Sally Fallon Morell replies:
I don’t know of any studies. Usually farmers give some alfalfa in the winter because it helps the cow produce more milk

You can get good and useful D3 from raw milk – but pasteurization destroys it. It is replaced, but I am unsure if D2 or D3 is used. This: https://www.westonaprice.org/health-topics/abcs-of-nutrition/vitamin-a-on-trial-does-vitamin-a-cause-osteoporosis/#appendix1
very good article, says the actual amount of vitamin D needed is pretty high; so you need sunlight, too. It points out, however, that without adequate vitamin A, it causes liver damage. Weston Price pointed out that sunlight alone wasn’t sufficient to ward off some conditions.

The real reason to prefer raw milk, is that pasteurization destroys too many other good nutrients. It destroys immunoglobulins which can confer immunity to the things cows are immune to. It destroys vitamin C in milk (yes, it’s supposed to be in there). Modern studies on milk associate its use with an increased risk of cancer. Price pointed out cancer was virtually unknown among indigenous, isolated communities drinking milk, which was certainly, at the time, raw. Price knew of about eight factors present in vitamin D, if memory serves.

Sally Fallon Morell replies: There will be vitamin D in whole milk from pastured cows, but better sources are butter, egg yolks, lard, poultry liver and cod liver oil. These should all be included in the diet of your children.