Staright up quackery, there is no real standards for even human chiropractice. There have been no conclusive actual sicientific studies showing it does much of anything on people. The schools are a joke, diploma mills. Get online and look at some studies. Not anecdotal evidence but actual studies.
Anecdotes are the crutch of snake oil salesmen that have no scientific data to back up their claims.
Find a charlatan to dress up and do a dance around your horse while waving feathers and blowing pixie dust in the air. I am sure you can find people that will swear how great it is.
1) My vet is also a chiro and acupuncturist. When I got my mare, her hip was out of place you could clearly see it was uncomfortable her for lope. She was stiff and awkward. If you asked for it undersaddle, you got a bucking fit. A quick adjustment and she was fine. She was also being a total jerk about everything, particularly in touching her withers. Turns out they were completely out of whack and it was fixed last week.
2) I'm not entirely sure what would have happened to me if it weren't for a chiropractor last year. Over the course of a week, I went from having a normal caffeine-deprived-like headache to dry heaving from pain. I had no idea what ungodly force was giving me headaches painful enough to land me in the ER 3 times in a week. The second and third time I wasn't even given morphine, but dilaudid, which is 8x stronger. That was the only thing that allowed me to sleep or eat. When I wasn't in the ER, I was lying in bed in the dark with my head between pillows, trying to sleep because my head was in so much pain. I was given a lumbar puncture and various other treatments for cluster headaches and severe migraines, but the doctors were stumped.
It wasn't until the last ER visit that the nurse suggested a chiro because they had no idea what was wrong. Turns out I twisted a vertebra in my neck from riding. My horse had stopped quickly several times before I was ready and bounced in my saddle hard. It took my chiro 4 seconds of feeling my neck to go, "Were you in a severe car accident?" He cracked my neck and the pain was instantly gone. I stood up like normal and walked out on my own. When I got there, I could barely walk I was in so much pain.
The same thing started to happen this year, but I felt it before it got worse and went and got my neck adjusted again.
In case you couldn't tell, I am a fan of chiropractors.