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This study was conducted to determine the effects of 25-hydroxycholecalciferol (25-OH-D3) on performance, egg quality, tibia quality, and serum hormones concentration in laying hens reared under high stocking density. A total of 800 45-week-old Lohmann laying hens were randomly allotted into a 2 × 2 factorial design with 2 levels of dietary 25-OH-D3 levels (0 and 69 μg/kg) and 2 rates of stocking densities [506 (low density) and 338 (high density) cm2/hen]. Laying hens were monitored for 16 wk. High stocking density decreased laying rate, egg weight, and feed intake compared with low stocking density (P < 0.01) during 1 to 8 wk and 1 to 16 wk. Overall, high stocking density increased eggshell lightness value and decreased shell redness and yellowness value, strength, thickness, and relative weight compared with low stocking density (P < 0.05). Dietary supplementation with 25-OH-D3 reduced the value of the eggshell lightness and increased its yellowness and eggshells weight (P ≤ 0.05). The increase in eggshell thickness was more pronounced when 25-OH-D3 was supplemented to layers under high stocking density (interaction, P < 0.05). Layers under high stocking density had lower ash content and calcium content in the tibia than layers under low stocking density (P = 0.04); dietary 25-OH-D3 increased tibia strength compared with no addition (P = 0.05). Layers under high stocking density had higher serum concentrations of 25-OH-D3, corticosterone (CORT), lipopolysaccharide (LPS), and osteocalcin (OC; P < 0.05), lower content of parathyroid hormone (PTH) compared with layers under low stocking density (P < 0.01). Dietary 25-OH-D3 increased serum concentration of 25-OH-D3, carbonic anhydrase (CA), and calcitonin (CT) (P < 0.01) and reduced corticosterone, lipopolysaccharide and osteocalcin concentration (P ≤ 0.05). The increase effect in PTH was more pronounced when 25-OH-D3 was supplemented to layers under high stocking density (interaction, P = 0.05). Overall, the results gathered in this study indicate that high stocking density result in reducing production performance, shell color and quality, and tibia health, whereas dietary 25-OH-D3 was able to maintain tibia health and to mitigate the negative impact of high stocking density on productive performance.

ABSTRACT: 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-D3) 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-D3 levels (0 and 69 µg/kg) and two rates of stocking densities [506 (low density, LD) and 338 (high density, HD) cm2/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-D3 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-D3 led to an enhanced antioxidative enzyme activity of CAT (P(25-OH-D3) < 0.05). Additionally, the effect of 25-OH-D3 reversed the effect of HD on T-AOC and MDA content (P(Interaction) < 0.05). In HD layers, 25-OH-D3 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-D3 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.