Honestly, I'm a 34 DD, and sometimes I just suck it up and wear two sports bras. However, I just tried a playtex 18 hour with no underwire, and so far so good for riding. It just gives you that 70's torpedo boob look, but who cares at the barn??
"My treasures do not clink together or glitter; They gleam in the sun and neigh in the night."