If your vet didn't give shots for any reason you'd better be running tests to get to the root of the problem.

Trainers always think horses are lazy...just like their owners j/k

If you think their is a real problem you'd better find out before pushing your horse in training sessions ruins her physically/mentally.

Get the test done first huntseat is right my friend lost her horse because the trainer told her to push him more.  The horse turn out to have e.p.m  the horse was to weak for the treatment to work 

Have a selenium test done on the horse. My horse would not move forward for several months and I found out he was tying up from lack of selenium.

It's a relatively inexpensive blood test, compared to testing for EPM which has similar hind-end symptoms.

Blood test for iron - but it's EXTREMELY rare for a horse to have that kind of problem unless they are a bleeder (race horses primarily).