Fair criticism, and in regards to minerals especially, I totally failed to mention the need for herbivores to have access to literal rocks and dirt rich in different minerals that aren’t readily available in plant. In captivity, this takes the form of mineral blocks of course.
That’s the answer for cellulose, a tough polymer, but I’d be cautious generalising to iron.
Fair criticism, and in regards to minerals especially, I totally failed to mention the need for herbivores to have access to literal rocks and dirt rich in different minerals that aren’t readily available in plant. In captivity, this takes the form of mineral blocks of course.
Particularly salt, which we usually mix into our food one way or another.