PROCEDURE
If possible, have a competent horse handler at the head of the horse, and standing on the same side of the horse as you are.
Standing on the left side of the horse, raise the left front limb forward and cross the limb over the front of the right forelimb and place the hoof on the ground. Time the horse's response. Count the number of seconds it takes for the horse to right itself. Do this several times and calculate the average time.
Now do the same thing standing on the right front side of the horse. Raise the right front fore limb forward and cross it over the front of the left forelimb and place the hoof on the ground.
Walk the horse in a small circle, get them standing square behind and then cross the left hind over the right hind several times. Finally, do the same thing with the right hind over the left hind. If the horse stands crossed for more than a second or two, pull them off balance and note their response.
Count the number of seconds it takes for the horse to right itself. Do this several times and calculate the average time.
TIPS FOR SAFETY AND SUCCESS
This is not an easy skill to master, even for an experienced horseman or experienced vets. It is often difficult to interpret the results of this test because there are many variables that may influence the outcome.
Each horse is an individual and their response to having their limbs crossed may be indicative of their personality rather than a medical condition.
Horses with a nervous disposition often try to normalize their position immediately. More laid-back horses may stand crossed longer. Horses that are excited for any reason try to right themselves more quickly. These differences should be considered when interpreting the results.
I believe that some horses think you want them to stand with crossed limbs, and try to do what you are asking. In other words, we inadvertently teach them to stand with their legs crossed. For these compliant horses, you can pull or push the horse off balance to see how fast they really are able to correct.
Practice this test on your horse when they are normal and healthy to determine their normal response time. This way, you are in a better position to identify an abnormal response.
This test yields more useful results when it is repeatedly performed as an indication of changes or progress.
It helps to have an experienced handler at the head of the horse as you cross the limbs over.
Ideally, you should videotape this test and share it, along with your findings and concerns, with your vet.