Vitamin D deficiency alters the immune responses of broiler chicks.

Three experiments were conducted to test the hypothesis that a vitamin D deficiency alters the immune responses of female broiler chicks. The control diet contained 800 IU of cholecalciferol (vitamin D3)/kg and the deficient diet was the same except without supplemental vitamin D3. The vitamin D deficiency status was established on the basis of a significantly lower blood ionized calcium or total serum calcium (75 to 85% of the control). Vitamin D-deficient chicks also had lower growth rate and bone ash. In Experiment 1 at 8 d of age, and Experiment 2 at 23 d of age, the cutaneous basophil hypersensitivity response as determined by the increase in interdigital skin thickness 20 h after a single injection of 100 microg phytohemagglutinin-P was significantly depressed in vitamin D-deficient chicks (62 to 64% of the control). Thymus weight, adjusted for body weight, was significantly lower in the vitamin D-deficient chicks at 24 d of age (61% of the control). Primary and secondary antibody responses against SRBC in vitamin D-deficient chicks were not different from the control. In Experiment 3, in 17-d-old chicks, vitamin D deficiency decreased the number of abdominal macrophages phagocytizing SRBC in vitro within 45 min from 14.7 to 10.1%. These results indicate that vitamin D deficiency depresses the cellular immune responses in young broiler chicks.