Vitamin D deficiency in the chick embryo: effects on prehatching motility and on the growth and differentiation of bones, muscles, and parathyroid glands.

Vitamin D-deficient chicken embryos were obtained by feeding laying hens diets in which 3-7 micrograms calcitriol replaced the vitamin D3 supplement. A large proportion of the D-deficient embryos failed to complete the prehatching positional changes required to start pulmonary respiration. For this reason most of them became cyanotic and had subcutaneous edema and hemorrhages in the head and neck and died without hatching. Total as well as leg-bone and muscle weights were significantly lower in the deficient embryos than in the controls and these changes probably explain the inability of the embryos to complete the movements required to place the beak in contact with the air chamber and start pulmonary respiration. The histological study of the tibiae showed decreased mineralization with narrower trabeculae and enlarged osteoid seams; bone resorption at the inner surface was also significantly decreased. The ultrastructural study of parathyroid glands showed increased functional activity reflected by increased number and size of cisternae of rough endoplasmic reticulum. Injection of 10 ng calcitriol, 1 microgram 24,25-(OH)2D3, or 2 micrograms 25OHD3 to deficient embryos on the 14th day of incubation improved hatchability, bone and muscle weights, and both bone mineralization and resorption.