When I arrived at my client's barn I noticed my 4 legged client looked quite different than the last time I saw her about 20 months ago. Where she used to be convex on all saddle bearing surfaces, she was now concave. My updated tracing showed a different horse than I had seen or than the saddle seller ever saw. The story was that this mare had lost about 300 lbs and was now back to working 3rd level dressage. The cause of the weigh loss was never clearly diagnosed and there had been 2 barn changes in the meantime. I was called because the chiropractor thought there may have been something going on with her saddle.
To the layman's eye the saddle looked good from the front and back. The trainer didn't have any problem with it. What had never been noticed was that this saddle was now pivoting in the center, under the rider's seat, and hanging there on there horse's spine. My exam before I placed the saddle on this poor horse's back yielded drastic pain reaction to pressure on both sides from the end of the withers through to about the sacrum. Neither the owner or the professional trainer were aware of any problem.
My Point in relaying this story is that a saddle should never even be placed on a horse's back if a horse has gone through body changes if the saddle fit has not been evaluated by a professional saddle fitter. To the eye, this saddle looked acceptable by what most people would judge. That this horse is working 3rd level dressage, lifting her back and incurring pain each time, is certainly what no owner, including her owner, would ever want if they understood what they had been asking.
If you are aware that your horse has changed weight, either up or down, be sure to have a saddle fitter take a look before you put that saddle on again. Even if it looks good, a saddle fitter knows aspects of fit that trainers and riders are not aware of. It can save your horse unnecessary pain and can save you future vet calls.