THE ATHLETIC HORSE

The equine athlete, like its human counterpart, achieves speed, strength and grace through physical exercise.

Horses, like humans, excel at different sports based on physical and emotional attributes. Thoroughbreds are ideally suited to middle-distance racing, easily covering distances of three-quarters of a mile to 1 1/2 miles. In contrast, Quarter Horses and other stock horse breeds are much more heavily muscled and short-coupled. They are unequalled at distances from 220 to 660 yards and are ideally suited for aggressive athletic events such as cutting, roping and reining -- sports that require tremendous strength and agility. Arabians and their crosses excel in long-distance races in which the horse covers 25-100 miles in one day.

The average Thoroughbred in racing condition weighs approximately 1,000 pounds, and stands 15.0-17.0 hand high (60 to 68 inches) at the shoulder (withers). (See diagrams) It is the fastest breed of horse over middle distances. A galloping Thoroughbred can cover 20 feet or more in a single stride and achieve speeds exceeding 40 m.p.h. Though a horse's leg structure appears slender and fragile, the bones are extremely strong and well-reinforced with tendons, ligaments and skin. At the point in a horse's galloping stride, where it carries itself forward on one front leg, a force greater than 2,000 pounds is exerted on the column of bones.

GAITS

A gait is a characteristic limb coordination pattern used in locomotion. Horses perform a variety of gaits that are distinguished by the sequence and timing of the limb movements. The walk, trot, canter and gallop are distinguished by their speed, rhythm and footfall placement. A horse's walk is a four-beat gait, wherein each foot rises and falls independently. The trot is a two-beat gait, where diagonal front and rear legs rise and fall synchronously. The canter and gallop look similar although the canter is a three-beat, slower version of the gallop. The gallop is a faster, more extended version of the canter, with a four-beat rhythm, whereby each foot hits the ground separately.

Gaits are classified as symmetrical or asymmetrical. In symmetrical gaits (walk and trot) the left and right footfalls are equally spaced. In asymmetrical gaits (canter and gallop) the left and right footfalls occur as couplets and the steps are of unequal distance with one front leg and one hind leg extending further ahead than the other front and hind leg. The leg that takes a longer step is called the leading leg and the opposite leg is the trailing leg. (See diagrams)

When the horse approaches the left-handed turns found at North American racetracks, it will take the left lead to balance itself throughout the turn. In a straightaway, the horses usually switches to a right lead to avoid fatigue. Different stresses are placed on the leading and trailing legs, which affects the type of injuries occurring in the right and left limbs in turns and straightaways.

MUSCULOSKELETAL SYSTEM

Consisting of the bones, muscles, ligaments, tendons and joints of the head, vertebral column and limbs, together with the associated muscles, tendons, ligaments and joints. Its primary functions are to support the body, provide a system of levers for locomotion and in some instances to provide protection to certain vital structures, e.g., the brain, eyes, and viscera. (See diagrams)

A joint occurs where two or more bones meet. There are different types of joints, the most important being the synovial joint, in which the ends of the bones are covered with a layer of smooth articular cartilage and the joint surfaces are lubricated by an oily synovial fluid produced by the joint capsule. Muscle fatigue, which occurs at the end of a workout or race, can cause a loss of rhythm leading to lameness as the horse compensates for the fatigue.

A horse does not have muscles below the knee (front) or hock (rear). In that area, the major tendons and ligaments are the suspensory ligament, superficial and deep flexor tendons, and superior and inferior check ligaments. JOINT INJURIES: Injuries to joints are one of the most common lameness problems treated by the racetrack veterinarian. The most common injuries are bone chips (intra-articular chip fractures) in the knee (carpus) and ankle (fetlock) joint or inflammation of the synovial membrane and joint capsule (synovitis and capsulitis). When there are small fragments of articular cartilage and bone in the joint, they cause irritation to the synovial membrane and clinically appear the same as synovitis and capsulitis. A specific diagnosis is usually made after viewing radiographs (x-ray film).

Cases of synovitis and capsulitis can be treated with intra-articular injections of therapeutic medications. The careful use of the right corticosteroid in the right dose can be effective and safe. Other drugs that are used for the treatment of inflammation in these joints include hyaluronic acid and Adequan (polysulfated glycosaminoglycans). While synovitis and capsulitis are most commonly recognized in the knee and ankle, they also commonly occur in the coffin joint and the distal hock joint.

Bone chips are often best treated by removal by arthroscopic surgery. In the case of the treatment of fractures in the joint or injuries to the cartilage, the goal of treatment is to restore the articular surface and minimize the development of degenerative changes in the articular cartilage, a condition known as degenerative joint disease (DJD) or osteoarthritis. Osteoarthritis is the consequence of either an injury that is too severe or chronic. Osteoarthritis is a permanent form of arthritis with progressive loss of articular cartilage in a joint, commonly leading to a horse's retirement.

MUSCULAR INJURIES: The two most common muscular problems in racehorses are "tying up" (acute rhabdomyolysis) and back pain due to repetitive strain. Tying up, a cramp affecting the entire body, is a common condition and the cause of the disease is still poorly understood. The problem will usually develop at levels of exercise below the anaerobic threshold. It is clear that some animals have a psychological or biochemical propensity to tie up in that they perhaps lack certain enzymes involved in energy metabolism. When tying up occurs, it is treated with anti-inflammatory drugs, tranquilization and IV fluids when appropriate.

"Back soreness" is a rather nebulous condition. It is usually muscular in origin, as opposed to humans where it is commonly associated with the intervertebral joints and the intervertebral disk. Back soreness is often secondary to hind or front limb lameness; the horse changes its way of going to compensate for a problem in its limbs and back soreness occurs as a consequence.

FRACTURES: Smaller fractures can be effectively treated by removing the fracture fragment or by screw fixation, in which screws are surgically inserted into the bone to hold the fragments together. In such cases, the horse will often be able to return to athletic function. More severe fractures, such as to the distal condyle (lower knobby portion) of the cannon bone and the first phalanx (long pastern bone), can also be successfully treated with screw fixation. Other severe injuries that can be treated with screw fixation include slab fractures, where the bone is broken vertically and extends from one articular surface to another in the knee (carpus) and hock. Fractures in the shafts of the long bones (bones not within joints), however, require more sophisticated repair techniques using bone plates as well as screws. In the last 15 years, the development of new equipment and implants has enabled veterinarians to repair many fractures that were previously considered hopeless.

Fractures in the upper limb are problematical in that the horse needs to stand on the limb immediately after anesthesia and external support with a cast may be inadequate to support its weight. Horses are physiologically designed to run. Their internal organs, including digestive and circulatory systems, are dependent on the animal's ability to move. In the case of younger animals (under 600 lbs.), fractures to the upper bones in the body can often be successfully repaired.

Bone grafts are also sometimes used to help repair of fractures. Bone is taken from another area of the horse's body (often the hip) and implanted in the area being repaired to hasten the repair process.

There are still situations when a horse with a serious fracture cannot be saved. The fracture site might be too contaminated or blood supply may be sufficiently compromised to allow for successful repairs. The horse's large size and weight often inhibit treatment. Sometimes an individual's temperament won't allow for recuperation. Many times, complications occur in the other limbs due to excessive weight-bearing during the rehabilitation period. In these cases, the humane solution is euthanasia.

A common injury site in the lower limb of Thoroughbreds are the proximal sesamoid bones. Located at the back of the fetlock joint the sesamoid bones act as a lever over which tendons and ligaments pass. The suspensory ligament has an extensive attachment to the outer edge of the sesamoid bones. There are four main types of fractures in the sesamoids: apical (along the top of the bone), abaxial (the side of the sesamoid away from the ankle joint), mid-body (sesamoid broken in half) and basilar (through the bottom). The fracture of the bone itself is not always the major determinant of the horse's future. The amount of soft tissue damage, disruption in blood supply and damage to the suspensory ligament's attachment to the bone are important factors in the prognosis. The more severe the damage to the ligaments, the less support there is for the limb, therefore, the more critical the injury. Surgical removal of small sesamoid fragments can commonly result in a sound racehorse.

SUSPENSORY APPARATUS: This consists of the suspensory ligament, sesamoid bones and distal sesamoidean ligaments. These structures together make up the support for the limb below the knee or hock. The suspensory ligament inserts at the top of the cannon bone and passes down and is attached to the sesamoid bones. The distal sesamoidean ligaments attach to the bottom of the sesamoid bones and pass down and attach to the long and short pastern bones. (

A traumatic disruption of any of these structures (rupture) of the ligaments or fracture of both sesamoid bones will take away the support of the lower limb and loss of integrity of the fetlock joint. This disruption is the most common cause of severe breakdown on the racetrack.

HOOF: The hoof is made up of several structures, primarily the coronary band (where the hair meets the hoof), hoof wall, insensitive laminae (layer just under the wall of the hoof), sensitive laminae (internal part of the hoof), frog and sole. (See diagrams) The hoof wall -- the outer covering of the hoof -- is comparable to the human fingernail; it grows yet it has no nerve endings. Underneath the insensitive laminae are the sensitive laminae, which have nerves and carry blood to warm the foot and nourish its growing tissues. The area between the insensitive and sensitive laminae is called the "white line." The hoof wall is supple; when a horse puts weight on a hoof, the hoof wall expands slightly as it becomes weight-bearing and contracts when the weight is lifted.

The hoof wall grows downward at a rate of about 1/4-inch a month. The hoof wall is trimmed by a farrier to maintain the balance of the foot and to optimize stress on the bones, ligaments and tendons of the leg. Therapeutic trimming and shoeing are sometimes used following an injury to reduce stress in a particular area. Some conformational faults can be helped by corrective trimming if it is performed early enough in the horse's life.

The weight of the horse is transmitted through the two layers of laminae to the third phalanx or coffin bone, which is similar in shape to the hoof wall. On the undersurface of the hoof is a V-shaped structure called the frog. (See diagrams) The frog is easily seen when the horse's hoof is picked up; the point of the V-shape is toward the toe and the two legs of the V lie near the horse's heel. The soft, elastic qualities of the frog allow it to absorb shock and store moisture for the rest of the hoof.

The sole is a tough covering that protects the sensitive structures inside the hoof from injury. Not intended as a weight-bearing structure, the sole is more or less concave.

RESPIRATORY SYSTEM

The primary function of the respiratory system is gas exchange. Air is conducted from the nostrils through the nasal passages, pharynx, larynx and trachea to the lungs. Air contains 21 percent oxygen, which diffuses from the air sacs (alveoli) of the lung into the pulmonary capillary circulation where it is picked up by the hemoglobin and transported via the circulatory system to the muscles. The muscles use oxygen to burn fuels (carbohydrates and fats) to produce the energy necessary for work, with carbon dioxide being a by-product. The energy is utilized for muscle contraction and the carbon dioxide is exhaled. The horse must breathe at a respiratory rate sufficient to satisfy the body's oxygen needs. If the needs are not met the horse is in an oxygen deficit. All horses are in an oxygen deficit at the end of a race. The amount of oxygen required is directly correlated to the intensity and duration of the exercise (speed and distance). The amount of air breathed over a period of time is a product of the respiratory rate and the volume of each breath (tidal volume). The respiratory rate for the horse at a gallop is linked to stride frequency at a one-to-one ratio with the horse exhaling when the lead limb strikes the ground. For a horse running at maximum speed, the respiratory rate can reach 150 breaths per minute (2.5 breaths per second) and the tidal volume can exceed 12 liters per breath. The total amount of air entering the horse's lungs while racing is approximately 1,800 liters per minute (about 475 gallons of air).

Anatomically and physiologically, the horse's respiratory tract is divided into the upper and lower respiratory tracts. The upper respiratory tract includes the nostrils, nasal passages, pharynx, larynx and trachea. The upper respiratory tract warms, humidifies and filters the air on its way to the lungs. The lower respiratory tract includes the structures that lie within the chest (thorax), primarily the lungs. (See diagrams)

The upper respiratory tract has little margin for error to accommodate the high flow rates through the relatively narrow opening of the larynx. For the running horse with its head down and nose extended, the pathway for the air approximates a straight pathway to the lungs if all structures function normally (see diagrams) Horses are unusual in that they must breathe through the nose, unlike other domesticated species that have the option of breathing either through the nose or mouth. This physiological characteristic is termed an obligate nasal breather.

Horses are subject to many of the same lower respiratory diseases as humans. Horses can develop either allergic or infectious bronchitis, pneumonia, pleuritis, and pleuropneumonia. Treatment for these diseases is similar to that for humans with the same conditions. Pneumonia, pleuritis and pleuropneumonia are particularly serious illnesses of the horse. Historically they were most often associated with long-distance shipments of horses, hence the term "shipping fever."

EXERCISE-INDUCED PULMONARY HEMORRHAGE: This occupational disease is the major lower respiratory problem of racehorses. Horses with EIPH bleed from the lungs during intensive exercise. Usually the hemorrhage is minor but can at times be profuse. Fatalities are extremely rare. The cause of EIPH is unclear but several factors are evident. There is a definite relationship between the small airway disease (bronchitis), alterations in the vasculature of the lung in the dorsal-caudal (upper back) tip of the lung field, and EIPH.

EIPH is a new description for an old disease with a long history in Thoroughbred racing. The great grandsire of Eclipse, the pre-eminent Thoroughbred sire, had his name changed from Bleeding Childers to Bartlett's Childers lest the infirmity which prevented him from racing compromised his acceptability at stud. The introduction of a relatively new medical instrument, the fiber optic endoscope, to equine veterinary practice in the early 1970s allowed the safe and effective visualization of the upper respiratory tract of horses for the first time. With the fiber optic endoscope, veterinarians could determine that the blood observed in the trachea (upper respiratory system) actually originated from the lungs (lower respiratory system). Until that discovery, the condition was termed epistaxis (nosebleed) and the hemorrhage was thought to originate somewhere in the head. Less than one horse in 20 that has EIPH has blood at the nostrils. University studies indicate a significant percentage of racehorses, as high as 85 percent in one study, experience EIPH to some degree at one time or another. There are no indications to suggest that the incidence of EIPH has increased in recent times as the incidence of epistaxis has remained essentially constant over the last century. Only the diagnostic capabilities have improved.

The most common treatment for EIPH is the administration of furosemide (trade name Lasix) as a preventive treatment for EIPH. Furosemide is the only therapy for EIPH which has been shown to reduce hemorrhage under breezing and racing conditions. Racing jurisdictions that allow the use of furosemide limit the administration to three or four hours prior to racing to avoid any dilution effect which may complicate post-race drug testing of the urine. Contrary to common misconceptions, furosemide does not affect the drug-testing procedure when used in the prescribed manner (four hours previous to the race).

DIGESTIVE SYSTEM

Over millions of years, horses have evolved specialized digestive tracts adapted to utilize diets containing high quantities of plant fiber. Horses are grazing animals with digestive systems designed for constant plant-food intake. The entire digestive system in a mature horse is a 100-foot-long continuous tract that begins with the mouth and ends with the rectum. The digestive organs include a small, simple stomach followed by a long, narrow small intestine. The stomach and small intestine are where most of the protein, fat, vitamins and minerals that are contained in feed are digested and absorbed. After the small intestine are two very large organs, the cecum and the colon, known collectively as the large intestine or hindgut. This is where fiber digestion occurs. The large intestine of the horse holds about 21 to 24 gallons of liquid and houses billions of bacteria and protozoa, which produce enzymes that break down (ferment) plant fiber.

COLIC: The leading cause of death in horses, colic refers to abdominal pain. The discomfort can be caused by a simple obstruction, usually in the large colon; a strangulation, usually a twist or torsion in the small or large intestine that shuts off the food passageway and blocks the blood supply; abnormalities of the intestinal blood supply (vasculature), usually caused by parasites (i.e., strongyle larvae in the blood supply); and other disorders that include gastric ulcers. Early symptoms include sweating, expressed discomfort and pawing the ground. Horses with severe symptoms of colic will roll or throw themselves to the ground. Because horses cannot normally regurgitate, anything that is in the stomach or small intestine has to pass through the entire digestive tract before being eliminated.

Early treatment of colic often includes sedatives, analgesics and oiling the horse, in which the veterinarian administers mineral oil directly into the horse's stomach via a nasogastric tube to assist in passing an obstruction or to relieve excessive gas. An antifermentative might be prescribed to reduce gas. Surgical intervention is sometimes necessary to remove an impaction or fix a twist or other abnormality in the intestines. Horses can have many feet of their intestine removed and still have a normally functioning digestive tract.

It is not possible to prevent all colics but the incidence can be reduced through proper management, including a good parasite control (deworming) program, providing the horse with plenty of fiber and increasing feeding frequency.

LICENSED PRACTITIONERS

An equine practitioner is a graduate, licensed veterinarian who devotes the greatest portion of his or her professional endeavor to the equine species, whether it be practice in the field, in research, in regulatory medicine, in veterinary education or other professional pursuits.

In human medicine, gene therapy, genetic mapping, imaging systems and therapeutic technologies are promising a quality of life not imagined in the recent past. The equine practitioner, too, is part of these developments. Veterinary researchers in the laboratory and equine practitioners in the field are continuously evaluating, developing, refining and perfecting methods to improve the quality of life for their equine patients. The result is that veterinarians are saving horses today whose injuries and diseases would have been life-threatening a decade ago.

A veterinarians' formal education does not end with the awarding of a D.V.M. (Doctor of Veterinary Medicine) or V.M.D. (Veterinary Medical Doctor) degree. To keep abreast of current medical technology and advances, veterinarians, like human physicians, are required to continue their education. Equine practitioners must earn a minimum number of hours of continuing education credit per year. This number is regulated by each state.

Although all equine veterinarians have a foundation in general veterinary medicine, some specialize in certain areas such as surgery, ophthalmology, reproduction or internal medicine, to name just a few. Certain organizations require approval from the professional board to certify a specialist's or practitioner's expertise.

Diagnosis and treatment of equine problems require skills beyond knowledge of anatomy, physiology, chemistry and pharmacology. Equine veterinarians must be savvy fact finders, asking horse owners the right questions to extract the necessary information to assist in diagnosis. They must be able to communicate technical information in laymen's language. Furthermore, keen insight and sensitivity are absolute necessities in treating patients that weigh many times more than the average person.

Handling a 1,000-pound animal in discomfort or pain is only one challenge faced by equine veterinarians. Unlike most small animal veterinarians, the majority of equine practitioners have a rather nomadic way of life, travelling from farm to farm, horse show to horse show, or racetrack to racetrack.

Like other health care providers, equine veterinarians face ethical and professional dilemmas. Simple black-and-white solutions don't always exist, and veterinarians sometimes disagree among themselves about the best treatment. A veterinarian takes an oath that he/she must comply with throughout his/her career. The American Association of Equine Practitioners enforces ethical behavior of its members, denying association membership to any practitioner found guilty of unethical behavior.

Many equine practitioners go beyond treating individual horses to providing leadership in many aspects of the horse industry. Equine veterinarians are becoming increasingly involved in helping to solve problems and plan for the future in such areas as ethics and welfare, racing, three-day eventing and competitive events. Many veterinarians are generous with their time and avail themselves to civic groups, youth groups, national organizations, national breed associations and the United States Department of Agriculture. And -- unlike most of their human counterparts -- the equine veterinarian still makes "barn" calls.

ON CALL: "On Call" is a media-awareness program initiated by AAEP in 1991 with the support of television networks and racetracks to provide accurate veterinary medical information and follow-up in the event of an equine injury during a live-broadcast race. The vehicle for this information is the veterinarian representing AAEP's On Call team, who acts as a conduit between the on-track veterinarian or practitioner attending to the injured horse and the reporter relaying events to the audience, either broadcast or print.

On Call spokespersons are available to the media at live-broadcast races that allow enough time for a follow-up report in the case of an injury. These include the Triple Crown races (Kentucky Derby, Preakness Stakes, Belmont Stakes) and the Breeders' Cup. Since 1991, On Call veterinarians have assisted the media at every racing broadcast on ABC, NBC, CBS and ESPN. These include Thoroughbred, Quarter Horse and Standardbred races.

Most recently, the On Call program has been expanded to include other televised equine events, as well as equine events with a large spectator base, including the Olympics and the American Quarter Horse Association's World Championship show.

PRE-RACE EXAMINATIONS

A pre-race inspection of all horses scheduled to race should be performed by regulatory (commission or association) veterinarians sufficient to determine, in the veterinarians' professional opinion, whether such horses are able to compete. AAEP recognizes that pre-race inspection is only one of many components involved in monitoring the health and welfare of the equine athlete. AAEP further recognizes that the most thorough pre-race inspection cannot prevent all racing injuries nor can it detect all pre-existing conditions. The primary responsibility for the condition of the horses that are entered to race rests with the trainer.

Ideally, a suggested pre-race inspection should include: proper identification of each horse; pre-race observation of each horse in motion; manual palpation when indicated; close observation in the paddock and saddling area during the parade to post, at the starting gate and during and after the race; and any other inspection deemed necessary. An ongoing confidential record of inspection of individual horses should be maintained for use in subsequent evaluations.

Following inspection, regulatory veterinarians should recommend to the stewards or judges the scratching of any horse that, in their opinion, is physically unfit to race. Regulatory veterinarians should also have authority to determine when a horse is physically able to return to competition. A list of horses not suitable for racing should be maintained and criteria established regarding how a horse is added or removed from that list. Owners and trainers should be advised that their horses have been added to that list. The names of horses on veterinary lists and the reasons for their disqualification may be distributed among neighboring racing associations within a state or group of states in the same geographic area. It is the responsibility of the racing association or commission to employ and adequately compensate a sufficient number of veterinarians and support staff to thoroughly and effectively accomplish these tasks.

CHARTS & ANATOMY

GLOSSARY OF RACING LANGUAGE

PRACTICING VETERINARIAN'S DUTIES AND RESPONSIBILITIES

The duties of the practicing veterinarian primarily revolve around sustaining health, preventing and testing for equine diseases, and maintenance of the animal's physical condition and racing soundness. The procedures and services that the practicing veterinarian performs for his/her clients are varied and numerous.

The practicing veterinarian is expected to be thoroughly familiar with all rules relating to veterinary practice at each racetrack by direct contact with the commission and association veterinarian, and by procuring and understanding applicable rules.

Practicing veterinarians are expected to assist the commission or association with matters that are considered pertinent to the smooth functioning of the racing process.

Veterinarians who practice at the racetrack are expected to have input with other practicing, commission and association veterinarians when problems involving the well-being of the horses at the racetrack arise.

Veterinarians who practice at the racetrack are expected to maintain medical records consistent with the professional practice of veterinary medicine, the rules and regulations of the local racing jurisdiction and the requirements of the State Practice Act.