We don't domesticate rhinos, but their body type, like the oxen, is built for great weight. Rhinos have comparatively thick leg bones, stout and low to the ground. Burden beasts bend more at the joints than horses and deer - bent structures diffuse weight better (this is why our femurs bow in to the knee instead of going down straight). The back of the skull is flat and the spines of the vertibrae extended for powerful neck muscles. That head is heavy!