When people walk, they usually swing their arms opposite to their legs, so that the right arm goes forward with the left leg, and vice versa. In a four-legged critter that would be considered a trot. If you swing your left arm in unison with your left leg, you would be pacing. However this throws most of us off balance, and results in a zombie shuffle. That is not the case for the quadrupeds. Camelids (camels, dromedaries, and llamas) naturally move in a pace. In horses the ability to pace is inherited, and pacers move faster than trotters. Most pacer can trot but few trotters can pace reliably, so a horse with both gaits will move faster in the pace than the trot. Because the pace is uncomfortable to ride, even more so than the trot, pacers are usually only encouraged in Standard-bred horses used for driving, not riding.
So why do dogs pace?
Never fear, they are not turning into the undead. When puppies pace it probably means very little. They have simply not yet developed the range of movement, or the balance necessary to easily trot or sustain a gallop. They are still trying out different gaits, modes of locomotion. Some puppies never pace, but most do, along with an amble, a waddle, a trot, and various other gaits. They are trying out their legs, and getting used to moving. Rhythm, grace, balance, and endurance are not yet established and like all skill sets require practice.
If your adult dog has recently adopted the pace on the way home from a long walk, you might well worry, but the pace is usually considered a gait that allows an animal to move at speed with less effort, and allows a dog to rest up, without slowing down. Dogs that frequently pace even when not heavily exercised should be observed and evaluated for other indications of pain or discomfort. Conformation flaws can translate into a preference for the pace over the trot. Out of shape animals, overweight dogs and the very young will also adopt the pace.
A sudden change from a trotting dog to a pacer should be mentioned at the next visit to the vet, and the dog should be examined for any spinal or joint abnormalities. But this is usually not an emergency, nor is there generally much to be concerned over; most dogs pace when they get older, or tired, and it is fine.
Some dogs with conformation faults find the pace easier than the trot. These dogs most likely use the pace from puppy-hood, whenever they are tired, and if there are no other indications of a problem, the dog’s camel-locomotion is simply his unique style. Overweight dogs often prefer this gait as well, although there it looks like a waddle no matter which way the legs move.
So next time a dog paces along, don’t worry about it, unless there is another symptom.