The current study was to investigate the modulatory effects of total dietary fiber (TDF) levels on cecal morphology and the response of microbiota to maintain gut health for duck growth. A total of 192 14-day-old male white Pekin ducks were randomly allocated to three dietary groups and fed diets, containing 12.4, 14.7, and 16.2% TDF, respectively, until 35 days under the quantitative feed intake. Each dietary group consisted of eight replicate cages of eight birds. The results revealed that 14.7 and 16.2% TDF groups significantly promoted growth performance and improved villus height, the ratio of villus to crypt, muscle layer thickness, and goblet cells per villus of cecum in ducks. qPCR results showed that the transcriptional expression of Claudin-1, Muc2, IGF-1, and SLC16A1 was significantly upregulated in cecum in 14.7 and 16.2% TDF groups. Meanwhile, the concentration of IGF-1 in circulating was significantly increased in 14.7 and 16.2% TDF groups while that of DAO was significantly decreased in 16.2% TDF group. Furthermore, the concentrations of butyrate, isobutyrate, valerate, and isovalerate in cecum were conspicuously improved in 14.7 and 16.2% TDF groups while that of propionate was significantly decreased. In addition, the concentrations of butyrate, isobutyrate, valerate, and isovalerate in cecum presented negative correlations with the concentration of DAO in circulating. 16S rRNA gene sequencing results showed that the 14.7% TDF group importantly elevated the microbial richness. Simultaneously, butyrate-producing bacteria like the family Lachnospiraceae, Oscillospiraceae, and Erysipelatoclostridiaceae were enriched as biomarkers in the 16.2% TDF group. Correlation network analysis revealed that the associations between specific bacteria and short-chain fatty acids (SCFAs) induced by different TDF levels, and the correlations among bacteria were also witnessed. For example, the genus Monoglobus and CHKCI002 showed a positive correlation with butyrate, and there was a positively coexistent association between Monoglobus and CHKCI002. In summary, these data revealed that increasing the TDF level could enhance the cecal morphology and drive cecal species-specific of SCFAs in ducks.

Riboflavin is an essential micronutrient and a precursor of flavin mononucleotide and flavin adenine dinucleotide for maintaining cell homeostasis. Riboflavin deficiency (RD) induces cell apoptosis. Endoplasmic reticulum (ER) stress is considered to induce apoptosis, and C/EBP homologous protein (CHOP) is a key pathway involved in this process. However, whether RD-induced apoptosis is mediated by ER stress and the CHOP pathway remains unclear and needs further investigation. Therefore, the current study presents the effect of RD on ER stress and apoptosis in the human hepatoma cell line (HepG2). Firstly, cells were cultured in a RD medium (4.55 nM riboflavin) and a control (CON) medium (1005 nM riboflavin). We conducted an observation of cell microstructure characterization and determining apoptosis. Subsequently, 4-phenyl butyric acid (4-PBA), an ER stress inhibitor, was used in HepG2 cells to investigate the role of ER stress in RD-induced apoptosis. Finally, CHOP siRNA was transfected into HepG2 cells to validate whether RD triggered ER stress-mediated apoptosis by the CHOP pathway. The results show that RD inhibited cell proliferation and caused ER stress, as well as increased the expression of ER stress markers (CHOP, 78 kDa glucose-regulated protein, activating transcription factor 6) (p < 0.05). Furthermore, RD increased the cell apoptosis rate, enhanced the expression of proapoptotic markers (B-cell lymphoma 2-associated X, Caspase 3), and decreased the expression of the antiapoptotic marker (B-cell lymphoma 2) (p < 0.05). The 4-PBA treatment and CHOP knockdown markedly alleviated RD-induced cell apoptosis. These results demonstrate that RD induces cell apoptosis by triggering ER stress and the CHOP pathway.

The current study was to investigate the effects of total dietary fiber (TDF) on growth performance, cecal structure, cecal microbial community, and short-chain fatty acids (SCFAs) profiles in the cecum of growing White Pekin ducks. A total of 108 male Pekin ducks of 14-days-old were randomly allocated and fed diets containing 12.4, 14.7, and 16.2% TDF for 35 days. Each dietary treatment consisted of six replicates with six birds each. The results showed that 14.7 and 16.2% TDF treatments promoted growth performance relative to 12.4% TDF treatments (P < 0.05). A total of 14.7 and 16.2% TDF treatments significantly elevated villus height, the ratio of villus height to crypt depth and muscle layer thickness of cecum, and lowered crypt depth compared with 12.4% TDF treatment (P < 0.05). Simultaneously, 14.7 and 16.2% TDF treatments up-regulated Claudin-1 mRNA expression of barrier genes in the cecum compared with 12.4% TDF (P < 0.05). Butyrate-producing bacteria like Oscillopiraceae affiliating to the phyla Firmicutes were observed as a biomarker in the 16.2% TDF. Higher concentration of butyrate in the cecum was obtained in the 14.7% TDF compared with 12.4 and 16.2% TDF (P < 0.05). The concentrations of isobutyrate, valerate, and isovalerate in the cecum were significantly increased in the 16.2% TDF compared with 12.4 and 14.7% TDF (P < 0.05). Meanwhile, the abundance of genus UCG-005 and Enterococcus was positive correlations with isobutyrate and valerate (P < 0.05). However, the concentration of propionate in the cecum significantly decreased in 14.7 and 16.2% TDF treatments relative to 12.4% TDF treatments (P < 0.05). In summary, increasing TDF levels improved growth performance, cecal histomorphology, and barrier function of meat ducks and it might be mediated by the changes of microbiota communities, especially bloom of SCFAs-producing bacteria, which facilitated the interaction between intestinal mucosa and microbiota.

• Dietary riboflavin supplementation improves breast meat quality of ducks. • Dietary riboflavin supplementation increases muscle n3-PUFA and PG contents. • Dietary riboflavin supplementation increases two odorants contents of muscle. • Dietary riboflavin supplementation enhances muscle antioxidant capacity. • Dietary riboflavin supplementation activates mitochondrial aerobic respiration.

Background: Although methionine (Met), the first-limiting dietary amino acid, has crucial roles in growth and regulation of lipid metabolism in ducks, mechanisms underlying are not well understood. Therefore, the objective was to use dietary Met deficiency to investigate the involvement of Met in lipid metabolism and fat accumulation of Pekin ducks. Methods: A total of 150 male Pekin ducks (15-d-old, 558.5 ± 4.4 g) were allocated into 5 groups (6 replicates with 5 birds each) and fed corn and soybean meal-based diets containing 0.28%, 0.35%, 0.43%, 0.50%, and 0.58% Met, respectively, for 4 weeks. Met-deficient (Met-D, 0.28% Met) and Met-adequate (Met-A, 0.43% Met) groups were selected for subsequent molecular studies. Serum, liver, and abdominal fat samples were collected to assess the genes and proteins involved in lipid metabolism of Pekin ducks and hepatocytes were cultured in vivo for verification. Results: Dietary Met deficiency caused growth depression and excess fat deposition that were ameliorated by feeding diets with adequate Met. Serum triglyceride and non-esterified fatty acid concentrations increased (P < 0.05), whereas serum concentrations of total cholesterol, low density lipoprotein cholesterol, total protein, and albumin decreased (P < 0.05) in Met-D ducks compared to those in Met-A ducks. Based on hepatic proteomics analyses, dietary Met deficiency suppressed expression of key proteins related to fatty acid transport, fatty acid oxidation, tricarboxylic acid cycle, glycolysis/gluconeogenesis, ketogenesis, and electron transport chain; selected key proteins had similar expression patterns verified by qRT-PCR and Western blotting, which indicated these processes were likely impaired. In vitro verification with hepatocyte models confirmed albumin expression was diminished by Met deficiency. Additionally, in abdominal fat, dietary Met deficiency increased adipocyte diameter and area (P < 0.05), and down-regulated (P < 0.05) of lipolytic genes and proteins, suggesting Met deficiency may suppress lipolysis in adipocyte. Conclusion: Taken together, these data demonstrated that dietary Met deficiency in Pekin ducks resulted in stunted growth and excess fat deposition, which may be related to suppression of fatty acids transportation and hepatic catabolism.

Background: As a major economic trait in poultry, egg production efficiency attracts widespread interest in breeding and production. However, limited information is available about the underlying genetic architecture of egg production traits in ducks. In this paper, we analyzed six egg production-related traits in 352 F ₂ ducks derived from reciprocal crosses between mallard and Pekin ducks. Results: Feed conversation ratio (FCR) was positively correlated with feed intake but negatively correlated with egg-related traits, including egg weight and egg production, both phenotypically and genetically. Estimates of pedigree-based heritability were higher than 0.2 for all traits investigated, except hip-width. Based on whole-genome sequencing data, we conducted genome-wide association studies to identify genomic regions associated with these traits. In total, 11 genomic regions were associated with FCR. No genomic regions were identified as significantly associated with hip-width, total feed intake, average daily feed intake, and total egg production. Analysis of selective sweeps between mallard and Pekin ducks confirmed three of these genomic regions on chromosomes 13, 3 and 6. Within these three regions, variants in candidate genes that were in linkage disequilibrium with the GWAS leader single nucleotide polymorphisms (SNPs) (Chr13:2,196,728, P = 7.05 × 10 ^–14 ; Chr3:76,991,524, P = 1.06 × 10 ^–12 ; Chr6:20,356,803, P = 1.14 × 10 ^–10 ) were detected. Thus, we identified 31 potential candidate genes associated with FCR, among which the strongest candidates are those that are highly expressed in tissues involved in reproduction and nervous system functions of ducks: CNTN4 , CRBR , GPR63 , KLHL32 , FHL5 , TRNT1 , MANEA , NDUFAF4 , and SCD . Conclusions: For the first time, we report the identification of genomic regions that are associated with FCR in ducks and our results illustrate the genomic changes that occurred during their domestication and are involved in egg production efficiency.