If you do bathe your horse I can guarantee that it will roll and roll the moment you let it loose.
Haha that's pretty much the rule kinda like how the white/gray ones tend to get the muddiest.
But seeing as how it is very very muddy out here now I would probably wait to bathe until it dried up a bit. I don't know where in MN you are located but I am in the far east twin cities metro and our pasture is basically a lake right now. You can see where my girl's blanket is as everywhere the blanket isn't is the wonderful color of mud.