My percheron was a roarer. He had surgery done to sever one vocal cord. I believe this was his left one. They had to do a tracheotomy and he has a large lump of scar tissue in his throat because of it. It is about a foot down from his throatlatch.
The surgery for roaring worked, but they caused him to have a cleft palate. I had to have him scoped because he kept leaking green slime from his right nostril. The hook blade that they used for some reason sliced his soft palate and caused a man made cleft.
I think this is an extreme complication though. I have read that most times the surgery is very successful.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.