Essentially used as horses if you're poorer. Larger than horses and much stronger, a single Onnka can do two or three horses' jobs. Much more common in Occultia as well, since horses were introduced later as Urfens arrived. Horses are used as a status symbol and show of wealth (similar to how rich folk used to have lots of windows) as 1 horse costs 5 times as much as one Onnka and at least twice are many are needed to pull carts.
#TBB
(ref used for horse and rhino anatomy)