Did the primarch ride a horse (before the Emperor found him)

[Trevak Dal]

He's said to have united the tribes of the steppe against Not Rome/China, and that horse (...or implied horse analogues) were life on the steppe, and most primarchs are very big. The Lion and Alpharius and Omegon are the "slightly bigger than a space marine" primarchs, with the rest of them being giants.

 

So...did he ride a horse/horse like critter?

[sarabando]

I would assume so, but once he was a Khan of a few tribes he could probably sit back an guilliman his was to victory.

 

[Dumah]

He doesn't strike me as the type to sit back...

[Marshal Loss]

The Lion rides a horse in Descent of Angels, the "mightiest beast ever bred by the horsemasters of Caliban". Nowhere is the Lion described as being smaller like his brothers (certainly not like Alpharius/Omegon). I think it's fair to assume that the Khan did ride.