Identification of key genes and pathways in duck fatty liver syndrome using gene set enrichment analysis.

High-laying ducks are often fed high-energy, nutritious feeds to maintain high productivity, which predisposes them to lipid metabolism disorders and the development of fatty liver syndrome (FLS), which seriously affects production performance and has a substantial economic impact on the poultry industry. Therefore, it is necessary to elucidate the mechanisms underlying the development of fatty liver syndrome. In this study, seven Shan Partridge ducks, each with fatty liver syndrome and normal laying ducks, were selected, and Hematoxylin Eosin staining (HE staining), Masson staining, and transcriptome sequencing were performed on liver tissue. In addition to exploring key genes and pathways using conventional analysis methods, we constructed the first Kyoto Encyclopedia of Genes and Genomes (KEGG) database-based predefined gene set containing 12,764 pathways and 16,836 genes and further performed gene set enrichment analysis (GSEA) on the liver transcriptome data. Finally, key nodes and biological processes were identified via the protein-protein interaction (PPI) network. The results showed that the liver in the FL group exhibited steatosis and fibrosis, and a total of 3,663 genes with upregulated expression versus 2,296 downregulated genes were screened by conventional analysis. GSEA analysis and PPI network analysis revealed that the liver in the FL group exhibited disruption of the mitochondrial electron transport chain, leading to decreased oxidative phosphorylation and the secretion of excessive proinflammatory factors amid the continuous accumulation of lipids. Under continuous chronic inflammation, cell cycle arrest triggers apoptosis, while fibrosis becomes more severe, and procarcinogenic genes are activated, leading to the continuous development and deterioration of the liver. In conclusion, the predefined gene set constructed in this study can be used for GSEA, and the identified hub genes provide useful reference data and a solid foundation for the study of the genetic regulatory mechanism of fatty liver syndrome in ducks.

Dietary supplementation with 2-hydroxy-4-methyl(thio) butanoic acid and DL-methionine improves productive performance, egg quality and redox status of commercial laying ducks.

This experiment aimed to study the effects of supplemental methionine sources, 2-hydroxy-4 methyl(thio) butanoic acid (HMTBa) and DL-Methionine (DL-Met), on productive performance, egg quality, and redox status of laying ducks. A total of 792 healthy 25-wk-old Longyan laying ducks with similar body weights were randomly allotted to 11 treatment groups. Each treatment group had 6 replicates of 12 ducks. The trial lasted for 16 wk. Ducks were fed a basal deficient diet (Met: 0.24%; Met + Cys: 0.51%) or supplemented with DL-Met or HMTBa at 0.05%, 0.12%, 0.19%, 0.26%, and 0.33% of diet, respectively. Compared with the basal diet, supplementation with either DL-Met or HMTBa increased the average egg weight, egg mass, and decreased feed to egg ratio during the whole trial period (P < 0.05). Albumen weight and its ratio to total egg weight were increased, but yolk and shell ratio, albumen height, Haugh unit and shell breaking strength were decreased (P < 0.05). Dietary DL-Met or HMTBa supplementation increased taurine, methionine, leucine, tryptophan and arginine content, and decreased serine and lysine content in plasma (P < 0.05). The redox status of laying ducks was improved by enhancing the glutathione peroxidase and catalase activities, glutathione content and its ratio relative to glutathione (oxidized) content and decreasing malondialdehyde content and increasing mRNA expression of superoxide dismutase-1, glutathione peroxidase-1, hemeoxygenase-1 and nuclear factor-like 2 in liver and ileum with the supplementation of DL-Met or HMTBa (P < 0.05). Liver health status measured by average area proportion lipid droplet was improved with supplementation of DL-Met or HMTBa (P < 0.05). Villus height and villus height to crypt depth ratio in the ileum and the ileal gene expression of tight junction protein and occludin were increased with DL-Met or HMTBa supplementation (P < 0.05). Taken together, these results suggested that the efficacy of dietary supplementation of HMTBa was similar to DL-Met, and it ranged from 98% to 100% for productive performance and egg albumen ratio in laying ducks (25 to 41 wk).

Age-related changes in eggshell physical properties, ultrastructure, calcium metabolism-related serum indices, and gene expression in eggshell gland during eggshell formation in commercial laying ducks.

This study evaluated the changes in eggshell mechanical properties, ultrastructure, calcium metabolism-related serum indices, and gene expression in eggshell gland during eggshell formation between laying ducks in the peak (young duck) and late phase (aged duck) of production. A total of 84 healthy young (31 wk of age) and 84 healthy aged (65 wk of age) Longyan laying ducks were each divided into 6 replicates of 14 birds, and caged individually. All the ducks were fed in one house with the same corn-soybean meal-based diet for 5 wk. The eggshell mechanical properties (shell proportion, thickness, breaking strength, and fracture toughness) and chemical components (matrix proteins, calcium, phosphorus, and magnesium) decreased in aged laying ducks (P < 0.05). Shell structural indices: total thickness, effective thickness and its proportion decreased, whereas mammillary knob width and its proportion increased (P < 0.05). The regulation values of early fusion, cuffing, caps, and total score of mammillary knobs were higher in aged laying ducks relative to the young ducks (P < 0.05). During the initial, growth and terminal stages of eggshell formation, shell thickness and breaking strength (terminal), shell weight, and its proportion (terminal) decreased in aged laying ducks (P < 0.05). Ultrastructural changes during shell formation indicated that the mammillary-knob density and effective thickness decreased (P < 0.05). Decreases occurred in serum content of phosphorus (growth), and estradiol and calcium contents (terminal) (P < 0.05). Relative expression of Ca2+ transporter and HCO3- exchanger, and matrix proteins genes decreased in aged laying ducks (P < 0.05) at all stages of eggshell formation. Collectively, the decreased incidence of early fusion and caps, increased thickness and width of mammillary knobs, and decreased effective thickness are the crucial differences leading to the compromised mechanical properties of eggshell in the late laying period. A disturbed regulation of calcium metabolism and uterine expression of ion transporters, especially for HCO3- exchange of aged laying ducks likely contribute to age-induced ultrastructural deterioration of the eggshell.

Dietary zinc supplementation affects eggshell quality and ultrastructure in commercial laying ducks by influencing calcium metabolism.

This study evaluated dietary Zn supplementation on productive performance, eggshell quality and ultrastructure, and calcium metabolism during eggshell formation in laying ducks. A total of 360 Longyan laying ducks (45-wk) were randomly divided into 5 treatment groups with 6 replicates of 12 birds each and fed for 20 wk. The 6 treatments fed the basal diet supplemented with 0 (control), 20, 40, 80, or 160 mg Zn/kg (ZnSO4·H2O). Dietary supplemental level at 80 mg/kg increased egg production (4.3%) and mass (5.7%), and decreased FCR (2.9%) compared to the basal diet, and these indices increased quadratically with increasing Zn supplemental levels (P < 0.05). The shell breaking strength (15.8%) and fracture toughness (10.6%) were higher with the supplementation of Zn at 80 mg/kg than the basal diet, and increased quadratically with Zn supplementation (P < 0.05). Dietary supplementation of Zn at 80 mg/kg improved shell ultrastructure by increasing total (9.0%) and effective thickness (14.2%) and decreasing mammillary thickness (12.0%), and their responses were quadratic with increasing Zn levels (P < 0.05). The supplementation of Zn affected the calcium contents in plasma, tibias and ulna, ulna phosphorus content, and linear and quadratic effects were observed, and higher values were observed with 160 mg/kg Zn supplementation than control (P < 0.05). The supplemental Zn level at 80 mg/kg increased shell effective thickness in growth stage (P < 0.05), and shell calcium and phosphorus content in initial and growth stages (P < 0.05). Dietary Zn supplementation did not affect the gene expression of Ca2+ transporters in the eggshell gland, but affected the expression of HCO3- exchanger in initial and growth stage (P < 0.05). Overall, dietary Zn supplementation could improve productive performance and shell quality in laying ducks at late phase of production, and calcium metabolism and deposition were modulated by Zn influencing HCO3- secretion and thus affecting shell ultrastructure and quality. A supplemental level of 80 mg/kg Zn in the diet with a basal content of 34.0 mg/kg was optimal, and higher level (160 mg/kg) decreased shell calcium deposition by depressing its metabolism.

Effects of dietary barley inclusion and glucanase supplementation on the production performance, egg quality and digestive functions in laying ducks.

This study evaluated the effects of barley inclusion and glucanase supplementation on the productive performance and digestive function in laying ducks. The experiment used a randomized design with a 5 × 2 factorial arrangement of 5 graded levels of barley (0%, 15%, 30%, 45% and 60%) with or without 1.5 g/kg ß-1,3-1,4-glucanase (15,000 U/kg). During the experimental period of 120 d, the weight and total number of eggs within each pen were recorded daily, and egg quality was determined every 4 wk. At the end of the experiment, 3 randomly selected ducks within each replicate were sacrificed, then duodenal digesta and jejunal mucosa was collected. Dietary inclusion of barley had no effects on egg production, daily egg mass or FCR, but supplementation with glucanase improved egg production and FCR (P < 0.01). Barley did not affect feed intake of laying ducks, but glucanase tended to increase feed intake (P = 0.09). Neither barley nor ß-glucanase had effects on the egg quality variables, except for yolk color score, which was decreased with increasing barley supplementation. Glucanase, but not barley, increased the activity of chymotrypsin and amylase in duodenal digesta. Barley inclusion affected the activity of alkaline phosphatase and maltase in jejunal mucosa (P < 0.05), but ß-glucanase had no effects on the activity of these brush border enzymes. Barley inclusion increased the glucan content in duodenal digesta, but supplementation of glucanase to barley-based diet reduced digesta glucan content and reduced total volatile fatty acids and increased the proportion of acetic acid in cecal contents. The results indicate that, without glucanase, the optimal dietary barley level in the diets of laying ducks is about 13% for maximal production performance; glucanase supplementation of the barley diets improved production performance, probably through enhancing digestive function.