Yes, by taking out "as" you're constructing a totally different sentence. "As," used here, means "for example." So "graze: feed as in a pasture or meadow" means "graze: feed, for example, in a pasture or meadow." By taking out "as," you will change the sentence to mean: "Feed (ONLY) in a pasture or meadow," restricting the place of grazing to pastures or meadows only, rather than using pastures or meadows as examples.