A bulo is a big, dumb animal that is constantly moving. While it is trainable, calling a bulo trained is like saying you taught a fish to swim--the animal simply walks forward, no matter what is in front of them, veering only when a tall object jutting out it can't climb is in front of it.
The mating of buloes only occurs when a male and female come in direct paths. Originally the bulo population in the Avantsphere was scarce, due to easy predation and the came close to non-existent due to sprawl, but after the Peace Wind some upstart individuals saw the doddering dolt's worth and began breeding them like mad. Now they've grown only more docile under human care for use in labor.
The can pull eight times their own weight without losing pace at their slow plodding speed. This means they find great use in the shipping services for brigands big enough to defend them. Buloes are not ideal for transport, however, as no matter what the rider may do a bulo's speed will never change.
In the distance if you ever see a swarm of corvi and dingle dogs making a ruckus, it may well be because a bulo slowly trotted itself straight off a cliff.