My horse had some chiropractic work done when she was having problems with her canter transitions, turns out her lumber wasn't able to move laterally very well, which my vet never even thought of. Now she's amazing! Just find the right chiropractor!
Chiropractors have done wonders for my horse, but I definitely would have a separate vet and chiropractor.
I've had good experience with them ! Our horse hated to canter and he's like a new horse!
I have a separate vet and chiropractor. My OTTB get done once a month and is fine. I only used a vet chiropractor once and wasn't very happy. My horse just got sore within a few days, it didn't make anything better.
I agree with samantha in terms of finding an specialist. With someone who knows exactly what they're doing horse chiropractors can work miracles for horses.
Chiropractors are great. however, most vets who do chiro work aren't that great. I would suggest finding a vet who specializes in chiro and had actually gone through extensive training.