Forced March on a Mount. So how does Forced March work on Horseback?

Does the horse suffer exhaustion? Does the rider? 

Assuming It's only the horse, then parties will always travel extra hours until the horses get exhausted... no penalty to them.

One more question: If the party fears no danger, in a relatively safe area, is there any penalty to going at a fast pace? In many cases, Perception is not necessary... Is perception the only penalty to perception?