Tonic immobility (TI) serves as an indicator of innate stress response recovery in poultry. Broilers with different TI phenotypes exhibit varying levels of aggressive behavior, which can significantly impact their welfare. However, the influences of TI phenotypes on broiler aggression remain largely unexplored. In this study, broiler chickens were stratified into two distinct phenotypic groups based on the TI duration: short TI (STI) and long TI (LTI). The impacts of TI phenotypes on broiler aggression were investigated by analyzing cecal intestinal morphology, cecal bacteria, plasma metabolites, and corticosterone levels. Compared to LTI broilers, STI broilers showed significantly reduced plasma corticosterone (CORT) levels (p < 0.05) and a decreased frequency of aggressive behaviors, including dominant and subdominant types (p < 0.01). Histological analysis revealed that STI broilers have an increased duodenal villus height and villus-height-to-crypt-depth ratio (p < 0.01), a decreased jejunal crypt depth with an increased villus-height-to-crypt-depth ratio (p < 0.01), and a reduced ileal crypt depth and villus height (p < 0.01) compared to LTI broilers. 16S rDNA sequencing and Linear discriminant analysis effect size (LefSe) identified differential cecal bacterial abundance, notably in the genus cc115 belonging to Firmicutes. Specific microbiota in LTI broilers exhibited significant positive correlations with aggressive behavior and plasma corticosterone, while those in STI broilers showed significant negative correlations. Untargeted plasma metabolomics revealed 21 downregulated and 17 upregulated metabolites between TI phenotypes. Correlation analysis showed that the genus cc115 and 10 plasma metabolites were positively correlated with aggressive behavior, whereas 8 metabolites were negatively correlated. LTI broilers have higher plasma corticosterone content and more intense aggressive behavior than STI broilers. The distinct behavioral and physiological profiles observed in broilers with different TI phenotypes are strongly correlated with their specific gut microbiota and differential plasma metabolite profiles. The identified gut microbial signatures serve as key biomarkers for regulating aggressive behavior in broilers, while the differential plasma metabolites represent potential early indicators for detecting stress and behavioral issues in poultry farming.

Iron is a trace element that is indispensable for the growth and development of animals. Excessive iron supplementation may lead to iron overload and elevated reactive oxygen species (ROS) production in animals, causing cellular damage. Nevertheless, the precise mechanism by which iron overload causes cell injury remains to be fully elucidated. In this study, 16 male SD rats aged 6 to 7 weeks were randomly assigned to either a control group (CON) or an iron overload group (IO). Rats in the iron overload group received 150 mg/kg iron dextran injections every three days for a duration of four weeks. The results indicated that iron treatment with iron dextran significantly increased the scores of steatosis (p < 0.05) and inflammation (p < 0.05) in the NAS score. The integrated transcriptomic and proteomic analysis suggests that HO-1 and Lnc286.2 are potentially significant in iron overload-induced liver injury in rats. In vitro experiments utilizing ferric ammonium citrate (FAC) were conducted to establish an iron overload model in rat liver-derived BRL-3A cells. The result found that FAC treatment can significantly increase the BRL-3A cell’s Fe2+ content (p < 0.05), ROS (p < 0.01), lipid ROS (p < 0.01) levels, and the expression of the HO-1 gene and protein (p < 0.01), aligning with proteomic and transcriptomic findings. HO-1 inhibition can significantly decrease BRL-3A cell vitality (p < 0.01) and promote ROS (p < 0.05) and lipid ROS (p < 0.01), thus aggravating FAC-induced BRL-3A cell iron overload damage. Using the agonist of HO-1 agonist cobalt protoporphyrin (CoPP) to induce HO-1 overexpression can significantly alleviate the decrease in FAC-induced BRL-3A cell viability (p < 0.01), ROS (p < 0.01), and lipid ROS (p < 0.01). In addition, siLnc286.2 treatment can increase HO-1 expression, alleviate the decline of FAC-induced BRL-3A cell activity, and increase lipid ROS (p < 0.05) content. In conclusion, the findings of this study suggest that by suppressing the expression of Lnc286.2, we can enhance the expression of HO-1, which in turn alleviates lipid peroxidation in cells and increases their antioxidant capacity, thereby exerting a protective effect against liver cell injury induced by iron overload.

Heat stress (HS) has emerged as a major environmental stressor, inducing oxidative stress, hepatic steatosis and impairing production performance and health in laying hens, with limited evidence-based nutritional interventions available. This study investigated the hepatoprotective effects of dietary silymarin (SIL) against chronic HS. In a 10-week trial, 252 43-week-old Hy-Line Brown hens were exposed to daily HS (32 ± 1℃, temperature-humidity index [THI] > 73) and fed either a basal diet or one supplemented with 100 mg/kg SIL. SIL significantly increased laying rate (P < 0.05) and improved albumen height, Haugh units, and shell strength by week 8 (P < 0.05). Histological analysis showed a 48% reduction in non-alcoholic fatty liver disease (NAFLD) activity score, with significantly decreased hepatic triglyceride content (P < 0.05); Oil Red O staining confirmed reduced lipid droplet accumulation. SIL restored redox balance by increasing plasma and hepatic total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px) (P < 0.05), increasing hepatic catalase (CAT) and glutathione (GSH) levels while decreasing malondialdehyde (MDA) (P < 0.05). Untargeted plasma metabolomics identified 11 key metabolites related to 2-oxoglutarate and purine metabolism, while hepatic transcriptomics revealed 835 differentially expressed genes primarily in the PPAR signaling and fatty acid biosynthesis pathways. SIL suppressed de novo lipogenesis via downregulation of ACACA and FASN, and enhanced β-oxidation through upregulation of CPT1A and ACSL1 (P < 0.05). Molecular docking and Western blotting confirmed strong SIL binding to these targets and corresponding protein changes. Correlation networks associated ACSL1 and CPT1A with improved performance and antioxidant indices, while FASN, ACACA, and xanthosine showed inverse relationships. These findings emphasize the potential of SIL as a sustainable animal nutrition antioxidant additive, which can alleviate HS induced lipid disorders in the liver of laying hens and provide insights for livestock applications.

Heat stress (HS) has emerged as a major environmental stressor, inducing oxidative stress and hepatic steatosis and impairing production performance and health in laying hens, with limited evidence-based nutritional interventions available. This study investigated the hepatoprotective effects of dietary silibinin (SIL) against chronic HS. In a 10-week trial, 252 43-week-old Hy-Line Brown hens were exposed to daily HS (32 ± 1 °C, temperature–humidity index [THI] > 73) and fed either a basal diet or one supplemented with 100 mg/kg SIL. SIL significantly increased laying rate (p < 0.05) and improved albumen height, Haugh units, and shell strength by week 8 (p < 0.05). Histological analysis showed a 48% reduction in non-alcoholic fatty liver disease (NAFLD) activity score, with significantly decreased hepatic triglyceride content (p < 0.05); Oil Red O staining confirmed reduced lipid droplet accumulation. SIL restored redox balance by increasing plasma, hepatic total superoxide dismutase (T-SOD), and glutathione peroxidase (GSH-Px) (p < 0.05), increasing hepatic catalase (CAT) and glutathione (GSH) levels while decreasing malondialdehyde (MDA) (p < 0.05). Untargeted plasma metabolomics identified 11 key metabolites related to 2-oxoglutarate and purine metabolism, while hepatic transcriptomics revealed 835 differentially expressed genes primarily in the PPAR signaling and fatty acid biosynthesis pathways. SIL suppressed de novo lipogenesis via downregulation of ACACA and FASN, and enhanced β-oxidation through upregulation of CPT1A and ACSL1 (p < 0.05). Molecular docking indicated favorable binding affinities between SIL and these targets, which was further supported by corresponding changes in protein expression via Western blotting. Correlation analysis revealed a consistent alignment between the upregulation of ACSL1/CPT1A and improvement in performance and antioxidant status, suggesting a coordinated metabolic shift. These findings emphasize the potential of SIL as a sustainable animal nutrition antioxidant additive, which can alleviate HS-induced lipid disorders in the liver of laying hens. Importantly, these hepatoprotective effects were demonstrated exclusively under chronic heat stress conditions; further studies incorporating a normothermic baseline are required to distinguish stress-specific mitigation from general metabolic stimulation.