I don't know if they did the specific things you mentioned, Walknthewalk. I just trusted them to know what to do for anything horse related. They specialize in only equines.
Sometimes even the best vets in the field can mis-diagnose or not run tests for something weird.
I love love love my equine vet, who also happens to be a leg specialist. Everyone in this entire area (from poor retired folks like me to the owners of expensive show horses to his peers) recognize he is tops in his field and how privileged we were the day he moved into our county
My foundered horse ended up with torn ligaments and sesamoiditis in both front legs because the expensive and well-schooled rehab farrier cut his heels too low in one strike. My Walk-on-water vet took X-rays and ultrasounds to prove all that.
The torn ligaments happened in July, 2012. By December, 2012 my vet said my horse's legs had completely healed, he was not in pain but he healed crooked and would never walk without a limp again. You can imagine the tears I shed over that one
There were no X-rays or ultrasounds this time, the diagnosis was purely visual and included watching the horse walk.
I sent pics of the legs and hooves to someone on this forum who quickly e-mailed back, stating my horse's legs were NOT crooked, he had healed properly on both sides. I was told what I needed to do with the hooves in-between Trimmer visits, which are at 4-week intervals.
My horse was just trimmed on 02-15-13, this video was taken 02-16-13. He is a Tennessee Walker, therefore gaited. He was foundered 8-9 degrees on the LF and 5 degrees on the RF.
Thanks to the help I received from someone on this forum, this horse has gone from me thinking I may have to put him down to now being very very close to being ridable. MEANING, he did NOT heal one leg shorter than the other as the best vet in the area said he would.
It was all in his heels and thanks to me being instructed, from afar, on what to do with his hooves until the Trimmers came again, he is more sound than anybody would have ever imagined.
The proof is in this video
He still needs a chiro for some adjusting on his fractured sacrum (another story:( but she's still on pregnancy leave. He is licking/chewing because he's asking permission from the strong Alpha horse to go ahead of him into the main pasture who is also my 25 yo TWH with EMS:) I burned up your reading time with this to say, don't take the specialists words.
If you have the option, get another vet, from another facility, and ask for blood draws to check for any sort of metabolic issues, EPSM, and any other off-the-wall disease that might cause this horse to not want to hold his weight.
Another thought is hind gut ulcers. I know he was scoped but that was for gastric stomach ulcers. Find out if they also checked him for hind gut ulcers.
Unless he's colicked on you, I sort of doubt he has hind gut ulcers but each horse reacts different to things.
I doubt that needing chiropractic help would be a cause of constantly losing weight but it is possible. It certainly wouldn't hurt to have a chiro look at him because the stress of pain anywhere in the body is capable of producing strange side effects
And, as Spotted commented, it could be something as simple as not getting enough hay - wouldn't that be a terrific and simple fix
Most horses need 1.5% - 2% of their desired body weight. I feed my hard keeper, with EMS, a lot more than that when he comes in at night. He comes in around 6:30 PM durig the winter and gets a mixed grass hay, so I load him up. He always has some hay when I get to the barn at 7:00 AM. I also feed him soaked timothy pellets this time of year since, even on 22 acres, pasture quality isn't that great.