Enhancing the ability of fish to consume a high-carbohydrate diet (HCD) is a key focus of aquaculture research. The propolis extract, caffeic acid phenethyl ester (CAPE) has anti-inflammatory, hepatoprotective, and glycolytic-promoting properties, but its potential to mitigate metabolic disorders in fish fed a HCD remains uncertain. This study investigated the effects of CAPE on the adaptability and utilization of a HCD in the herbivorous grass carp (Ctenopharyngodon idellus), focusing on growth performance, tissue and organ health, and nutrient metabolism. A total of 270 grass carp with an initial body weight of 12.69 ± 0.05 g were divided into five groups (Control, HCD, HCD + C200 [200 mg/kg CAPE], HCD + C500 [500 mg/kg CAPE], and HCD + C800 [800 mg/kg CAPE], respectively) with three replicates per group and fed for 8 weeks. Compared with Control group, the HCD reduced the final body weight, weight gain rate, specific growth rate, protein deposition rate, and crude protein in whole body and muscle (P < 0.05), and increased the feed conversion ratio, intraperitoneal fat index, and hepatosomatic index of grass carp (P < 0.05), whereas the addition of CAPE reduced these adverse effects (P < 0.05). Peroxisome proliferator-activated receptor γ (PPARγ) was activated by CAPE in adipose tissue (P < 0.05), but not in the hepatopancreas or muscle. These changes resulted in adipocyte hyperplasia (a smaller and more uniform distribution of adipocytes) and decreased immune cell penetration and inflammation. CAPE promoted the lipolysis and fatty acid β-oxidation in the adipose tissue, hepatopancreas, and muscle. CAPE improved glucose uptake and utilization-related gene expression in the hepatopancreas and muscle, alleviated hepatic steatosis, and promoted mammalian target of rapamycin (mtor) gene expression in muscle for grass carp on the HCD (P = 0.034). The addition of CAPE to the HCD inhibited inflammatory response in the adipose tissue, hepatopancreas, and muscle, and reduced the levels of alanine aminotransferase, aspartate aminotransferase, glucose, lactic dehydrogenase, low-density lipoprotein cholesterol, and triglycerides in the serum (P < 0.05). In summary, CAPE altered the pattern of adipose tissue expansion by promoting adipocyte hyperplasia, thereby promoting glucose and lipid metabolism, and ameliorated the adverse effects of a HCD on inflammation and growth performance in grass carp.

Dietary sanguinarine (SAN) can enhance the growth performance of poultry and livestock, but the regulatory mechanism of the SAN monomer on intestinal homeostasis and how it promotes growth performance has not yet been clarified. In this study, 200 chickens were divided into four groups and fed different doses of SAN (0, 0.225, 0.75, 2.25 mg/kg) for transcriptome and microbiota analysis. The data showed that different doses of SAN supplementation increased the feed conversion rate (FCR) of 22 to 42 d old and 1 to 42 d old broilers (P < 0.01), and 0.225 mg/kg SAN reduced the contents of alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine (CREA) and blood urea nitrogen (BUN) in serum (P < 0.01). Dietary SAN increased the villus height and the villus height/crypt depth (V/C) ratio in the ileum (P < 0.01). The levels of tight junction proteins (zonula occludens-1, occludin and claudin-1) were up-regulated in the ileum and cecum (P < 0.01) and the levels of immunoglobulin (Ig) A, IgM, IgG, interleukin (IL)-4, IL-10 and interferon (IFN)-γ were up-regulated in the serum and ileum (P < 0.01). RNA-seq analysis revealed 385 differentially expressed genes (DEGs) (|log2 fold change| ≥ 1, FDR < 0.05) between the SAN group and CON group. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed 15 pathways mostly associated with the immune system. Additionally, the reverse transcription-PCR results showed that the relative mRNA expression of β-defensin and mucin 2 were up-regulated (P < 0.01) and Toll-like receptor (TLR2 and TLR4) mRNA expression were down-regulated by SAN (P < 0.01), which was consistent with the transcriptomic analysis. Western blot analysis also showed that SAN reduced the expression of inflammatory proteins such as TLR4, nuclear factor-kappa B and IL-1β in the ileum (P < 0.01). In addition, at the genus level, SAN significantly increased the relative abundance of bacteria (Bacteroides, unclassified_f__Lachnospiraceae, Lactobacillus and Romboutsia) involved in acetate and butyrate production in the cecum, which are associated with enhanced intestinal immune function and maintaining intestinal health. In conclusion, SAN ameliorates the growth performance of broilers, enhances intestinal immune function, regulates the structure of microbiota and maintains intestinal health.