Effects of N-carbamylglutamate on growth, liver function, intestinal structure and intestinal flora of Micropterus salmoides

The gradient concentration of 0, 360, 720 and 1 800 mg/kg NCG were added to the essential diet respectively, to study the effects of N-carbamylglutamate (NCG) on the growth, intestinal structure and flora of Micropterus salmoides. Meanwhile, the initial weight of (170.0±5.0) g M. salmoides was fed for 10 weeks, which were labeled as T0 control group, T360 group, T720 group and T1800 group, respectively. The results showed that the feed coefficient (FCR) of 360 and 720 mg/kg group was significantly lower than that of 0 mg/kg control group (P<0.05), and the weight gain rate (WGR) of 360 and 720 mg/kg group was significantly higher than that of other groups (P<0.05) . There was no significant difference in specific growth rate (SGR), condition factor (CF), hepatosomatic index (HSI), and viscera weight index (VSI) (P>0.05). The results of the liver tissue sections and related enzyme activity indicators showed that the liver cells of M. salmoides in the NCG supplemented group were closely arranged, and the tissue necrosis or inflammatory cells were reduced. The activities of glutamic oxaloacetic transaminase (ALT), glutamic pyruvic transaminase (AST) and malondialdehyde (MDA) content in the NCG supplemented group were significantly lower than those in the control group (P<0.05). In contrast, the lysozyme (LZM) activity was significantly higher than that in the T0 control group (P<0.05). The results of intestinal tissue sections showed that the villus height (VH), villus width (VW) and intestinal muscle thickness (IMT) of the NCG group were significantly higher than those of the T0 control group (P<0.05). The results of gut microbiome analysis showed that the number of gut microbiota species significantly increased in the NCG addition group, with the T720 group having the most species. The abundance of Plesiomonas decreased significantly, while the abundance of Cetobacterium decreased significantly first and then increased with the addition of NCG. Using the feed coefficient and weight gain rate as indicators, the optimal amount of NCG added to the diet of M. salmoides was determined through line analysis as 345.87 and 916.67 mg/kg, respectively. In conclusion, NCG can improve the liver function and intestinal health of M. salmoides, optimize the intestinal flora structure, promote the growth of M. salmoides, and reduce the FCR. The research results have important reference significance for the green and healthy cultivation of M. salmoides.