Rehmanniae Radix Powder Enhances Antioxidative Capacity, Immunity, and Gut Health in Late-Phase Laying Hens.

Physiological function is closely linked to production performance in laying hens, especially during the late laying phase. Rehmanniae Radix powder (RRP), derived from the root of Rehmannia glutinosa Libosch., exhibits diverse biological activities. We investigated the effects of RRP on immune function in late-phase laying hens. Antioxidant capacity, serum biochemical parameters, splenic immune function, and intestinal health were evaluated. Egg production rate in the RRP group increased by 1.39 percentage points compared with the control group, while average egg weight was not significantly different between groups. Dietary RRP supplementation elevated superoxide dismutase activity and serum albumin level. Splenic expression of immune-related factors, including J-chain, interleukin-2, and caspase-3, was upregulated to varying degrees following RRP supplementation. Helper-to-cytotoxic T-cell ratio also increased, indicating enhanced immune regulation. Intestinal tight junction protein expression was significantly upregulated in the RRP group. RRP also altered relative abundance of intestinal microbes at phylum and genus levels, decreasing Actinobacteria abundance and increasing Bacteroidota abundance. Similarly, relative abundance of Bacteroides and noank_f_norank_o_Clostridia_UG-014 was elevated. Biological function of the microbial community predictions showed that glycolysis/gluconeogenesis, alanine/aspartate/glutamate, fatty acid biosynthesis, and metabolism were upregulated, while that of the quorum-sensing pathway declined. RRP supplementation improved antioxidant status, splenic immune function, and intestinal health, thereby enhancing physiological conditions in laying hens during the late laying phase.