Simply put, bed bugs consume blood. While they don't care whether it's human or animal, they prefer human.
Transcript of What Bed Bugs Eat
A bed bug doesn't care whether its human or animal. They do prefer human however because we don't have as much hair, it's easier for them to get to our skin and penetrate to the blood supply. If there is no humans available they have been known to feed on animals such as rats, cats and dogs.