 In the diet, there are two forms of vitamin D – cholecalciferol (vitamin D3) from mainly animal sources, and ergocalciferol (vitamin D2) from plant, especially fungi sources.Although both forms have been shown to raise serum calcidiol levels, there is evidence that cholecalciferol has a greater effect on raising blood calcidiol than ergocalciferol.There is also evidence that vitamin D2 is less effective functionally than Vitamin D3 in humans and especially in cats, although similar studies have not been replicated in dogs.