Dietary thyme essential oil supplementation improves production performance, egg quality, antioxidant status, and intestinal health in late-phase laying hens.

Thyme essential oil (TEO), a phytogenic feed additive extracted from Thymus vulgaris L., has been shown to enhance poultry performance; however, information regarding its effects in late-phase laying hens remains limited. This study evaluated the effects of dietary TEO supplementation on laying performance, antioxidant status, intestinal morphology, and cecal microbiota in late-phase Hy-Line Brown hens. A total of 160 hens were randomly assigned to four dietary treatments containing 0, 100, 300, or 500 mg/kg TEO and fed the experimental diets for 42 d. Dietary TEO supplementation significantly increased egg production compared with the control group (P < 0.05). Haugh unit values were higher in TEO-treated groups during days 22 to 42 (P < 0.05). Supplementation with 300 and 500 mg/kg TEO increased serum total antioxidant capacity (T-AOC) and the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), while decreasing malondialdehyde (MDA) concentrations (P < 0.05). Villus height and the villus height-to-crypt depth ratio in the jejunum and ileum were improved in TEO-fed hens (P < 0.05). Cecal microbiota analysis conducted in the control and TEO 300 mg/kg groups showed increased microbial richness and altered community composition following TEO supplementation, characterized by a higher relative abundance of Bacteroidota and a lower relative abundance of Bacillota. Collectively, these results indicate that dietary TEO supplementation improves laying performance and antioxidant status and modulates intestinal morphology and cecal microbial structure, suggesting its potential as a nutritional strategy to support health and productivity in aging laying hens.