The North American Thoroughbred

Chapter 106The North American Thoroughbred

Description of the Sport

King James I of England established horse racing as the Sport of Kings in the early seventeenth century, and the earliest English immigrants brought the sport to the American colonies. Colonials imported fine-blooded horses and staged informal race meets almost as soon as they hit land. Richard Nicolls took command of New Amsterdam, renamed New York, became the first governor of the colony in 1664, and established a racecourse.

Many of the founding fathers of the new country, including George Washington and Thomas Jefferson, raced horses. John Wickham, Aaron Burr’s attorney at his treason trial, lost one of the top American stallions of the emerging Thoroughbred (TB) breed, named Boston, in a card game in 1835. Nathaniel Rives won the difficult 2-year-old colt and ignored advice to geld him. Boston not only won 40 of 45 starts, but he also sired Lexington. A foal of 1850, Lexington became the top racehorse in the country by winning from New York to New Orleans.

Lexington was named for the Kentucky town that became the center of TB breeding. Horsemen quickly realized that healthy horses could be raised on the limestone base of Central Kentucky, and the horse Lexington helped establish the area by becoming the top sire in the United States for 16 years.

Racetracks sprang up in many cities, and although the industry suffered during the Civil War, Saratoga was the exception. The New York social elite took in the waters at the Spa to escape the heat and humidity of the city, attended the races during the day, and partied through the summer evenings in spite of the war. A few years after the conflict, Col. M. Lewis Clark founded the Louisville Jockey Club to conduct race meets in Kentucky. In 1875 the Louisville Jockey Club opened a new racetrack, later called Churchill Downs, and that year Aristides won the first edition of the Kentucky Derby (the Derby).

The Derby did not begin as America’s most famous race. Col. Matt Winn’s genius at marketing in the early twentieth century was required to create the legend the Derby has become. When the filly Regret won the race in 1915, the Derby rose to prominence quickly as a premier American sporting event and a major stop for 3-year-old TBs.

Fans were disappointed when owner Sam Riddle and trainer Louis Feustel deemed the Derby too early in the year for their strapping colt Man o’ War, the horse that had broken many records the previous year, winning 9 of 10 races. However, Man o’ War added to his reputation without the Derby, going through a perfect season of 11 wins in as many races. To many he remains the finest TB racehorse the United States has ever produced.

A new moral climate was sweeping the nation after the turn of the century. Gambling, including on horse racing, was banned in many states as a precursor to Prohibition, which began in 1919. Kentucky was the exception, and horsemen and racing fans found many ingenious ways to skirt the law. The need for more state revenue from the Great Depression in the 1930s prompted the ban on racehorse wagering to be lifted in many states. Until the 1970s horse racing was often the only legalized form of gambling in most states. From the 1930s to the 1960s horse racing, boxing, and baseball were the most popular sports in the United States.

War Admiral, sired by Man o’ War, gained such a following in the 1930s that the whole country listened to the Seabiscuit–War Admiral match race. Because the older Seabiscuit had lost his first 17 races as a 2-year-old, everyone expected War Admiral to win. Yet Seabiscuit, “the people’s horse,” beat War Admiral that day, and in 1938 Seabiscuit was said to have had more newspaper space than Hitler.

As a 3-year-old, War Admiral won the Derby, the Preakness, and the Belmont Stakes, races that became known as the Triple Crown. Only 11 horses have ever won all three races. In 1948 Citation so impressively captured the series that some thought the horse replaced Man o’ War as the greatest racehorse. That argument persisted for the next 25 years, despite the achievements of horses such as Native Dancer, Swaps, Kelso, and Dr. Fager, none of which won the Triple Crown. However, in 1973 a bright chestnut colt, Secretariat, so captured the public imagination when he won the Triple Crown that Time, Newsweek, and Sports Illustrated all put him on the cover. He won the image-mile Belmont Stakes by a spectacular 31 lengths.

Although the Triple Crown increased in stature, California developed a strong racing circuit. Santa Anita, east of Los Angeles, opened in 1934 and gained immediate attention by offering the then unheard-of sum of $100,000 (U.S.) for the inaugural Santa Anita Handicap. Across town, Hollywood Park began attracting movie stars and established its own fixture, the Hollywood Gold Cup. Bing Crosby and friends built Del Mar about 100 miles south.

As transportation by air became more popular in the last half of the 20th century, horses from the East and West began meeting regularly. In fact, Affirmed, the latest horse to win the Triple Crown, in 1978, prepared for racing at Santa Anita and Hollywood Park.

Regional rivalries became popular, which added to the success of the Breeders’ Cup series, inaugurated at Hollywood Park in 1984. Unlike the Triple Crown, which is solely for 3-year-olds, Breeders’ Cup Day offers races for various divisions. Two-year-olds show what might emerge at the next year’s Kentucky Derby. European horses often invade for the grass events and more recently have achieved notable success on synthetic surfaces. The Breeders’ Cup Classic attracts elite runners on the dirt from coast to coast and from abroad.

The Breeders’ Cup epitomizes the tenacity of the racing TB. Spectacular victories—including the triumph of Sunday Silence over archrival Easy Goer in the 1989 Classic, the victory of Personal Ensign over the Kentucky Derby–winning filly Winning Colors in the 1988 Distaff, and the devastating move Arazi made to capture the 1991 Juvenile after shipping to the United States from France—are legendary. American TBs regularly compete in Europe, Japan, Australia, and Dubai. Not even King James I could have envisioned the Sport of Kings developing into the international phenomenon it is today.

TB racing always has been an expensive sport. Since the introduction of pari-mutuel gambling, financial support and revenue have been derived from two groups: racehorse owners and the gambling public. The third leg of the horse racing industry is the racetrack operator. Racetracks are generally for-profit corporations, with the exception of Del Mar, Keeneland, Oak Tree at Santa Anita, and a few others. Racehorse ownership was once the domain of the wealthy, but now opportunities and partnership options are available for many. In the past, most owners maintained breeding operations to supply horses for their personal racing stables; commercial breeders were few. The focus of breeding was for successful racehorses, and rigorous selection for soundness was as important as racing ability. Commercial breeders have now become a major source of racehorses and have a different goal. They produce horses to satisfy the commercial market, an entirely different objective, often unrelated to producing a racehorse.

Commercial breeders offer horses at public auction, primarily as yearlings but also as weanlings and 2-year-olds in training. The auction market is fashionable and in many ways fickle and trendy. Buyers favor precocious yearlings, relatively more mature than others. Yearlings with sprinting bloodlines and well-muscled yearlings sell better than those with a classic distance pedigree and conformation for all but the most expensive horses. Little is known of soundness of the sire and dam. Although these trends are worrisome, one positive consequence has been the ever-improving quality of horse offered at public auctions. Now some of the best-pedigreed horses in the world are sold at public auction, a fact not true 30 years ago, and even traditional owners and breeders have entered the lucrative commercial market.

The commercial market is a straightforward avenue for owners to buy a high-quality racehorse without maintaining broodmares. The September Keeneland yearling sale offers nearly 5000 yearlings over a 10-day period. Numerous other sales are conducted throughout the year. Presale examination is an important part of veterinary practice at racetracks (see Chapter 99). The auction environment can be an extremely high-pressure setting for the veterinarian because the knockdown price may reach millions of dollars.

Owners can also buy horses in claiming races. In claiming races the prospective owner buys the horse for a predetermined price before the race, and the horse is considered sold once the starting gate opens, regardless of whether the horse wins or even finishes the race. Purses and monies from purchase (claim) go to the previous owner. Potential buyers of claiming horses cannot examine the horse, but they can watch it walk into the saddling paddock. Buying a horse by claiming gives an owner a ready-made racehorse, whereas owners and breeders have to wait at least 3 years before racing a homebred horse, and yearling buyers have to wait at least a year. Unfortunately, the risks in claiming are considerable, because the claiming game has no honor and the new horse may already be at the end of its career.

Racetrack operators have changed to meet demands of the racing fans. The state, racetrack operator, and horsemen, through purse distributions, obtain income from a percentage of the moneys wagered, called handle. Revenue from simulcasting races across the United States and internationally is now an important source of handle, and Internet and at-home wagering are already realities. There was a time in the 1970s when Santa Anita and Hollywood Park had a higher daily average attendance than the Los Angeles Dodgers baseball stadium. On-the-track attendance has dwindled and contributes only a fraction to purses and commissions compared with what it did 40 years ago, when a fan had to come to the track to place a wager. Unfortunately, for reasons the racing industry is now regretting, the revenue sharing from off-track sites is much less than when the same amount of money is wagered on-track. The amount of revenue generated for purses and racetrack operators has not kept up with inflation, thereby placing greater economic stress on all industry participants. The importance of simulcasting to the future of horse racing has led to consolidation of racetrack ownership.

Because track operators emphasize handle, races are run in a manner to encourage betting. Races must be competitive, and the more horses the better. An anathema to the nongambling race fan and many horsemen is that gamblers bet more money on a large field of poor-quality horses than on a small field of high-quality horses. In the United States, field size rarely exceeds 12 horses, because dirt racetracks are relatively narrow and have tight turns, and turf courses, usually inside of the main dirt track, are even narrower with tighter turns.

Races are made to be competitive by restricting which horses are eligible to run in a particular race. Most important are age, gender, distance, and surface (turf or dirt). Sex and age restrictions limit which horses are allowed to compete in a race. Age is a major factor, and 2-year-olds are never raced against older horses, because they would not be competitive. Distaff races are those restricted to fillies and mares, and although the distaff side is not excluded from open races, such races are seldom competitive, except early in the 2-year-old year.

Distance and surface are conditions selected to suit the horse. Another set of conditions, handicaps and allowances, can be confusing but works well. Handicap and allowance races are set up to even the race by varying the weight carried by the horse. Weight variation is a subjective value, determined by racing officials for handicap races. In allowance races, weight variation is determined by a set of published criteria. For example, 3-year-olds carry less weight than older horses, fillies less than colts, and nonwinners may get additional weight off.

Most races in the United States are claiming races. In claiming races, horses of similar ability are pitted together. Because of the risk of losing a horse by claim, owners and trainers are discouraged from running more valuable horses to steal a purse. The claiming aspect of American racing is popular, but it has several negative effects on racing.

Stakes races are for the best horses. Stakes races require an entry fee and some require an additional starting fee. Stakes races are raced according to sex, age, distance, and surface. Stakes races are graded, listed, or restricted. Restricted stakes races, popular in recent years, restrict eligibility to the state of foaling or to conditions similar to allowance races. Stakes races are run even if only one horse is entered, but this is rare and is called a walkover. Stakes can be handicaps, allowances, or weight-for-age races. In weight-for-age races all horses carry the same weight, except for the well-established allowances for age and gender. The Kentucky Derby is a weight-for-age race for 3-year-olds. All horses are assigned the same weight (126 lb [57.3 kg]), but a filly receives a weight allowance and carries 123 lb (55.9 kg). The best stakes races are graded by a national committee and classified as Grade 1, Grade 2, or Grade 3; Grade 1 races are the top races. The Kentucky Derby and Breeders’ Cup Classic are examples of Grade 1 races. The North American graded stakes races are analogous to the European group or pattern races.

Nonstakes races fall into several categories. Maiden races are for horses that have never won a race and can be allowance or claiming races. Races can be restricted to horses that have not won a certain number of lifetime starts. Other specific conditions for races can include eligibility for horses that have not won a race in a certain time period or over a certain distance. Claiming races also are restricted by age, gender, distance, and surface. Although races are devised to maximize competitiveness, the uncertain offering of races for nonstakes horses greatly complicates training and veterinary care, because timing for future races can be difficult to judge.

Stakes races are predominantly for horses 2 and 3 years of age, whereas horses may continue to race in claiming races up to 10 to 12 years of age. Claiming horses may drop progressively in class and value, and the lowest level of TB racing in the United States is considerably below that of the United Kingdom. Much of the following discussion reflects our dealings with high-quality, younger horses. These situations are easier for the veterinarian to be in control and to dictate the diagnostic approach and therapeutic plan, working with the trainer. With low-value claiming horses the trainer is more likely to dictate what is treated and with what. Frequently joints are treated with corticosteroids alone, rather than in combination with hyaluronan. Regardless of level of competition, it is important to establish and maintain a good owner-trainer-veterinarian relationship. This helps ensure the health of the racehorse and the success of the racing venture (JAB).

Track Surface and Lameness

Track surface is an important factor in the development of lameness and frequently is overlooked or neglected in lameness discussions (PJM, MWC) (see Chapter 105). Track surface dictates frequency and type of lameness. Injuries are often blamed on track surfaces, but musculoskeletal injuries are multifactorial. Shoeing, medication, training patterns, commercial breeding, and many other factors have all been implicated in the high injury rates in race-horses, and as often as not injuries cannot be fairly blamed on track surface (RMA, JAB). The most important factor in fatal racing injuries is not the track surface, but the horse (RMA). Almost all horses that develop fatal musculoskeletal racing and training injuries have evidence of preexisting pathology at the site of the fatal injury. They are repetitive stress injuries. Regardless, track surfaces play an important part in injury development, and the veterinarian needs to appreciate the types of injuries that are likely to develop in the track surfaces in his or her practice area.

Surfaces that favor speed also predispose horses to catastrophic breakdowns. Quality of racing surface is much more important than whether the surface is dirt or turf. Hard racetracks with little cushion are the worst surfaces. One of us (MWC) observed 38 horses with bone injury in a 4-week period when horses were training and racing on a hard racetrack. When sand was added to the track and the cushion increased from 6 to 11 cm, over the ensuing 4-week period only four horses developed bone injury. However, race times increased substantially. Horses need not train on hard surfaces to be able to race on them. Training on a forgiving surface then racing on a fast surface is safer than the opposite approach or working on a hard surface constantly. Consistent and uniform surfaces are the safest, allowing horses to remain sound and reducing incidence of injury (JAB). Track surfaces can change dramatically, especially in inclement weather.

Banking around turns can influence how horses negotiate turns and lameness distribution and expression. The hindlimbs of horses negotiating flat turns appear to slip out from under them, and in some instances horses nearly go down.

Track surface can make a difference in how horses with injuries are managed or rehabilitated. Horses rehabilitating after fractures or other bone injuries should not train on hard tracks. Likewise, horses coming back after soft tissue injuries or racing with minor infirmities should not be trained on deep or muddy tracks.

Many European horses that previously trained on grass now race in North America. Most race and continue to train on grass, but some make the switch to training and racing on dirt successfully (see Chapter 107). Our impression is that European horses appear to have fewer forelimb and more hindlimb lameness problems than North American TBs. European horses often train on long straightaways, and this, combined with a forgiving surface (grass), is a situation different from training on dirt in North America. Horses bred to race on the turf appear to have an inherent conformational difference that allows superior performance on grass. Synthetic racing surfaces fall somewhere between dirt and turf relative to horse surface preferences. Turf horses are much more likely to be competitive on synthetic surface, even if they do not handle dirt tracks. Just as there are horses that do well or poorly on dirt or turf, there are horses that handle synthetic surfaces well and horses that do not.

In recent years more attention has been placed on track surfaces than ever before. The major change has been the introduction of synthetic surfaces in North America. The first Breeders’ Cup events run over a synthetic surface were at Oak Tree at Santa Anita in 2008 and 2009. Synthetic surfaces are primarily sand, some fiber material, and a wax or polymer used to coat the sand and bind the material together. Unlike dirt tracks, which are usually cambered to drain horizontally, synthetic tracks are designed to drain vertically and require a drainage system built into the track. The racing results from synthetic surfaces have been mixed. In California, where the racing commission mandated synthetic surfaces by the beginning of 2008, racing fatalities dropped 40% when main track racing fatalities were compared with the same main tracks when they were dirt from 2004 to 2007. The training fatalities at the same tracks have not significantly improved with the synthetic surfaces. The distribution of racing and training injuries resulting in fatalities has changed. There are many more hindlimb injuries with synthetic surfaces compared with dirt (RMA). There are also numerous reports of increases in soft tissue injuries, primarily involving the proximal aspect of the suspensory ligament (SL). Although synthetic surfaces appear promising, the technology is relatively new, and the synthetic surfaces have had installation and maintenance problems.

A better understanding of the relationship between track surfaces and injury has been woefully neglected in the past. A number of research efforts have begun to better characterize the important relationship between track surfaces, biomechanics, and ultimately injuries. A safe racing surface has become of paramount importance to racing as the highly public injuries to Barbaro in the 2006 Preakness and Eight Belles in the 2008 Kentucky Derby have made equine welfare concerns a public debate. Marketing surveys by the racing industry have shown racing fatalities are of major concern to the general public. There can only be increasing emphasis on equine safety in the future.

Medication and Drug Testing Considerations

Horse racing has always regulated the use of medications, but more recently the relatively permissive North American medication regulatory scheme has come under greater scrutiny. Outside North America most racing jurisdictions operate under International Federation of Horseracing Authorities (IFHA) rules. IFHA rules prohibit the use of nonsteroidal antiinflammatory drugs (NSAIDs) within several days of racing, whereas all North American racing jurisdictions allow some use of at least one NSAID the day before racing. Whether the permissive NSAID regulations and other medication policies contribute to the higher racing fatality rates in North America than most other racing jurisdictions using IFHA rules is debatable. Further complicating the issue, racing regulatory veterinarians, the veterinarians responsible for the prerace examinations have begun to question whether North American NSAID regulations are compromising their examinations by masking clinical signs of inflammation. Currently, an approximate 4-mg/kg dose of phenylbutazone about 24 hours before racing is permitted in North America and conforms to the blood level of lower than 5 mcg/mL on raceday.

The policies and regulations governing the use of corticosteroids, particularly intraarticular corticosteroids, are also under scrutiny. Most racetrack veterinarians believe intraarticular corticosteroids are most effective if used 5 to 10 days before racing (RMA, JAB). Unfortunately, changes in the way races are carded today have made planning for races problematic except for stakes races. Trainers cannot confidently plan for races on a certain date and feel forced to wait until the horse is in a race to perform intraarticular injections, sometimes as little as 2 days before the a race. The American Association of Equine Practitioners is recommending that racehorses should not receive intraarticular corticosteroid injection within 5 days of racing. Racing regulatory veterinarians have called for an outright prohibition within 5 to 7 days of racing (RMA). Most corticosteroids are Association of Racing Commissioners International (ARCI) Class 4 drugs, and recent research efforts have been directed toward increasing the sensitivity of drug screening for corticosteroids. Research suggests triamcinolone acetonide and betamethasone have chondroprotective properties when used prudently. On the other hand, one of the most commonly used intraarticular corticosteroids, methylprednisolone acetate, does not fare as well in laboratory studies but is still a preferred intraarticular corticosteroid of many racetrack practitioners because of potency and consistency of clinical response. The pharmacodynamics of intraarticular corticosteroids is just now being studied in horses. With a better understanding of the clinical response to these drugs, combined with advances in laboratory detectability, the way corticosteroids are used may change dramatically within a few years.

Withdrawal time information is not readily available in all jurisdictions for many common therapeutic drugs used for equine lameness. The state-by-state regulation of racing in the United States and the large number of drug-testing laboratories complicates racetrack veterinary practice. Prudence dictates that all veterinarians treating horses intended to race at state-sanctioned racetracks be familiar with the drug testing and medication regulations in that jurisdiction. Resources that may be of use to racetrack veterinarians are the ARCI and the Racing Medication and Testing Consortium (RMTC). Both organizations have websites with information on medication and veterinary practice regulations as well as drug testing.

Lameness Examination

A racetrack clinician has distinct advantages over other practitioners. A racetrack veterinarian is involved intimately in the day-to-day operation of a racing stable and becomes familiar with the normal gait, disposition, and general health care factors of each horse, such as appetite, coat condition, weight, training and racing status, and performance. Numerous examinations can be performed easily if needed. Horses can be examined before and after training to see if lameness worsens or improves.


The most important piece of information is the training history. What did the horse do today, yesterday, and the day before? How far is the horse from racing? When was the last fast work or race? Did any problems occur? Did the horse want to train? Did the horse lug in or out? Did the horse cool out normally? When did the trainer or exercise rider notice a problem? When was the last time the horse was shod? Is the horse receiving any medication? NSAIDs and corticosteroids can easily compromise the veterinarian’s ability to properly evaluate lameness (RMA, JAB). The entire veterinary medical history is important for the veterinarian to know, but the past medical history of claiming horses is usually unavailable.

Most fractures occur in horses with a history of a recent hard workout or race. Sometimes lameness may not become apparent until the horse returns to the track several days later, but the injury occurred in the previous workout or race. Humeral stress fractures are the exception, because they usually occur in horses returning to work after not having worked for 45 to 90 days. Horses that lug in (drift toward the inside rail) or lug out (drift toward the outside rail) usually are moving away from the source of pain, but not always. The gallop is a complicated gait, and some horses may drift toward the side of pain while galloping at high speed, perhaps reflecting the lack of power on the affected side (MWR). Most horses in North America finish a race on the right lead. Finishing a race on the left lead may be normal for a horse, but in some horses finishing on the left lead may be a sign of high-speed lameness. A left-lead finish should prompt careful investigation of the left forelimb and right hindlimb as potential sites of lameness (MWR). Many lameness conditions are insidious in onset. Subtle signs, such as a horse that is unusually nervous and prefers to break into the gallop instead of jogging, are easy to overlook. Lameness the day after a shoeing change may implicate a close nail or a drastic change in hoof angle.

The age of the horse is important. Dorsal third metacarpal bone (McIII) disease and other stress-related bone injuries are unusual to diagnose in older horses if they do not have problems at 2 or 3 years of age. Older claiming horses are much more likely to have chronic osteoarthritis (OA), osteochondral fragmentation, or tendon injuries.


The physical examination should be routine and complete. Horses are first examined in the stall, where they are comfortable and are more willing to tolerate manipulation. One of us (PJM) feels strongly enough about thorough examination that if trainers want to start with a visual examination while horses are tacked up and proceed directly to injection, they should find another veterinarian. Many lameness conditions are acute, and signs of inflammation are clearly useful. Horses with chronic lameness can be challenging, but long-term association with a horse is of great benefit. Regardless, the examination is the same. Palpation is critically important in evaluating racehorses, possibly the single most important clinical skill a racetrack veterinarian can develop. Very subtle abnormalities or changes from previous examinations can often be the key to developing the most effective diagnostic plan (JAB). With the horse standing squarely, all limbs are palpated for heat, pain, and swelling. During individual flexion of the front fetlock joints and carpi, pain response is important. Pain during carpal flexion almost always indicates a problem in that region. The clinician should remember that during lower limb flexion tests, joints other than the fetlock are being stressed. If concerned, we flex joints independently if possible. Whenever a pain response is elicited, the same palpation technique should be used to compare the response with that of the contralateral limb. There is considerable individual variation from one horse to another, particularly with more subtle responses. All aspects of the PSBs should be examined with the limb in flexion. SL branches, body, and origin and digital flexor tendons are carefully palpated along the entire length. The dorsal aspect of the McIII is palpated by placing the palm of the hand around the tendons and applying firm finger pressure. The forelimb is then brought forward while elevated, and the dorsal cortex of the McIII is palpated with firm thumb pressure. Careful palpation of the dorsal and palmar aspects of the McIII is important in detecting fracture of this bone (MWC).With the palm of the hand on the dorsal aspect of the McIII, the fingers can be used to palpate the proximal aspect of the SL and each splint bone. Care must be taken when examining the dorsal and palmar metacarpal regions, because the clinician may inadvertently cause pain on the dorsal cortex by examining the palmar aspect of the metacarpal region and vice versa (PJM). Proximal palmar metacarpal pain is important to detect, but false-positive results can occur (MWC). Any suspicious response should be evaluated further with ultrasonography (PJM). The carpus is flexed and the dorsal surfaces of the antebrachiocarpal and middle carpal joints are palpated with thumb pressure. An effort should be made to stretch the joint capsule around the borders of each carpal bone, because stretching often elicits pain if a lesion is present. To evaluate the elbow and shoulder regions, the limb is pulled backward and forward. With the limb extended, a jerking, upward motion sometimes causes pain in horses with humeral stress fractures. The shoulder joint and intertubercular (bicipital) bursa should be palpated with firm digital pressure.

The hands should be run lightly over the back to assess for sore or tense muscles. The lumbar and sacroiliac regions, gluteal muscles, and greater trochanter of the femur should be palpated from each side. Although the process appears hazardous, the gluteal muscles and greater trochanter also should be palpated from behind. If necessary a forelimb can be elevated. Firm pressure should be used to detect gluteal myositis or trochanteric bursitis. Standing behind the horse is the best way to compare effusion of the femoropatellar joints. Each hindlimb should be examined in the standing and flexed positions. The Churchill test should be performed bilaterally (see Chapter 6). A positive response suggests distal hock joint pain. Negative findings on palpation and manipulation do not eliminate a joint from consideration, but positive findings often point to the source of pain causing lameness.


It is mandatory to observe the horse during the first few steps out of the stall. Then the horse is usually walked down the shed row and back. Occasionally the horse is trotted immediately. If a horse appears “stiff” initially, it is useful to walk the horse a couple of times around the shed row to help discern if the lameness is real or if mild stiffness is a normal characteristic of that horse. This is important with older horses that may have chronic problems. Horses with painful conditions do not generally warm out of lameness (JAB). It is important to trot the horse at a comfortable speed for the horse, not the handler, and the horse must be trotted far enough to reach an even speed. The head must be free, without allowing the horse to throw the head. Surface is important, and the harder, the better; soft surfaces may hide lameness. The horse is trotted in a straight line and while circling. Trotting the horse in a circle is the best way to differentiate diagonal or ipsilateral lameness (i.e., left forelimb from right or left hindlimb) and exacerbates many lameness conditions. Horses with tibial stress fractures are much worse while circling. Horses with third carpal bone pain and medial foot lameness are worse with the affected limb on the outside of a circle. Horses with lameness of the fetlock joint are usually worse with the affected limb innermost. Although characteristics of lameness while trotting are important, they are subjective.

At times, observing a horse under tack is useful. Often horses with hindlimb lameness are best examined on the racetrack, because many horses do not use themselves behind. Only when horses are absolutely sound in hand is examination at speed warranted, and even then, with the exception of understanding the complaint of the rider, obtaining useful diagnostic information is rare. However, one of us (PJM) likes to examine horses with obscure lameness on the track, under tack at the trot.

The usefulness of flexion or other manipulative tests is debatable. Lameness may be exacerbated, but disagreement exists over what a positive response means. For instance, when performing fetlock flexion, a positive response is common even in horses with lameness unrelated to the fetlock joint (RMA). One of us (PJM) finds fetlock and lower limb flexion tests worthwhile, but not carpal flexion, and finds hindlimb flexion tests nonspecific. One of us (MWC) finds forelimb flexion tests useful but finds all but the lower limb flexion test in the hindlimbs questionable. Finally, one of us finds the carpal flexion test the most specific and accurate flexion test; horses with a positive response generally have carpal region pain, and there are few false-positive results (MWR; see Chapter 8). Hindlimb flexion tests lack specificity (MWR). Each clinician needs to develop a protocol and be consistent.

Jun 4, 2016 | Posted by in EQUINE MEDICINE | Comments Off on The North American Thoroughbred

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