Effects Of Dietary Folic Acid On Growth Performance And Intestinal Immunity Of Young Grass Carp (Ctenopharyngodon Idella) And The Mechanism Studies

To investigate the effects of dietary folic acid on fish growth performance, immunity, tight junctions and antioxidant capacity, as well as the potential mechanism, young grass carp (Ctenopharyngodon idelld) (267.69 ± 0.87 g) were fed diets containing graded levels of folic acid at 0.10 (basal diet),0.47,1.03,1.48,1.88 and 3.12 mg/kg diet for 8 weeks.Data showed that percent weight gain (PWG), specific growth rate, feed intake and feed efficiency were increased with folic acid up to optimum level (P< 0.05). Optimum folic acid increased intestinal trypsin, chymotrypsin, lipase, amylase, alkaline phosphatase, Na+/K+-ATPase, γ-glutamyl transpeptidase and creatine kinase (CK) activities (P< 0.05). Furthermore, optimum folic acid up-regulated intestinal CK and Na+/K+-ATPase alpha subunit isoform 1 mRNA levels (P< 0.05). However, folic acid had no effect on Na+/K+-ATPase alpha subunit isoform 8 mRNA levels in grass carp intestine (P> 0.05). Moreover, optimum folic acid up-regulated target of rapamycin (TOR) and S6 kinase 1 mRNA levels, and down-regulated eIF4E-binding protein mRNA levels in fish intestine (P < 0.05). Optimum folic acid increased acid phosphatase, lysozgme and complement C3 in the intestine of young grass carp (P< 0.05). Furthermore, optimum folic acid down-regulated interleukin 1β, interleukin 8, tumor necrosis factor α, nuclear factor κB p65, IκB kinase α(IKK-α), KK-β and IKK-γ mRNA levels and up-regulated interleukin 10, transforming growth factor β and inhibitor of κB mRNA levels in the intestine of young grass carp (P< 0.05). Our study also presented that moderate folic acid up-regulated occludin, ZO-1 and claudin-b mRNA levels in the intestine of grass carp (P< 0.05). Furthermore, optimal folic acid up-regulated claudin-15, MLCK and p38 MAPK mRNA levels in the intestine of grass carp (P< 0.05). Data from this study showed that ROS, MDA and PC contents were decreased by moderate folic acid in whole intestine (P< 0.05). In addition, the increase of Cu/ZnSOD, CAT, GPx, GST and GR activities, and the decrease of MnSOD activity may be due to that optimal folic acid up-regulated Cu/ZnSOD, CAT, GPx, GST and GR mRNA levels, and down-regulated MnSOD mRNA level in intestine (P< 0.05). Furthermore, optimal folic acid up-regulated NF-E2-related factor 2 mRNA level, whereas down-regulated both Keapla and Keaplb mRNA levels in intestine (P< 0.05). Additionally, in this study, base on PWG, the requirement of young grass carp (267-747 g) for folic acid was 1.60 mg/kg diet.