Dietary milk thistle meal supplementation modulates gut microbiota and improves performance and egg quality in late-phase laying hens.

The decline in production performance of late-phase laying hens is closely associated with gut microbiota dysbiosis. This study evaluated whether dietary milk thistle meal (MTM) could improve performance by modulating the gut microbiota. A total of 450 Jinghong 3.0 laying hens (55 weeks old) were randomly allocated to five dietary treatments: a basal diet or diets with 2.5, 5.0, 7.5, or 10.0% MTM, respectively. The experiment lasted 8 weeks. Overall, results indicated dose-dependent effects of MTM on hen performance. Specifically, both average egg weight and feed conversion ratio (FCR) showed significant linear and quadratic responses to MTM level (P < 0.05). Notably, during the trial, the MTM5.0 group exhibited the highest average egg weight among all groups and lower FCR than the MTM10.0 group (P < 0.05). Regarding egg quality, yolk color was significantly improved in groups receiving ≥ 5.0% MTM compared with that of the CON group (P < 0.05), while the Haugh unit was highest in the 5.0% MTM group (P < 0.05). Similarly, the apparent crude protein digestibility was also highest in the MTM5.0 group (P < 0.05). 16S rRNA sequencing of excreta samples revealed that MTM modulated specific microbial taxa in a dose-dependent manner, with the 5.0% inclusion level associated with the best performance. Specifically, the relative abundance of genus Turicibacter increased linearly with dietary MTM level (P < 0.05). Additionally, the relative abundance of the phylum Bacteroidota and genus Bacteroides showed significant quadratic trends (P < 0.05). Functional prediction (PICRUSt2) further revealed that MTM predominantly influenced amino acid, carbohydrate, and lipid metabolism pathways, with the most pronounced effects at the 2.5% dose. Collectively, dietary inclusion of 5.0% MTM improved production performance and egg quality in late-phase laying hens, potentially through maintenance of gut microbial homeostasis and enhanced nutrient utilization.