Evaluation the effect of thiamin deficiency on intestinal immunity of young grass carp (Ctenopharyngodon idella)

• Thiamin deficiency impaired the intestinal immune response of young grass carp.
• Thiamin regulated the tight junction proteins mRNA levels of young grass carp.
• Thiamin deficiency decreased intestinal antioxidant capacity of young grass carp.
• Thiamin regulated the mRNA expression of NF-κB, TOR, MLCK and Nrf2.

Our study explored the effect of dietary thiamin on growth and immunity (intestine, head kidney, spleen and liver) of young grass carp (Ctenopharyngodon idella). Fish were fed diets containing six graded levels of thiamin at 0.12–2.04 mg/kg diet for 8 weeks. The percentage weight gain (PWG), feed intake and feed efficiency were lower in fish fed the 0.12 mg/kg diet. Thiamin deficiency decreased complement 3 content, lysozyme (LA) and acid phosphatase activities, mRNA levels of hepcidin and interleukin (IL) 10, elevated mRNA levels of interferon γ2, tumor necrosis factor α, IL-1β and IL-8 in intestine, head kidney, spleen and liver. The mRNA levels of inhibitor protein-κBα, target of rapamycin (TOR) and NF-E2-related factor 2 (Nrf2), the activities and mRNA levels of copper/zinc superoxide dismutase, manganese superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase were down-regulated, mRNA levels of myosin light-chain kinase (MLCK), IκB kinases (IKKβ and IKKγ), nuclear factor κB P65 (NF-κB P65) and Kelch-like-ECH-associated protein 1a (Keap1a) were up-regulated in the intestine of fish fed the thiamin-deficient diet. Additionally, thiamin deficiency decreased claudin b, c and 3, ZO-1 and occludin mRNA levels in each intestinal segment, increased claudin 12 and claudin 15a mRNA levels in distal intestine. In conclusion, thiamin deficiency decreased fish growth and immunity of intestine, head kidney, spleen and liver. The dietary thiamin requirement of young grass carp (242–742 g) based on intestinal LA activity or PWG were determined to be 1.15 or 0.90 mg/kg diet, respectively.