I, too had a problem with thumps early in my horse's career. Dr. Sue Beal
recommended doubling the dose of electrolytes and switching to a good free
choice loose salt and separate loose mineral. I now use Redmond salt and
Rushcreek 1:1 mineral available from ABC's. No more thumps. (knock on wood)
That was 2 years ago. Good luck.
Sallie and Matty
www.cisnet.com/Mateef