While Cushings is more common in horses over 15 yrs of age, it is possible to have pituitary dysfunction in younger horses.
However, the symptoms could also be related to something else. A good exam including lameness and neurological tests would be the first step. And a bit of bloodwork including a resting serum insulin test run on this horse screen for Insulin Resistance and the likelihood of Cushing's. This test is run on a single serum sample run after the horse has been fasted or on nothing but grass hay for 12 hours. If the test is positive for insulin resistance then further testing for Cushing's would be recommended with the symptoms that this horse shows.
Licensed Veterinary Technician