I’d definitely check saddle fit – my mare’s saddle had been fit to her by two different fitters, and objectively passed every test, and yet, she was nasty at the canter, especially if asked to stride out. After she bucked me off, and I broke my knee, I sent her to a pro to stay in work while I was recovering. He wasn’t having issues with her in her dressage saddle, which was made to fit her, but the day he tried the jump saddle, her nasty sister was back.
We finally determined that it was pinching her shoulders when she would stride out, even though it didn’t seem like it would hit there. Sold it, and had one shipped in that fits like the dressage saddle and she’s a different horse.
We missed this issue for a while because she’d also had stifle surgery, and her crankiness showed up on the lunge and under saddle. Her stifles weren’t too reactive to a lameness exam, but when we xrayed, she had OCD lesions. She had surgery, and then the saddle issues cropped up. We kept thinking she was reactive because cantering had been hard for so long because of the stifles. The hard thing for me now is that even though the stifle issues are gone, and her saddle fits like a dream, she’s still reactive in the canter and anticipates that it will hurt.
In short, I let it go on far too long – keep digging on your mare and I bet you will find what it is! Good luck and keep us updated!
He is so much more relaxed and non-reactive. Lesson learned on the Succeed test, next time if I suspect ulcers I’ll just start an Ulcerguard treatment.