Betaine supplementations enhance the intestinal immunity of on-growing grass carp (Ctenopharyngodon idella): Partly related to TOR and NF-κB signaling pathways

This study aims to explore the effects of dietary betaine (BET) supplementations in low methionine (Met) diet on the growth performance and intestinal immune function of on-growing grass carp (Ctenopharyngodon idella). A total of 540 on-growing grass carp (210 +/- 0.68 g) were fed with a normal met diet and five diets containing graded levels of BET supplementations (0, 1.6, 3.2, 4.8 and 6.4 g kg(-1)) in low met diet for 60 days. Subsequently, a challenge WA was conducted by injection with Aeromonas hydrophila for 14 days. Results showed that, compared with BET0 group, appropriate BET supplementations (1) could enhance the abilities of fish against enteritis, intestinal lysozyme activities (LZ), acid phosphatase activities (ACP), complement 3 (C3) and C4 contents and IgM contents, and up-regulate the transcript abundances of liver-expressed antimicrobial peptide (LEAP)-2A, LEAP-2B, LEAP-1/hepcidin and 13-defensin-1 (P < .05); (2) could down-regulate intestinal pro-inflammatory cytokines TNF-alpha, IL-1 beta, IFN-gamma 2, IL-6 and IL-8 mRNA levels partly related to [IKK beta, gamma/I kappa B alpha/NF-kappa Bp65, c-Rel] signaling pathway; (3) could up-regulate intestinal anti-inflammatory cytokine transforming growth factor (TGF)-beta 1, IL-4/13A and IL-10 mRNA levels partly related to the target of rapamycin (TOR) [TOR/ (S6K1, 4E-BP1 and 4E-BP2)] signaling pathway. Furthermore, BET could spare part methionine (Met) and the actually comprehensive efficacy of BET relative to DL-met was estimated to be 113.14% for on-growing grass carp (body weight 210-776 g) based on percent weight gain (PWG). Finally, based on PWG and LZ, the appropriate BET supplementations for on-growing grass carp (body weight 210-776 g) were estimated to be 4.28 and 4.51 g kg(-1) diet, respectively. In general, dietary BET supplementations in low met diet boosted the growth performance and enhanced the immune function in the intestines of on-growing grass carp.