Abstract
In an experiment to produce hypervitaminosis A, twenty-two Holstein calves, 3 months of age and with a plasma vitamin A of 10 μg/100 ml or less, were fed vitamin A levels of 18, 54, 4000, 12,000 or 16,000 μg/lb of body weight per day for a 12-week period, except for the 16,000 μg group which was terminated in 8 weeks. The long bones and skulls were examined by X-rays and histologically.
The roentgenologic changes were a slowing of growth and remodeling processes in all calves on the 3 highest levels resulting in diminution of the overall size, thinning of the cortical bone and a marked decrease in the amount of spongious bone. Serial radiographs at weekly intervals of the radii of the calves on the highest level of vitamin A demonstrated changes as early as 2 weeks after administration of the vitamin supplement was begun.
The gross pathologic changes correlated well with the radiographic findings, except that failure of the internal bony plates of the frontal sinuses to form was not detected in the radiographs. The lack of bony separation of the brain from the frontal sinuses and the expansion of the cerebrum into these sinuses may explain the decreased cerebrospinal fluid pressure which accompanied the dilated cerebral ventricles.
Histologically, the essential change was retarded osteogenesis with poor differentiation of the mesenchymal cells into osteoblasts. As a result, the compacta was thin, osteoporotic and, at the 2 higher levels of vitamin A administration, contained large amounts of fibrous bone. As demonstrated in calves, the effect of excessive vitamin A on bone appears to be retardation of bone growth due to a defect in osteoid production resulting in osteoporosis.