i have a 4 year old paint gelding, hes about 16.2hh and really sweet. hes not fully broke, but hes a nice ride. but i noticed he bobs side to side and the faster he goes in a walk the worse it gets. but when hes trotting it stops and he holds it high. i got him this past may and hes never bobed then, it started when we got my 3 year old Paint, h edose it in the saddle and on the ground, when hes hyper and wanting to go back to the pasture and the other 2 hroses he has more of a bob.
what could cause it?