Horses/17 yr old -change in behavior
I have a 17 yr old paint, we've had for 2 yrs. We got her as a been there done that horse for our then 9 yr old. The first year she was great, a bit of testing but my daughter is pretty horse savy and got her hand over her. She never should sign of kick or buck. She rodeo'd and 4H for a year with her. Then last May she entered a flag team for a local rodeo, she wouldn't come out the gates on time, so we used a lil bump spur on her. That hurried her right up, after about a month of flag team. She was practicing Barrels and Sosa started to buck, eventually throwing her off. Ever since then she bucks often, my daughter has learned the signs and has not been thrown off. Turns her into a spin when she starts bucking. Now just a few weeks ago she started rearing up and then bucking when asked to trot or lope or back up? We have checked her back-made sure the tack was free of stickers or clips, we tried different bits.
I don't know if its just her testing or if maybe she's hurting- will a horse act up in that way if she is hurting ? She seems healthy, she eats well, looks good, no limps or anything.. But maybe arthritis, and Butte would help?
From what you say and the strenuous activities she's been involved in I sort of suspect her back is out, and possibly other things as well. Horses with backs, withers, even hips and shoulders, won't necessarily be lame. You really have to observe how the horse moves, watching how the feet track, over step, etc. It takes a trained eye to do it. But her behavior is definitely indicative of a horse who is uncomfortable. You mention she objects to backing up. That is often a problem with a horse out in the sacral joint. Get an equine chiropractor out and a massage therapist if you can find one. She would probably benefit from acupuncture too. She's gonna have a lot of issues from trying to do what you were asking of her as far as misusing her muscles coupled with being out most likely in multiple areas. This has been building over time and it's gotten bad enough now that she's had it and is displaying the behavior you describe.
So often people mistake a horse's reluctance/slowness/refusal to do something as the horse misbehaving. I haven't seen too many cases where there were no underlying reasons but hundreds where the horse is just so physically messed up that they can't do what they are being asked to do. And the initial indications were ignored or countered, usually with a crop or spur. The rider isn't listening to the horse and after hinting and "talking" the horse gives up and starts "yelling" ie misbehaving severely.
Let me warn you in advance that this problem didn't happen over night and won't be fixed with 1 or 2 visits from the chiropractor and anyone else you can find. The massage therapist can straighten out the muscular problems which will help the chiropractic adjustments go easier aned hold longer. Same with acupuncture work. The therapies are complementary.
Best of luck with her and don't give up. She sounds like a nice mare who, yes, is getting up in years and may well have some arthritic issues as well but that's not all you are dealing with now. And stuffing the horse full of bute isn't the answer,it isn't even all that effective at masking the discomfort. Plus being really hard on the stomach. Addressed correctly this can be resolved and the horse able to perform well for a long time.