Effect of Dietary Alanyl-glutamine Supplementation on Growth Performance, Development of Intestinal Tract, Antioxidant Status and Plasma Non-specific Immunity of Young Mirror Carp (Cyprinus carpio L.)

Exogenous alanyl-glutamine (Aln-Gln) was evaluated for its effects on growth performance, intestinal structure and function, antioxidant status and non-specific immunity of young carp (Cyprinus carpio L.). Six diets supplemented with 0, 2.5, 5.0, 7.5, 10.0, or 15.0 g · kg−1 of Aln-Gln were fed to fish for 12 weeks. Supplementation with 7.5, 10.0, or 15.0 g · kg−1 of Aln-Gln significantly increased weight gain rate (WGR), protein efficiency ratio (PER), but feed conservation rate (FCR) and survival were not affected (P>0.05). The intestinal fold height and number, digestive enzyme, Na+, K+-ATPase activities was found to be significantly high (P<0.05) with increasing dietary Aln-Gln supplementation up to 7.5 g · kg−1, but there were no significant differences for Aln-Gln supplementation from 7.5 to 15.0 g · kg−1. The glutathione peroxidase (GPX) activity, glutathione (GSH), superoxide dismutase (SOD) activity increased and malondialdehyde (MDA) levels decreased significantly (P<0.05) in the intestine, hepatopancreas, plasma and muscles. The plasma complement-3 (C3) and complement-4 (C4) levels were significantly (P<0.05) improved at 5.0 g · kg−1 level and decreased when over 7.5 g · kg−1. The plasma lysozyme (LSZ) activity increased significantly (P<0.05) at 7.5, 10.0, or 15.0 g · kg−1 level. In summary, the results showed that Aln-Gln improved growth performance, development and function of the intestine, the activity of the antioxidant defense system and the plasma non-specific immunity of the carps. The optimal Aln-Gln level was 8.24 g · kg−1 diet for WGR based on broken-line regression model analysis.