Dietary 25-hydroxyvitamin D improves intestinal health and microbiota of laying hens under high stocking density

The high stocking density is a major stress factor that adversely affects the health and performance of poultry. Therefore, the object of this study was conducted to explore whether dietary 25-hydroxyvitamin D (25-OH-D(3)) could improve gut health of laying hens reared under high stocking density. A 2 × 2 factorial design was used in this 16-week study, in which 800 45-week-old Lohmann laying hens were allocated into two levels of dietary 25-OH-D(3) levels (0 and 69 µg/kg) and two rates of stocking densities [506 (low density, LD) and 338 (high density, HD) cm(2)/hen]. Compared with the layers with LD, the layers with HD had lower crypt depth in duodenum (P((Density)) < 0.05), lower short chain fatty acid (propionic and butyric acid) contents in cecum (P((Density)) < 0.05), and lower mRNA expression of intestinal barrier associated protein (claudin-1, mucin-1 and mucin-2). Exposed layer to HD also led to lower intestinal antioxidative capacity [superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), and higher malondialdehyde (MDA) content] in small intestine (P((Density)) < 0.05), lower bacterial abundance of Bacteroidetes (phylum), Spirochaetes (phylum) and Bacteroides (genus; P((Density)) < 0.05), higher bacterial enrichment of Lactobacillaceae (genus) and Firmicutes/Bacteroidetes ratio (P((Density)) < 0.05) in cecum. Dietary 25-OH-D(3) increased the villus height in duodenum and jejunum (P((25-OH-D3)) < 0.05), decreased Chao 1 and ACE indexes in cecum (P((25-OH-D3)) < 0.05), and it also up-regulated the mRNA expression of claudin-1, mucin-1 and mucin-2 (P((25-OH-D3)) < 0.05). Layers treated with 25-OH-D(3) led to an enhanced antioxidative enzyme activity of CAT (P((25-OH-D3)) < 0.05). Additionally, the effect of 25-OH-D(3) reversed the effect of HD on T-AOC and MDA content (P((Interaction)) < 0.05). In HD layers, 25-OH-D(3) administration decreased the enrichment of Bacteroidetes (phylum), increased Firmicutes (phylum), and Firmicutes/Bacteroidetes ratio (P((Interaction)) < 0.05). These results suggest that supplementing 25-OH-D(3) in diets may elevate gut health through the improvement of intestinal barrier function, antioxidant capacity and cecal microbiota composition in laying hens with high stocking density.