Abstract
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: VD(3) supplementation could protect laying hens not only from VD(3) deficiency but also from immunological stress.