I would use a welded wire mesh instead. Like you said, conduit pipe bends really easily. I wouldn't really trust anything not meant for horses. A horse could roll or aim a kick at another horse and get a hoof stuck as the bars bend. I have heard of horses getting hooves stuck in between bars even made for horses, and wouldn't want to risk it with some possibly "dangerous" bars.
I would recommend using welded grill wall or live stock panels.