Lameness in Draft Horses

Chapter 125Lameness in Draft Horses



Dallas O. Goble


The draft horse today enjoys a position in the world far different from when it was considered primarily a work animal. Draft horses supplied power for farming, transportation of commodities, lumbering, road building, and all such tasks until the 1930s, when the gasoline engine essentially replaced the horse. Isolated areas still continued to use the draft horse for farming and some lumbering activities until the early 1940s. After this period, draft horses were used primarily for specialty areas such as movie production, theme parks, parades, and frontier celebrations. But in some communities, religion and family tradition mandated the continual use of draft horses as a power source for farming. During the 1950s and 1960s, draft horses decreased in numbers in the United States, and subsequently the genetic pool was decreased. Draft horses started gaining popularity in the late 1970s and early 1980s and have once again become a popular member of the horse industry.


Draft horses today are different from those of the early 1900s. They perform different functions and are owned for a different purpose. Owning a draft horse is far more likely to be simply a hobby than an economic part of the family income. Many horses are used strictly for show purposes in classes such as halter, fine harness, and equitation, or for parades and advertising. Draft horses are used for trail riding, pleasure riding, fox hunting (often crossbred with Thoroughbreds), and other pleasure uses. In some mountain areas where selective lumbering of individual trees is undertaken, draft horses are still used today. With a resurgence of interest in mules, draft horse mares often are used in the breeding programs. Draft horses frequently are crossed with Thoroughbreds to change the genetic pool for the breeding of large hunter, jumper, and Three Day Event horses. Pulling contests are popular in certain areas and represent an additional use of the modern-day draft horse.



Modern-Day Draft Horses


The most important physical change of the modern-day draft horse is its size. In many modern breeding operations, size is the main criterion used for selection. When draft horses were used predominantly as working horses, the average weight was 680 to 775 kg (1500 to 1700 lb) and the average height was 1.6 to 1.7 m (15.5 to 17 hands). This size was optimal for the multipurpose activities these horses performed on most farms and ranches. They pulled the plow, mowed and racked hay, helped round up cattle, and often took the family to church on Sunday. Draft horses today are more frequently in the range of 820 to 1000 kg (1800 to 2200 lb) and measure 1.8 to 2 m (17.5 to 19.5 hands) in height. As a result of selection based on size as the dominant characteristic, conformation and quality have suffered in some respects. Distribution of lameness also has changed. Foot size and quality have not increased proportionately with body size and weight. Osteoarthritis (OA) is common in draft horses and likely is related to body size rather than the use of the horse. Hybrid vigor, once thought to be advantageous, has decreased by using the practice of line breeding for selected traits. The large size of a draft horse sometimes misleads one to think the horse can withstand greater stress and disease than can light horses, but I have not found this to be true. Draft horses may not recover as well as light horses with the same injury or disease. Because draft horses have a tendency to be stoic, recognizing a severe problem early in the disease process may be difficult. This tendency may cause a costly delay in diagnosis and management. The physical size of draft horses today has hindered veterinary care and treatment. Veterinarians tend to be unsure of drug dosage and appropriate treatment schedules because of the large body size. Many hobby horse owners do not have facilities adequate to handle a 1000-kg horse and may not be knowledgeable in draft horse care. Draft horses are not always well trained or easy to handle, and owners are sometimes unable to lend assistance when needed. These facts have curtailed the interest of many practicing veterinarians who have difficulty rationalizing being stepped on by a 1000-kg draft horse as fun. In addition, finding high-quality foot care for a draft horse is sometimes difficult, because most farriers are experienced with light horses. Farriers feel similar to veterinarians: “Why hold up a 1000-kg horse twice as long as needed to hold up a 500-kg horse?” In addition, farriers who shoe draft horses have to stock nails, shoes, and bar stock often on special order or low-volume items, a fact that dramatically increases overhead expenses. Thankfully, some veterinarians and farriers are willing to treat and specialize in draft horse care.


The following discussion related to draft horse lameness reflects my personal clinical experiences and not necessarily what may be in the equine literature. Lameness distribution may vary from my observations depending on the use, location, individual draft breed studied, or other factors associated with different populations of horses.



Lameness Examination


Diagnosis and management of lameness in a draft horse may seem more intimidating simply because of the large size of the horse and the infrequency with which requests are made for examination compared with light horses. In reality, draft horses experience the same problems as do light horses, although the distribution is different, and the principles of diagnosis and management are the same. The lameness examination is the same as in light horses, and any deficiency of hands-on experience can be overcome by a systematic and thorough examination. Palpation of peripheral nerves (palmar and plantar digital nerves, in particular) can be difficult because of thick skin and hair, and veterinarians are sometimes reluctant to attempt perineural or intraarticular blocks. The anatomy is the same, but the ability to palpate the nerves is diminished by these factors and also by subcutaneous thickening that some draft horses develop in the lower part of the limb.


Draft horse lameness diagnosis and management lagged behind those of light horses for many years. First, as long as the horse could still accomplish farm work, less concern was shown for a horse that limped slightly. Possibly the person behind the plow or cultivator also limped and accepted it as part of doing the job. Second, economic considerations were a major factor in the farming operation. This does not reflect necessarily a lack of care, but it was simply an accepted part of working in that day and time. But today, draft horses are afforded the same concerns and care given to the light horse, and only modification of most treatment protocols needs to be made.


Detailed description of the lameness examination can be found in earlier chapters. Special attention should be paid to several critical points, however. Draft horses are more stoic than light horses, and as a result lameness may be advanced when first recognized. For example, draft horses with OA of the proximal interphalangeal (PIP) or distal interphalangeal (DIP) joints may have severe radiological changes, but the owner may report that the horse only recently showed signs of lameness. Granted, many owners are inexperienced, but even the experienced owner may not recognize a problem until it is well advanced. This can be explained partially by the fact that a draft horse often is used at a gait (walk) that makes lameness less obvious, and the horse frequently is hitched with one to seven additional horses, and an individual horse’s problems are less discernible in a group.


When possible, observing the horse at a walk and trot on soft and hard surfaces is useful. Hoof tester examination, in my experience, is less reliable in draft horses than in light horses. Small hoof testers are of questionable value. Even with long-handled hoof testers, it is difficult to apply enough pressure to produce a positive response. Foot lameness should be suspected if a horse shows grade 1 of 5 lameness on soft footing but grade 3 of 5 lameness on a hard surface. The examination always should include backing the horse at least two or three times and observing the horse at the walk and trot in a circle and in tight turns. Sometimes conditions such as shivers, stringhalt, or intermittent upward fixation of the patella are seen only during these maneuvers.


Lower limb flexion tests are less rewarding in draft horses than in light horses. It is difficult to apply sufficient pressure during the flexion test to accentuate pain in this region. A draft horse may be less willing to trot after a flexion test, making it difficult to determine a true positive response. Most light horses will trot after flexion, even when the reaction is highly positive, but a draft horse will not trot off as readily without strong urging. In addition, draft horses often are not accustomed to being trotted in hand routinely. Hindlimb upper limb flexion tests in a draft horse are a more reliable indicator of hindlimb lameness than in a light horse.


I prefer to perform diagnostic analgesia with the horse in a standing position, rather than having an assistant elevate the limb. This is especially true when attempting palmar digital nerve blocks or palmar nerve blocks at the base of the PSBs. Palpating anatomical landmarks in this area when a draft horse is bearing weight is easier than when the limb is elevated. To maintain the limb in an elevated position or to restrain the limb in this position can be difficult. Adequate restraint usually can be achieved by the application of a nose twitch.



Ten Most Common Lameness Problems


Over several years I evaluated 745 draft horses admitted with a chief complaint of lameness. The following list shows the top 10 lameness conditions that I observed in order of decreasing frequency (33 horses had other problems):


































 1. Foot lameness (abscess, hoof cracks, laminitis, and sidebone) 260
 2. Tarsal lameness (osteoarthritis, bog spavin, and osteochondrosis) 207
 3. Splints 84
 4. Tendonitis and suspensory desmitis 45
 5. Osteoarthritis of the distal interphalangeal or proximal interphalangeal joints 44
 6. Fetlock lameness (sesamoiditis, osteoarthritis, and osteochondrosis) 23
 7. Thoroughpin 18
 8. Carpal lameness (traumatic or infectious carpitis) 13
 9. Stifle lameness (traumatic, upper fixation of the patella; osteochondrosis) 10
10. Myopathy 8


Lameness Common to the Forelimb and Hindlimb



Foot


The foot is the most common source of pain causing lameness in draft horses. A thorough and complete examination of the foot is paramount to diagnosis and management of lameness. Hoof quality and conformation have suffered in modern-day breeding selection, and as a result we tend to have large horses that are supported on feet that lack hoof size and quality. I suggest that breeders of draft horses give strong consideration to hoof conformation when making critical selections for breeding programs.



Subsolar Abscess


The most common cause of foot lameness in a draft horse is a subsolar abscess, a problem most frequently encountered in a forelimb. The high incidence of subsolar abscess formation in draft horses can be related to several factors. First, obtaining consistent farrier care may be difficult in many locations, and foot care may be neglected. Second, draft horses often have poor hoof quality and easily develop hoof cracks or severely chipped and broken hoof walls. Clydesdales have particularly poor hoof quality. Many draft horses have dropped soles, predisposing them to bruising and subsolar abscess formation.


A pair of large, good-quality hoof testers provides the simplest method of determining the location of the abscess. Tapping the hoof wall or sole with a hammer (or the hoof testers) can help locate the abscessed area. In horses that recently have been shod or reset, each nail should be examined. An abscess associated with a nail usually develops 5 to 11 days after shoeing. Hoof cracks causing instability of the hoof capsule can cause lameness even though the area of abscessation may have resolved. If a foreign body is lodged in the hoof (nail, glass, or other penetrating object), a fistulogram (contrast radiograph) should be performed. A subsolar abscess can become a life-threatening problem if osteitis of the distal phalanx develops or penetration of the DIP joint, deep digital flexor tendon (DDFT), or navicular bursa occurs. Proper diagnosis is mandatory; otherwise, the long-term prognosis becomes worse.


Once the abscess is located, the sole should be pared with caution, especially if the horse has a dropped sole or has a concomitant full-thickness hoof wall crack. Overzealous sole paring may result in extensive mechanical damage to laminae and loss of hoof wall strength. Adequate drainage is paramount, but removing a large amount of sole is not necessary, even when substantial undermining has occurred. In draft horses, it is important to err toward a conservative approach, at least initially. Thorough flushing of the foot with povidone-iodine or chlorhexidine diacetate solution should be done at least once a day for 3 days or until the drainage has stopped. The foot can be soaked in a saturated solution of magnesium sulfate for 3 to 5 days to reduce inflammation and to aid in drainage. Finding a soak boot large enough for draft horse feet at a reasonable cost is difficult, and I have found an easy solution by using a 1 m length of truck tire inner tubing. The tubing is slipped half its length over the foot, and then up the leg, with the remaining half doubled back up the leg and secured in place by a wrap of choice (Figure 125-1). The tube then can be filled with the soak solution. Draft horses with an uncomplicated subsolar abscess do not need to be treated with systemic antibiotics. However, if cellulitis of the coronary band and pastern region is present, the administration of antibiotics is indicated. Trimethoprim-sulfadiazine (15 mg/kg orally [PO] bid) or ceftiofur sodium (1 mg/kg intravenously [IV] bid or intramuscularly [IM]) is my usual choice. Judicious use of nonsteroidal antiinflammatory drugs (NSAIDs) is indicated, but these drugs should not be used for extended periods of time or at levels that may mask a more serious problem. Phenylbutazone, 4 g PO or 2 g IV, on the first day is sufficient. Thereafter, 3 g and then 1 g are given orally on the second and third days, respectively. A tetanus booster should be administered if the horse’s vaccination status is not current or is unknown.


image

Fig. 125-1 Draft horse with rubber inner tube in place and used as a soak boot for a foot abscess.


If the horse’s condition is not improved in 3 days, the horse should be reexamined. Radiography and positive contrast fistulography should be performed. A fistulogram is performed using contrast material administered through a Foley catheter. The foot should be held off the ground when contrast medium is infused and should be held up for 2 minutes thereafter. The foot is then placed in a weight-bearing position, and radiographs are obtained immediately. During weight bearing, a fistulous tract often is closed by soft tissue compression. If deeper structures are involved (DIP joint, DDFT, distal phalanx, or navicular bursa), an extensive treatment program is initiated, including bacterial cultures, surgical drainage or curettage, lavage of the affected area, and the administration of broad-spectrum intravenous antibiotics. The initial antibiotic treatment usually includes 20,000 IU of potassium penicillin per kilogram four times a day and 6.6 mg of gentamicin per kilogram once a day. Bacterial culture and susceptibility testing results may require changing the antibiotic regimen.



Hoof Wall Cracks


Forelimb hoof wall cracks were found in 67% of the 260 draft horses examined for lameness of the foot, although not all were the primary cause of the horse’s current problem. Full-thickness hoof wall cracks need to be stabilized when they cause lameness. The crack should be cleaned carefully and curetted, and normal hoof wall should be present on each side of the defect. The technique of dovetailing may provide additional support if hoof repair material is used. Dovetailing is accomplished most easily using a 1-cm (image-inch) round burr on an electric drill and undermining the hoof wall at about a 45-degree angle, leaving a shelf of hoof wall down to the white line on each side of the defect for the full length of the crack. This provides additional surface area for a stronger repair and reduces the likelihood that the repair material will come out. Care must be exercised to avoid damage to the sensitive laminae or to create bleeding during this procedure because these may predispose to abscess formation beneath the repair material. If the horse is initially unshod, a shoe with clips may be sufficient to provide support and to immobilize the defect. Radiator hose clamps and 1-cm long, No. 8 metal screws can be used to stabilize the crack. Because infection is often a problem, the radiator clamp method can be used initially, when filling the defect with repair material is contraindicated. Antibiotic-impregnated repair material has been used, but my success with this material in draft horses has been limited, and my preferred method is a shoe and the radiator clamp and screw combination. It is important to have at least two screws through each piece of clamp and on each side of the defect to add stability. The top clamp should be placed at the proximal limit of the crack. I generally space the clamps 1.9 cm (image inch) apart, and the number of clamps needed depends on the length, depth, and amount of instability in the crack and on the size of radiator clamp used. The clamps are removed as the defect grows and are replaced if broken. The clamps must be tightened carefully, because lameness from laminar pain will be worse if the clamps are too tight. This problem is corrected by adjusting the clamp with a screwdriver.



Laminitis


Laminitis in draft horses is a serious lameness condition, and prognosis for complete resolution often is guarded to unfavorable. Regardless of the cause (e.g., grain overload, colitis, metritis, retained placenta, toxemia), once the pathophysiological process of laminitis is in motion, the end results are similar. The solution to the primary cause often is solved more easily than the secondary problem of laminitis. This is especially true in mares with retained placenta, in which the retained placenta and metritis are solved easily, but secondary complications may be devastating. Many of these mares develop severe laminitis with distal displacement (sinking) of the distal phalanx.


I would like to contrast my observations of draft horses with laminitis to similar conditions in light horses. Laminitis carries a more guarded or unfavorable prognosis in draft horses for many reasons. Our ability to manage secondary problems is less satisfactory in draft horses. Size, when we consider a 1000-kg as opposed to a 400- to 500-kg horse, is the most important factor. Slings are seldom big enough, and hoists or hoist support systems may not be available to lift a draft horse safely. Locating a farrier who will work on a chronically lame draft horse and forge therapeutic shoes on a consistent basis is often difficult. Management of draft horses with myositis, decubital ulcers, infections, pneumonia, and other secondary complications is more difficult and costly. The owner must be informed clearly of cost, and a dedicated team (owner, farrier, and veterinarian) must be assembled to manage these complications. I generally tell clients that at least 1 year will pass before the horse’s level of function can be assessed reasonably.


Classification of laminitis is confusing, and I make little attempt to classify laminitis based on chronicity or by using the Obel grading system (see Chapter 34). Regardless of classification used, prognosis for return to function is poor if lameness is severe and persists for longer than 10 days with intensive treatment. In my experience, two major differences exist between draft horses and light horses. First, draft horses develop laminitis more frequently and severely in the hindlimbs. Second, draft horses are more likely to develop distal displacement (sinking) of the distal phalanx once laminitis occurs (Figure 125-2). This latter difference may be related to hoof quality or hoof care in general and the important role that body weight plays in causing distal displacement. In addition, shoeing methods that flair the hoof wall simply to give the impression of a large foot weaken laminar support. Distal displacement can occur in horses with traumatic laminitis without a traditional laminitic episode. Traumatic laminitis and sinking can occur unilaterally, only to then occur weeks to months later in the opposite foot. Traumatic laminitis caused by incorrect shoeing can be reduced greatly or eliminated when proper shoeing is provided on a regular basis.


image

Fig. 125-2 Lateromedial radiographic image of the front foot of a draft horse mare that had developed laminitis in all four limbs within 24 hours of foaling and retention of the placenta. The radiographic image was obtained 10 days after foaling. The proximal end of the radiodense marker on the dorsal hoof wall is at the level of the coronary band. Both extensive sinking and rotation of the distal phalanx have occurred. Note also the broad radiolucent line in the dorsal hoof wall, the result of laminar necrosis. The mare was managed until the foal was weaned, but humane destruction was ultimately necessary.


Diagnosis of laminitis is not difficult except in draft horses with traumatic laminitis that is slowly progressive, without an acute episode typically seen with laminitis in a light horse. These horses often have a dropped sole (including the frog in many horses), with the entire sole at a level below the hoof wall. Increased digital pulse amplitudes may be missed easily in a draft horse, but hoof tester sensitivity and abnormal stance are important clinical signs. Initial and follow-up radiographs should always be obtained.

Related posts:

  1. Lameness in Horses: Basic Facts Before Starting
  2. Thermography: Use in Equine Lameness
  3. Counterirritation
  4. The Carpal Canal and Carpal Synovial Sheath

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Jun 4, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Lameness in Draft Horses

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