Effects of dietary glutamine supplementation on growth performance, antioxidant status and intestinal function in juvenile grass carp (Ctenopharyngodon idella)

Glutamine (Gln) is a conditionally essential free amino acid that has been widely used in aquaculture. The present study showed that appropriate levels of dietary Gln could significantly improve growth performance and increase lipase and trypsin activity, mucosal thickness (MT) and the number of lymphocytes. The levels of glycine (Gly) in the 6 g/kg Gln group, threonine (Thr) in the 12 g/kg group and lysine (Lys) in the 6 and 9 g/kg group were increased significantly, while glutamate (Glu) and serine (Ser) concentrations decreased significantly with increasing dietary Gln levels from 3 to 12 g/kg. Moreover, the 12 g/kg dietary Gln level could improve the concentration of malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase (GSH-PX) and the total antioxidant capacity (T-AOC). In addition, 3 g/kg Gln upregulated the gene expression of aminopeptidase N (APN), caudal-related homeobox gene (CDX2), L-type amino acid transporter 2 (LAT2), oligopeptide transporter 1 (PEPT1), specificity proteins 1 (SP1) and 3 (SP3), and peroxisome proliferator-activated receptor α (PPAR-α) but downregulated PPAR-γ gene expression compared to that in the control group. Taken together, these findings suggest that Gln could improve the growth performance, antioxidant status and intestinal function of grass carp.