biochemistry - Diet of free-range herbivores

One key nutrient worth thinking about in the context of this question is vitamin B₁₂. Herbivores such as cows and sheep will derive this directly from the bacteria in their rumen. Rabbits produce two types of feces - soft and hard - and they eat the soft variety, rich in gut bacteria, as a source of nutrients like vitamin B₁₂. Gorillas are primarily herbivores, but are thought to derive their vitamin B₁₂ from insects, eaten purposefully or inadvertently.

So yes, herbivores derive this particular nutrient from non-plant sources.