Quite often, the diagnostic tools and techniques at the disposal of your mobile veterinary service are all that are needed to solve the mystery. Some horse owners have been through this routine a time or two: Your vet will ask to see your horse move on a straight line and on a circle, then on a hard surface and a soft one. He or she will ask when you’re most likely to notice the gait abnormality: At a trot or at a canter? At the beginning of a workout or at the end? Can you think of any incident that might have caused an injury such as a particularly hard gallop or getting a hoof caught in the fence?

The veterinarian might begin by palpating the leg, gently squeezing the tendons and ligaments or probing the texture of a knee or ankle with his or her fingers, looking for subtle signs of inflammation, and/or he or she might use hoof testers to put pressure on the sole of Boomer’s foot, looking for a sensitive spot. He or she might employ flexion tests, where the horse’s leg is held in a position of maximum joint flexion for a minute or two, then he’s asked to trot out briskly, a technique that can highlight some types of lameness.

If these methods don’t reveal the source of the complaint, most veterinarians will suggest they “block” the leg with injections of a local anesthetic, starting down at the ground and gradually working up the limb. After each injection, the horse is walked and trotted until the anesthetic has numbed the nerves in the problem area and the horse moves soundly. Very often, this time-honored technique helps zero in on the location of a lameness, but it won’t tell you exactly what’s going on in there. For that, your veterinarian might have to get high-tech help.