activities of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and glutathione reducase (GR) in intestine and hepatopancreas of sub-adult grass carp were significantly affected by dietary threonine levels (P<0.05). Dietary threonine significantly increased muscle crude protein content (P<0.05), while contents of crude fat and ash were decreased by threonine (P<0.05). The muscle moisture content of sub-adult grass carp was not affected by dietary threonine levels (P＜0.05. The rate of nH decline was decreased by dietary threonine (P＜005) The muscle cooking loss of sub-adult grass carp was not affected by dietary threonine levels (P>0.05). Threonine significantly increased the shear force of the muscle of sub-adult grass carp (P<0.05). Muscle and serum contents of MDA and PC were significantly decreased by threonine (P<0.05), while ASA, AHR, GSH content as well as activities of SOD, CAT, GST, GPx and GR were improved by threonine (P<0.05).In conclusion, threonine could improve the growth performance, digestive and absorptive ability and the meat quality of sub-adult grass carp. The improved digestive and absorptive ability and the meat quality may be related to the increased antioxidant ability of digestive organs and muscle. The optimal level of dietary threonine based on WG for sub-adult grass carp (441.9-1013.4g) was11.6g kg-1diet or41.5g kg-1protein by quadratic regression analysis.