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.
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown