Chapter 121Walking Horses
The Tennessee Walking Horse, commonly called the Walking Horse, is a light horse breed developed in middle Tennessee for use on southern plantations during the eighteenth century. The average Walking Horse is 15 to 16 hands tall and weighs 500 to 600 kg. The Tennessee Walking Horse is a composite breed, created by crossbreeding Canadian and Narragansett Pacers and Morgan, Standardbred, and Thoroughbred horses. The Tennessee Walking Horse Breeders’ and Exhibitors’ Association was formed in 1935. Because of the versatility of the Walking Horse, along with a characteristic racking gait within the breed, a second breed association was recognized in 1971, the Racking Horse Breeders’ Association. Members of this group of horses are commonly referred to as Racking Horses.
A Walking Horse performs three gaits: the flat-foot walk, running walk, and canter. Both walks are four-beat gaits, with one foot up and three feet in various phases of striking the ground. The footfall sequence is left hind, left front, right hind, and right front. High-stepping forelimbs with an extended reach characterize the flat-foot walk. The hind foot overreaches the imprint of the front foot by 15 to 55 cm in a straight, smooth, gliding motion. This overstride is unique to the breed and is referred to as the big lick. The horse’s head and neck nod, and the ears flick forward and backward in rhythmical fashion with the rise and fall of the front feet. The appearance is that of pulling with the forelimbs and driving or pushing with the hindlimbs. The speed of the flat-foot walk is from 4 to 8 miles per hour (6.4 to 12.8 km per hour). At the running walk, the gait is basically the same but faster (10 to 20 mph [16 to 32 km/h]). The canter is a three-beat gait, with a left or right lead. In the canter the horse lifts the forehand, giving an easy rise and fall, in a rolling motion. The gait is referred to commonly as the rocking-chair canter because of the high, rolling movement of the horse’s body.
The Racking Horse gait is a bilateral four-beat gait, with one foot striking the ground with the other three limbs in various phases of elevation. The gait often is referred to as the single-foot gait. When shown, a Racking Horse performs the show walk, slow rack, and fast rack. The show walk is a smooth, collected, slow and easy four-beat gait. At the slow rack the horse’s head is held with the neck arched and ears erect. The fast rack is similar in form to the slow rack, but the horse displays speed and leg action. The natural head nod must not be exaggerated at the slow or fast rack.
In both breeds the collected gaits of a show horse (a gaited horse in performance shoes and tack) shift the center of gravity caudally, compared with most other light breeds, with increased loads on the hindlimbs resulting in a high incidence of hindlimb lameness.
Both breeds are used for show, trail, and pleasure riding. Horses are shown at halter, in harness, and under tack, with English or Western saddles. Horses that are shown wear a light shoe similar to a standard keg shoe, a plantation shoe, or a performance shoe, depending on the class. The plantation shoe cannot exceed 3.8 cm in width and 1.3 cm in thickness, and the heel calk cannot exceed 2.5 cm in height. The performance shoe, or stack, is a shoeing technique used to accentuate the show horse gaits. The shoe is constructed of several layers of flat or wedge pads, stacked one on top of another, placed between a nail pad at the solar margin and a metal shoe on the contact surface. Pads are made of leather, plastic, or hard rubber. The amount of height or extension the shoe provides must not exceed 50% of the natural hoof wall length, measured from the coronary band to the tip of the toe. Pleasure horses are commonly flat shod.
Although the highest population of Walking and Racking Horses is presently in the southeast United States, they are becoming more popular across North America, especially for trail and pleasure riding, because of the physical endurance and gentle disposition of the breeds. The show season generally is considered to be year-round, picking up in the spring and peaking in the fall with the national championships. The Tennessee Walking Horse National Celebration is held in Shelbyville, Tennessee, each year and is an 11-day event ending with the crowning of the national champions on the Saturday before Labor Day. The Racking Horse Celebration is held each year in Decatur, Alabama, during the last 2 weeks in September.
Lameness evaluation of a gaited horse is best performed with the horse under complete tack with a rider. It is impossible to duplicate the head set, balance, and shifting of the horse’s center of gravity caudally without a rider. The horses generally exercise in a large, oval arena, and to perform a good evaluation, one needs to provide a place where the horse has room to work in all gaits. The ground surface in this area should be firm. A veterinarian’s impression when evaluating a show horse for the first time will be that the horse’s problem must be in the forelimb and more specifically the foot. In light of the negative publicity the stacked shoe receives, focusing one’s attention on this area is easy. Even as the horse is walked at halter, this impression may not change, because of the awkward nature of the horse handling the bulky shoe. In our experience, few problems are associated directly with the shoe, except hoof wall avulsions, when the shoe is accidentally pulled off in the show ring. Measures to control bleeding must be taken immediately, followed by good wound care. Hoof wall composites then can be used to restore hoof wall function. If an elevated shoe is removed completely and suddenly from an immature, developing horse early in training, removal causes a dynamic mechanical flexural deformity. The horse knuckles over at the fetlock joint because of the pain associated with pulling of the deep and superficial digital flexor tendons.
Unfamiliarity with the standard gaits of Walking and Racking Horses, especially when shod with a stacked shoe, may result in confusion with ataxia, particularly at faster speeds. However, anecdotally, our impression is that a high incidence of cervical vertebral malformation does indeed occur in Tennessee Walking Horses, so this should be kept in mind.
Tennessee Walking Horses are stoic and seem to have a high pain tolerance. Problems encountered in flat-shod Walkers or Rackers mirror the lameness problems seen in other light breeds; therefore the following discussion focuses on show horses in stacked shoes. The hoof tester evaluation is of limited value on the front feet of performance-shod horses. Careful palpation and manipulation of the limbs are performed routinely. Careful evaluation of the foot and shoe should not be overlooked. Use of pressure-shoeing techniques by unscrupulous owners and trainers causes soreness and increases the big lick, conditions that occasionally arise in a performance-shod horse and should not be overlooked. The technique is performed by overtrimming the hoof wall and thus increasing sole pressure. A carefully placed nail in the nail pad encroaching on the sole or the sensitive laminae may be noted. A foreign object, such as a stone inserted between the pad and the sole, inflicts discomfort. Assessment of digital pulse amplitudes, tapping on the hoof wall with hoof testers or a shoeing hammer, and response to nerve blocks may determine the problem.
Problems seen in the forelimbs commonly are associated with imbalances in the shoeing, leading to an uneven height of the forelimb carriage. To evaluate the forelimb carriage, the observer should draw an imaginary line at the chest level, watching the carpal action to determine which leg is carried lower to the imaginary line as the limb advances, indicating the problem limb. When this problem is detected, careful evaluation of the shoeing technique and comparison between limbs are indicated. Correction of foot imbalance may resolve the problem. Osteoarthritis of the distal interphalangeal joint (low ringbone) frequently is seen in older horses but is not always correlated with lameness. Proximal suspensory desmitis usually is caused by slipping while shod with an elevated shoe and may be associated with localized pain on palpation. Bicipital bursitis is seen occasionally. The horse may have asymmetry in shoulder motion and pain on palpation of the area, especially when the limb is raised. Abduction or adduction of the shoulder is performed. As in most breeds, sole abscesses are common in flat- or performance-shod horses, as is laminitis.
The highest percentage of lameness seen in our practice with Walking and Racking Horses is associated with the hindlimbs, because of loading of the hindlimbs during exercise. As each hindlimb strikes the ground and the horse’s weight is carried through the stride, a rotational, twisting motion also is seen throughout the entire limb before the leg is advanced. This is especially noticeable in the Walking Horse at the faster gaits. The shifting weight and the twisting motion increase stress on the joints and surrounding support structures. Osteoarthritis of the distal hock joints and stifle is common. A positive response to the Churchill test is helpful in isolating pain to the distal hock joints. Careful palpation of the medial patellar ligament is particularly important in this type of sports horse, because at one time almost all of the show horses were subjected to medial patellar desmotomy with hopes of improving the overreaching stride of the rear legs. Although the medial patellar desmotomy site only occasionally is found to be the origin of the lameness in these horses, the possibility should not be overlooked. The practice is not as common today as in the past; however, many trainers from the old school feel that having the desmotomy performed is important. Upper- and lower-limb flexion tests are performed. Local analgesia is used to define the source of pain. Trochanteric bursitis occurs in Walking and Racking Horses and is related to the rotational, twisting motion of the hindlimbs. The horse has pain on deep palpation over the greater trochanter of the femur, during upper limb flexion tests, and when the hip is stretched forward or backward, abducted or adducted, and rotated.
Other conditions are encountered in these horses. Some have muscular weakness in the hindlimbs, especially young unconditioned horses. When weakness is combined with straight hindlimbs, instability of the patella is common. Chronic hip and stifle soreness caused by a trailer on the outside of the shoe may be an underlying cause of lameness. Osteochondrosis occurs in the forelimbs and hindlimbs. We see a substantial number of horses that are thought to be lame but have equine protozoal myelitis.