Erucic acid impairs intestinal immune function of on-growing grass carp (Ctenopharyngodon idella)

Erucic acid (EA) mainly occurs in rapeseed meal as an anti-nutritional factor which can deteriorate animal growth performance. To our knowledge, the deteriorated animal growth performance is closely correlated with the impaired intestinal immune function. Thus, a 60-day feeding trial was carried out to explore the relationship of EA and the intestinal immune function of on-growing grass carp (Ctenopharyngodon idella). Fish (129.17 +/- 0.19 g) were distributed into 18 cages (length, width and height all equal to 1.4 m) at a stocking density of 15 individuals/m(3) and received 6 diets 4 times a day to apparent satiety for 60 days. The basal diet, to which different levels of EA were added to obtain 0.00 (control), 0.29, 0.60, 0.88, 1.21 and 1.50% EA, contained 28.73% crude protein and 6.43% crude lipid. At the end of the feeding trial, 24 fish of similar body weight from each group were used in a challenged test with Aeromonas hydrophila for 6 days and then collected to evaluate the effect of EA on morbidity of enteritis, intestinal immune parameters and intestinal inflammatory parameters. In fish intestine, our study found that EA: (1) reduced the activities of lysozyme (LZ) and acid phosphatase (ACP) and the contents of complement 3 (C3), C4 and immunoglobulin M (IgM); (2) decreased the transcript levels of liver-expressed antimicrobial peptide (LEAP)-2A, LEAP-2B, hepcidin, beta-defensin-1 and mucin2; (3) aggravated inflammatory response in relation to the increased transcript levels of pro-inflammatory cytokines involved in the activation of [I kappa B kinase beta, gamma (IKK gamma)/inhibitor of kappa B alpha (I kappa B alpha)/nuclear factor (NF)-kappa Bp65 and c-Rel] signalling pathway and to the decreased transcript levels of anti-inflammatory cytokines involved in the suppression of [target of rapamycin (TOR)/ribosomal protein S6 kinases 1 (S6K1) and eIF4E-binding proteins (4EBP)] signalling pathway. EA did not alter the transcript levels of interleukin (IL)-12p35, NF-kappa B p52 and IKKa in the intestine of on-growing grass carp. Finally, based on a straight broken-line model and using enteritis morbidity and the activities of LZ in proximal intestine (PI), mid intestine (MI) and distal intestine (DI) as response criterions, the maximum tolerance levels of EA for on-growing grass carp (129.17-471.18 g) were evaluated to be 0.53%, 0.36%, 0.44% and 0.45% diet, respectively.