Dietary selenium sources alleviate immune challenge induced by potentially through improving the host immune response and gut microbiota in laying hens.

The aim of this study was to evaluate the effects of different selenium (Se) sources on the immune responses and gut microbiota of laying hens challenged with (). A total of 240 45-week-old layers were randomly divided into eight groups with six replicates per group according to a 4 × 2 factorial design, including a blank diet without Se supplementation (CON group) and three diets with 0.3 mg/kg Se supplementation from sodium selenite (IS group), yeast Se (YS group), and selenium-enriched yeast culture (SYC group), respectively. After 8 weeks of feeding, half of them were orally challenged with 1.0 ml suspension of 10 colony-forming units per milliliter of daily for 3 days. The serum was collected on days 3, 7, and 14, and the cecum content was collected on day 14 after challenge. There was no significant difference in laying performance among the eight groups before challenge. The challenge significantly decreased the laying performance, egg quality, GSH-Px, IgG, and IgM and increased the ratio of feed and egg, malondialdehyde (MDA), -specific antibody (SA) titers, IL-6, IL-2, IL-1β, and INF-γ. However, SYC increased the level of GSH-Px and IgG and decreased IL-6, while YS decreased the level of IL-2 and IL-1β. What is more, Se supplementation decreased the SA titers to varying degrees and reduced the inflammatory cell infiltration in the lamina propria caused by infection. In addition, the challenge disrupted the intestinal flora balance by reducing the abundance of the genera , , and and increasing the genera and , while Se supplementation increased the gut microbial alpha diversity whether challenged or not. Under the challenge condition, the alteration of microbial composition by the administration of different Se sources mainly manifested as IS increased the relative abundance of the genera and , YS increased the relative abundance of the genera and , and SYC increased the genera and . The alteration of gut microbial composition had a close relationship with antioxidant or immune response. To summarize, different Se sources can improve the egg quality of layers challenged by that involves elevating the immunity level and regulating the intestinal microbiota.