Run would work, as would Endurance. Should we give it some sort of ability to increase its ability to move through heavy foliage? Something like:
Forest Movement (Ex): An okapi's skill at moving through heavy foliage is such that it suffers no movement penalties from light undergrowth and treats heavy undergrowth as light undergrowth. An okapi is still affected by magically enhanced plants that slow movement, such as an entangle spell.