Importance of vitamin D for the regulation of calcium and phosphate metabolism in horses

The basic regulatory mechanisms of the calcium homeostatic system as they are mediated by calcitriol, PTH and calcitonin appear to be very similar among different species, One noteworthy exeption from this widespread principle, however, has been found recently by the demonstration of an active vitamin D-independent transport of calcium across the duodenum of newborn piglets. Own investigations with ponys and horses tend to show that the regulation of calcium and phosphate metabolism of horses also markedly differs from that of most other mammalian species. This conclusion is reached from the following observations.