Abstract
This study aimed to investigate the benefit of dietary cecropin AD (CAD) on the intestinal health of turbot (Scophthalmus maximus) fed diets with a high level of soybean meal. A 12-week feeding trial was conducted with four isonitrogenous and isolipidic diets: a fishmeal-based diet (FM), a diet replacing 40% fish meal protein of FM diet with soybean meal protein (SBM), and the SBM diet supplemented with 0.5 g/kg (C1) and 1.0 g/kg (C2) CAD, respectively. The results of histology of distal intestine (DI) showed that turbots fed the SBM diet exhibited distinct symptoms of enteritis. However, fish fed diets with CAD supplementation kept the normal appearance of the DI which was similar to that in FM group. Compared with the SBM group, diet with CAD supplementation significantly decreased the gene expression of intestinal pro-inflammatory cytokines tumor necrosis factor-α (tnf-α), interleukin-1β (il-1β), interferon-gamma (ifn-γ), and nuclear factor-kappa B p65 (nf-κb p65), while up-regulated the gene expression of intestinal tight junction proteins claudin-3, claudin-4, occludin, and zonula occludens-1 (zo-1). Besides, diet C1 shaped the intestinal microbiota profile toward an anti-inflammatory phenotype represented by the increased abundance of Blutia, Firmicutes/Bacteroides ratio, and decreased Prevotellaceae. In conclusion, dietary CAD could positively modulate the intestinal health of turbot from the impairment induced by soybean meal, which expands its application to help fish better adapt to the increasing plant protein level in aquafeed.
Highlights
Soybean meal has been widely used in aquafeed to solve the contradiction between the soaring requirement and the lacking supply of fishmeal
The present study showed that dietary cecropin AD (CAD) markedly alleviated the symptom of the soybean meal-induced enteritis (SBMIE) in turbot, which was evidenced by the decreased eosinophilic granulocytes count in lamina propria and the reduced gene expression of pro-inflammatory cytokines
In line with our study, intake of porcine β-Defensin 2 attenuated the DSS-induced colitis by inhibiting the production of inflammatory mediators and preserving the integrity of colon in mice (Han et al, 2015), and Cathelicidin-WA was capable of attenuating intestinal inflammation and diarrhea in weaned diarrheal piglets (Yi et al, 2016)
Summary
Soybean meal has been widely used in aquafeed to solve the contradiction between the soaring requirement and the lacking supply of fishmeal. Given that intestinal microbial composition and barrier function can be effectively modified by dietary ingredients, and their significance in maintenance of intestinal homeostasis (Clements et al, 2014; Li et al, 2017; Zhou et al, 2018), many nutritional strategies such as functional amino acid/protein, probiotics, prebiotics, and organic acid have been exploited to relief fish SBMIE (Sealey et al, 2009; Refstie et al, 2010; Ulloa et al, 2016; Chen et al, 2018b; Liu et al, 2018; Zhao et al, 2019)
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