Mannan oligosaccharides improved growth performance and antioxidant capacity in the intestine of on-growing grass carp (Ctenopharyngodon idella)

This study evaluates the effects of dietary mannan oligosaccharides (MOS) supplementation on growth performance and antioxidant capacity, as well as investigates its related signalling molecule mechanism in the intestine of on-growing grass carp (Ctenopharyngodon idella). A total of 540 on-growing grass carp (215.85 ± 0.30 g) were fed six diets containing graded levels of MOS supplementation (0, 200, 400, 600, 800 and 1000 mg kg−1) for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila for 14 days. The results showed that (1) appropriate dietary MOS supplementation improved growth performance and enhanced disease resistance (2) appropriate dietary MOS supplementation relieved oxidative damage by decreasing the content of reactive oxygen species (ROS), and oxidative damage biomarker protein carbonyl (PC) and malondialdehyde (MDA). (3) appropriate dietary MOS supplementation enhanced antioxidant capacity by increasing enzyme activities [except manganese superoxide dismutase (MnSOD)] and corresponding gene expression (except MnSOD). (4) appropriate dietary MOS supplementation positively regulated antioxidant function related to MR/PKCδ/Nrf2/Keap1b (not Keap1a in the DI, not PKCα and PKCε in three intestinal segments) signalling pathway. In conclusion, the present study has demonstrated that dietary MOS supplementation could enhance fish intestine antioxidant capacity. Finally, based on the quadratic regression analysis for the percent weight gain (PWG), against enteritis morbidity, and the MDA, PC and ROS contents (in the DI) of on-growing grass carp, the MOS dosage was estimated to be 428.5, 499.1, 536.2, 561.7 and 550.9 mg kg−1 diet, respectively.