Dietary vitamin D3 supplementation protects laying hens against lipopolysaccharide-induced immunological stress

The effects of vitamin D on the immune function of laying hens are not well understood. This study investigated the effects of vitamin D 3 (VD 3 ) on laying performance and immunological functions in laying hens under Escherichia coli lipopolysaccharide (LPS) challenge. In experiment one, 360 Jinghong-1 strain layers (32 weeks) were randomly divided into four groups with six replicates per group and 15 hens per replicate. Hens were fed a basal diet supplemented with different levels of VD 3 (0; 500; 1500; or 3000 IU VD 3 /kg of diet) for 10 weeks to determine laying performance, egg quality, and other parameters. In experiment two, 24 Jinghong laying hens (32 weeks) were fed basal diets with either 0 or 3000 IU VD 3 /kg of diet. After 10 weeks of feeding, six hens from each treatment were injected intravenously with 8 mg/kg of body weight of either LPS or saline. Blood and spleen samples were obtained for immune parameter analysis 4 h after injection. VD 3 deficiency reduced egg production and egg quality; in addition, feed intake and feed-to-egg ratio increased. No significant differences were observed in these parameters except eggshell strength between dietary VD 3 supplemental levels at 500; 1500; and 3000 IU VD 3 /kg of diet. VD 3 deficiency increased serum hormone (calcitonin, parathyroid hormone, estradiol, and progesterone) and cytokine (IL-6, IL-10) levels, the ratio of IFN-γ to IL-4, myeloperoxidase activity and total IgG content in the serum, and upregulated the blood CD3 + T cell population. Splenic retinoid X receptor (RXR), nuclear factor-κB (NF-κB), inducible nitric oxide synthase (iNOS), and polymeric immunoglobulin receptor (pIgR) gene mRNA levels were upregulated in VD 3 -deficienct hens. VD 3 deficiency significantly reduced serum Follicle stimulating hormone (FSH) and Luteinizing hormone (LH) concentrations and the number of CD4 + CD25 + T cells in the blood. These changes were completely normalized by VD 3 sufficiency. LPS reduced serum LH concentration, splenic lysozyme, and pIgR gene mRNA levels. LPS induced an increase in total serum IgM levels and the percentage of CD8 + T cells in the blood. The changes were completely reversed by VD 3 addition. VD 3 supplementation could protect laying hens not only from VD 3 deficiency but also from immunological stress.