Dietary glycerol monolaurate mitigates heat stress-induced disruption of intestinal homeostasis and hepatic lipid metabolism in laying hens.

Heat stress (HS) disrupts intestinal homeostasis and hepatic lipid metabolism in poultry, yet effective interventions remain limited. We investigate the protective effects of dietary glycerol monolaurate (GML) supplementation in laying hens under HS conditions. In a 10-week trial, 504 Hy-Line Brown hens were assigned to four groups (control and GML at 65, 195, and 325 mg/kg) with six replicates per group. Hens receiving 325 mg/kg GML exhibited significantly higher egg production and egg weight (P < 0.05), alongside improved egg quality metrics, including increased shell strength and Haugh units by week 8 (P < 0.05). Histological analysis revealed that GML (325 mg/kg) improved duodenal and ileal villus height and duodenal villus-to-crypt ratios while reducing duodenal crypt depth (P < 0.05), thereby restoring gut barrier integrity. These findings were supported by reduced plasma D-lactate (D-LA) levels and upregulated expression of tight-junction proteins ZO-1 and Occludin in the ileum and jejunum (P < 0.05). In the liver, GML supplementation alleviated HS-induced steatosis, reducing lipid droplet accumulation (P < 0.05), plasma low-density lipoprotein cholesterol (LDL-C), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels, and hepatic triglyceride content, while elevating high density lipoprotein cholesterol (HDL-C). Integrated plasma metabolomics and hepatic transcriptomics identified 36 differential metabolites (enriched in sphingolipid metabolism) and 1,176 differentially expressed genes (enriched in PPAR signaling and Fatty acid degradation), with ACSL1 as a central regulatory gene. Key genes (ACSL1, CPT1 A) and metabolites correlated positively with production performance and gut-liver health, while SCD and Probucol showed negative associations. These findings indicate that GML supplementation enhances intestinal barrier function, promotes hepatic fatty acid β-oxidation, and reinforces sphingolipid metabolism, thereby mitigating HS-induced oxidative stress and lipid dysregulation. Our results identify 325 mg/kg GML as the optimal dosage, proposing a practical strategy to enhance poultry resilience during heat stress.