Would my horse always tell me if her tack doesn’t fit correctly?

[sbloom]

There is a school of thought that bucking is from nerves firing incorrectly, nerve pain, and that can happen from compensatory movement from pain elsewhere. An un-muscled shoulder (eg spine of the scapula visible, rather than a rounded smooth shoulder) makes it more likely that nerves are being compressed between the shoulders, spine and ribcage. Again, just one of the current best theories.