Condensed tannins decreased the growth performance and impaired intestinal immune function in on-growing grass carp (Ctenopharyngodon idella)

The present study investigated the effects of condensed tannins (CT) on intestinal immune function in on-growing grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp were fed six diets containing different levels of CT (0, 10 center dot 00, 20 center dot 00, 30 center dot 00, 40 center dot 00 and 50 center dot 00 g/kg diet) for 70 d and then challenged with Aeromonas hydrophila for 14 d. The results showed that, compared with the control group, dietary CT (1) induced intestinal histopathological lesions and aggravated enteritis; (2) decreased lysozyme and acid phosphatase activities, complement 3 (C3), C4 and IgM contents and down-regulated the Hepcidin, liver-expressed antimicrobial peptide (LEAP)-2A, LEAP-2B, Mucin2 and beta-defensin-1 mRNA levels in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) (P < 0 center dot 05); (3) down-regulated the mRNA levels of anti-inflammatory cytokines transforming growth factor (TGF)-beta 1, TGF-beta 2 (not in MI and DI), IL-4/13A (not IL-4/13B), IL-10 and IL-11 partly correlated with target of rapamycin (TOR) signalling; and (4) up-regulated the mRNA levels of pro-inflammatory cytokines interferon-gamma 2, IL-1 beta, IL-6, IL-8 (not in PI), IL-12p35, IL-12p40, IL-15 and IL-17D partly related to NF-kappa B signalling in the intestine of on-growing grass carp. Overall, the results indicated that CT could impair the intestinal immune function, and its potential regulation mechanisms were partly associated with the TOR and NF-kappa B signalling pathways. Finally, based on the percentage weight gain and enteritis morbidity, the maximum allowable levels of CT for on-growing grass carp (232 center dot 22-890 center dot 11 g) were estimated to be 18 center dot 6 and 17 center dot 4 g/kg diet, respectively.