Why does all rabbit food contain animal products?

I have a beloved friend. His name is Pippin. He is a bunny. I want to feed him the best rabbit food, as natural and healthy as possible. I do not want to feed him junk, especially not animal products. Rabbits are herbivores (just like me!), but all packaged rabbit pellets that I’ve seen have vitamin D3 in them. D3 is made from animal products, D2 is make from plants. I do not want to feed my rabbit an animal product. What do I do? Is there a vegetarian rabbit food out there somewhere? Help!