Heat Stress Induces Metabolic and Physiological Imbalance in Laying Hens, Accompanied by Hepatic Transcriptomic, Cecal Microbial, and Metabolomic Alterations

Heat stress is a major constraint to productivity and physiological homeostasis in laying hens. This study investigated integrated responses to acute heat stress using a multi-omics approach, including performance traits, serum biochemical parameters, histology, hepatic transcriptomics, cecal metagenomics, and metabolomics. Acute heat stress impaired productive performance, as reflected by changes in egg production and reduced eggshell strength, and induced systemic physiological disturbances, including increased stress- and injury-related blood indicators and disrupted metabolic and electrolyte balance. Histological analysis confirmed liver and intestinal tissue damage. Hepatic transcriptomics revealed inflammatory activation and suppression of metabolic pathways, particularly those involved in lipid metabolism, energy production, and redox homeostasis. Cecal metagenomic and metabolomic analyses showed altered microbial composition and functional potential, along with disruptions in amino acid, lipid, and energy metabolism. Collectively, these findings suggest that acute heat stress is associated with coordinated inflammatory responses and metabolic reprogramming, together with liver and intestinal injury and gut microbiota-metabolite alterations. The study provides a framework for understanding early heat stress responses and highlights potential targets for nutritional and microbiota-based interventions in poultry production. Importantly, serum biochemical indicators such as D-lactic acid and aspartate aminotransferase may serve as potential early biomarkers for monitoring heat-stress-induced physiological disturbances.