@DragonRider45 Well, it's convenient that they died centuries ago then, isn't it?
The creature used to be called simply "mare" or "mære" (and it's the origin of the word "nightmare"), but with time they have been imagined as riding horses or being horses themselves because of the homophony. Particularly in the Henry Fuseli painting that Okayado himself parodies at page 5.
@zectians yeah if you could get a hold of the centaur milk then it may be possible to clone them and maybe create a new species on earth. Blood would probably be easier to use for cloning purposes though, but then again I am not sure one way or another. There should be enough DNA within a glass of milk for cloning purposes if it is properly used before it goes bad, but even then it may be possible to retrieve enough DNA hopefully should that situation occur.