I'm sorry to inform you that those cows are going to have a hard time braking on that frictionless surface.
Based on a hike in the Carson National Forest 2 days ago, the only reason a cow is on a frictionless surface is that the cow shat all over it.
Cows can't roll that fast.
Not with that attitude
Spherical cows on the other hand have to move with orbital velocity at least, or they fail to stay in vacuum for long and splash.
It takes a stupid cow, but when they can climb mountains as they do it is not inconcievable that one can roll down.
(I was suprised to see a cow jumping up on a ~3m rock ledge like it was nothing)
However, they can go up stairs, but not down them.
Considering that where I saw it they were doing that unsupervised since at least ~200BC (this being the Illyricum and then Dalmatia), I don't think they have any problems climbing down now.
Cows don't roll - they are frictionless so just glide over the surface smoothly.