I contacted Dr. Fuhrman right away and asked about the Pixie-Vites. You can visit the Disease Proof blog to read his response.
Here's a quote:
The reason why the Vitamin D in Pixie Vites is not vegan and made from wool (please note it is not made by killing animals) is because that form of D is twice as absorbable as the vegan type and many kids do not eat a whole Pixie Vite and only take a small portion of one. I did not want to short change some kid by not supplying them with adequate D, so I let that one non-vegan ingredient slip by (since it is made from a by product of wool manufacturing).