Wysong supplements and diets are formulated using the natural foods canines adapted to in the wild over eons of time. We do not agree that canine and feline diets and supplements should not contain vitamin D.
That opinion that vitamin D should not be in pet foods would deny the incredible results tens of thousands of animals have had on Wysong Diets for the past 30 years through multiple generations. That constitutes far better evidence than theories about vitamin D.
Additionally, if anything, pets are deficient in this vitamin due to the fact that conventional pet food processing and food storage can greatly deplete the natural vitamin D in the ingredients.
For true insight on pet foods and nutrition, we recommend you read "The Truth About Pet Foods" book, as well as the dozens of articles in the Learn Section of the Wysong website: Pet Health and Nutrition. We also recommend that you read the O-Mega D monograph which has more information about the benefits of supplemental vitamin D.