Challenge of Assessment

This type of horse presents the veterinarian with a diagnostic challenge that may involve assessment not only of the horse, but also of the horse and rider together and the rider’s ability. Such an assessment requires knowledge of the sport in question and an ability to recognize when the problem is a lack of athletic ability or a mental problem rather than a pain-related musculoskeletal disorder or some other pathological condition, such as an upper airway disorder. The assessment also requires good knowledge and appreciation of how horses normally move and the variations among different breeds and types and an ability to recognize subtle changes in gait, such as a slightly reduced lift to the stride or stiffness in movement of the back. The assessment requires basic knowledge of equine locomotion and how gait may be modified by pain and also requires the ability to recognize when a rider may actually be creating the problem. Training methods and style of riding may contribute to the development of lameness.

This section sets out to discuss some of the different problems that may be encountered and the types of conditions that may be the cause of poor performance and to suggest some methods of approach to diagnosis. These may vary to some extent depending on whether the clinician is dealing with a competent professional rider or trainer or an inexperienced or even experienced amateur who lacks ability.

History

It is essential to obtain a comprehensive history to determine whether the horse has genuinely performed better previously at this level of competition, or moved better, and precisely what changes have been observed. It is important to listen carefully to the owner to properly understand the perceived problem, however small it might be. This is particularly important if the clinician does not have prior knowledge of the horse.

Determine the answer to the following questions:

Viewing videos of the horse when it was performing normally sometimes can be helpful to compare with the findings of your own clinical evaluation. If the horse has recently changed ownership, comparing video recordings of the horse ridden by the previous rider and by the current rider can be useful to determine whether a change in riding style or training techniques may be responsible for making a previously subclinical problem become symptomatic, or to determine if the problem could be related directly to the manner in which the horse is being worked.

The types of clinical problems that may be encountered are listed in Box 97-1.

BOX 97-1 Types of Clinical Problems

• Not jumping as well: knocking down rails. This may be pain related or may be caused by the rider presenting the horse poorly to the fence.

• Not jumping as well: stopping. This may be a horse or rider confidence or ability problem, or may be pain related.

• Not making distances in combination fences. This may occur because the horse is landing too steeply, saving one or both front feet and therefore having too much ground to make up, or through lack of push from behind, reflecting a hindlimb lameness. Alternatively, if the horse is presented poorly to the first element of the fence, the subsequent elements become increasingly difficult.

• Reluctance to land leading on a specific leg. This can reflect a forelimb or less commonly a hindlimb lameness. Peak ground reaction forces at landing are significantly greater in the trailing forelimb than in the leading forelimb¹; therefore a tendency to land with the right forelimb leading is most likely a reflection of right forelimb pain. However, stress on the suspensory apparatus is greater in the leading forelimb; therefore in association with suspensory pathology a horse may avoid landing with the affected limb leading.

• Napping (resistance) on the approach to a fence off a turn. Nappiness may be pain related or behavioral.

• Not jumping straight (e.g., jumping to the right), with a tendency for the hindlimbs to drift toward the direction in which the horse is jumping (to the right). This usually reflects pain or weakness in the ipsilateral hindlimb of the side to which the horse is jumping. Less commonly the problem may be caused by reluctance to land on the contralateral forelimb (e.g., the left).

• Loss of hindlimb power. This may be caused by back pain or hindlimb lameness. Less commonly it may be the result of low-grade hindlimb ataxia.

• Change in the shape the horse makes over a fence—for example, loss of bascule (jumping with a rounded arc over a fence). This may reflect back pain or forelimb or hindlimb lameness, or possibly gastric ulceration. It may also reflect the way in which the horse is presented to the fence.

• Rushing fences. This can be the way an excitable horse always jumps, but if the horse used to jump normally, rushing the fence usually reflects a painful problem. However, if the horse has been stopping for whatever reason and has been chased to the fences, it will inevitably rush. If a horse is overly restricted by the rider’s hands it may also try to rush to escape.

• Loss of action. This can reflect the way in which the horse has been ridden and trained. Some loose, free-moving young dressage horses become much more restricted in their stride when ridden exercise is commenced. An apprehensive rider may restrict a potentially exuberant horse. A bored horse, particularly with a Warmblood mentality, may just switch off and refuse to go forward freely and loosely. Loss of action also may reflect forelimb or hindlimb lameness or back pain.

• Stiffness. Stiffness should be evaluated carefully to differentiate loss of action and back stiffness from restriction of gait caused by a bilateral forelimb or hindlimb lameness.

• Inability to perform medium or extended trot. Unless a horse is properly balanced with adequate hindlimb impulsion, it cannot perform medium or extended trot. Horses vary considerably in the ability to collect and extend. In general the Thoroughbred breed has much less natural ability than many of the Warmblood breeds. Some horses have to learn how to perform a medium and an extended trot and must first develop sufficient muscular coordination and power before they are able to do so. However, if a horse was previously able to work in medium and extended paces and now cannot do so, or if the rhythm becomes irregular, this can reflect forelimb or hindlimb lameness or back pain.

• Inadequate hindlimb impulsion in trot, with a tendency to break to canter if asked to work harder. This usually reflects hindlimb lameness.

• Difficulty in performing specific dressage movements—for example, right half pass. This often reflects a back or sacroiliac joint region problem or hindlimb lameness.

• Tendency to become disunited behind in canter. This usually reflects hindlimb lameness. However, it is important to recognize that young horses can find maintaining true canter difficult, sometimes just in one direction, or sometimes in both directions. This often can be overcome by training and development of muscular strength and coordination. Some trained horses that canter true when ridden may become disunited when cantering on the lunge. Hindlimb lameness may predispose to a horse becoming disunited. If the problem occurs to a similar extent on both reins, it often reflects a bilateral problem, but if it occurs on only one rein, the problem is more likely to be unilateral.

Although the canter stride is initiated by the trailing hindlimb, which bears weight alone, the stance time, peak vertical ground reaction forces, and range of motion of the proximal limb joints are higher in the leading hindlimb.^2,3 Therefore if the horse consistently becomes disunited on the left rein, this is likely to reflect discomfort in the leading left hindlimb.

• Late flying changes, or difficulty in changing from right to left or from left to right. This usually results from hindlimb lameness.

• Inability to maintain a consistent rhythm in piaffe, passage, or canter pirouettes. This usually reflects a hindlimb lameness.

• Unlevelness in certain movements. Mild irregularities in rhythm may be detectable only in certain movements—for example, left half pass and right shoulder in. Such irregularities can reflect forelimb or hindlimb lameness or may be induced by the rider overrestricting with the hand and not creating sufficient hindlimb impulsion. Dressage riders often refer to bridle lameness, implying that lameness is not true because it cannot be detected when the horse is trotted in hand or lunged. This usually is a misnomer, because most bridle- or rein-lame horses have a genuine lameness, which may be apparent only when the horse is ridden.

• Crookedness, or reluctance to take the bit evenly on the rider’s left and right hands. This can result from a training problem or can be caused by lameness or unwillingness to accept the bit because of oral pain. Less commonly it may reflect temporomandibular joint pain.

• Taking unequal-length strides behind in walk, despite appearing sound in all other gaits. This can be seen in some otherwise normal horses that show no response to systemic administration of analgesic drugs. This syndrome is generally seen only when the horse is ridden and in some horses is apparent only when the horse walks on the bit, and not when it walks on a long rein. It is characterized by a shortened cranial phase of the stride. Local analgesic techniques from the foot to the coxofemoral joint usually have no effect on this gait. Radiographic, ultrasonographic, and nuclear scintigraphic examinations are usually unrewarding. Alternatively, irregular strides may reflect hindlimb lameness also seen at other gaits.

• Lameness apparent only when the horse is working to a contact, on the bit, and not when worked on a long rein. Problems in these horses can be difficult to solve. Some reflect a forelimb lameness, upper forelimb muscular pain, or caudal cervical pain.

• Inability to engage the hindlimbs on the forehand. This usually reflects hindlimb lameness or back pain.

• Hanging, or on one line. This often reflects hindlimb lameness or forelimb lameness in a Standardbred.

• Loss of power cross-country. This may be caused by subclinical exertional rhabdomyolysis, discomfort associated with superficial digital flexor tendonitis, or other causes of lameness. Alternatively, the horse may have acute-onset back muscle pain.

• Reluctance to jump drop fences. This can be a rider or horse confidence problem, but it also may be caused by forelimb lameness or back pain.

• Cold-backed behavior when tacked up or first mounted. This is manifest by the horse tensing, roaching the back, sometimes freezing and refusing to walk forward, and then sometimes exploding into a series of violent bucks. Often this abnormal behavior stops within a few minutes, and the horse then works completely normally.

Cold-backed behavior can be unrelated to pain and may be a problem initiated by pain, which then becomes a behavioral response. Such behavior may reflect fear, especially if a rider has fallen off several times, and less commonly is associated with chronic pain because of a rib fracture, fractured sternum, or nerve-related pain.

The behavior may be precipitated by rapidly tightening the girth, especially if the girth has an elastic inset.

Cold-backed behavior is generally manageable by an experienced rider, but such behavior is potentially dangerous to a nervous or inexperienced rider. Affected horses should be tacked up slowly and the girth tightened progressively, walking the horse forward each time. The horse should be lunged and made to go forward at the trot and the canter before being mounted. The rider should be legged up onto the horse and should not attempt to mount from the ground.

Horses with cold-backed behavior may improve with careful management but should never be trusted completely.

• Bucking. Bucking behavior can be similar to cold-backed behavior, or it may occur only after the horse has been ridden for a period. Although the horse may appear to buck with a flexible back, primary back pain is sometimes the underlying cause. Back pain secondary to hindlimb lameness may also result in bucking. Bucking can be a behavioral problem unrelated to pain.

• Bucking and kicking out to one side is often a manifestation of sacroiliac joint region pain.

• Rearing. Rearing is often part of nappy or resistant behavior: the horse tests the rider. Relatively rarely is rearing associated with a pain-related problem such as sacroiliac region pain.

• Bolting. Bolting may result from pain of any cause (e.g., bilateral hindlimb proximal suspensory desmitis) or may be a behavioral problem.

• Tendency for the saddle to slip to one side. This may be because of the rider’s inability to sit straight, a poorly fitting saddle, or unilateral hindlimb lameness. The saddle usually slips to the side of the lame hindlimb.

• Reluctance to work on the bit. Difficulties in working on the bit may be one of the first signs noted by a rider when the horse develops a minor musculoskeletal problem involving the back or limbs, or a mouth problem.

• Head-shaking behavior when ridden. There is a poorly understood syndrome in which horses head-shake generally only when ridden, although if the horse is severely affected the behavior may also be apparent on the lunge and occasionally in the stable. Such horses are usually worse in the summer months. Affected horses sneeze frequently and may strike out with a forelimb or repeatedly try to rub their nose on one or both forelimbs. The behavior may be controlled in some horses by placement of a net over the horse’s nostrils. Mildly affected horses may perform normally when jumping and may show signs only when worked on the flat. Severely affected horses may be virtually impossible to ride.

• Unwillingness to work. This may be behavioral or pain related. Warmblood breeds in particular are strong-willed horses that easily recognize when their rider is not competent enough, and rapidly a vicious circle can ensue. However, reluctance to work equally may reflect lameness or back pain.

• Nappy (resistant) or evasive behavior. This may reflect pain or the dominance of the horse over the rider. Although some horses have a compliant temperament and never take advantage of an incompetent handler or rider, other horses rapidly recognize lack of ability, or apprehension of the rider, and develop resistant or awkward behavior.

• Progressive agitation with work, with or without loss of action. This may reflect the horse’s temperament or pain caused by exertional rhabdomyolysis, for example.

• Episodic complete loss of rhythm and lack of synchronization of movement of all limbs. This may reflect a multilimb lameness, but it may also be an evasion or reflect tension. If the horse puts its head up and hollows its back, maintaining a regular rhythm is difficult. Working the horse in draw reins, changing the work environment, and using sedatives or analgesic drugs can help to differentiate a pain-related problem from an evasion.

Investigation of this type of horse is time-consuming and usually requires repeated clinical examinations, together with ancillary diagnostic techniques. Ideally the horse should be in full work at the time of the investigation. The horse must be assessed in its entirety, including full visual appraisal and palpation at rest, evaluation of the horse moving in hand and on the lunge on soft and hard surfaces, and assessment of the response to flexion tests. Ridden exercise is crucial.

Clinical Assessment

It is generally essential to see the horse ridden by the regular rider, performing the movements that are causing difficulty. If the veterinarian does not feel competent to judge the rider and the influence the rider may be having on the problem, the assistance of a professional rider or trainer may be necessary. However, it is important to recognize that not all so-called “experts” are truly experts, and the advice of a misguided professional may serve only to muddy the waters.

It is important to appreciate the profound influence that back pain arising from the thoracolumbar or sacroiliac regions can have over the horse’s entire manner of moving. Back pain not only may induce back stiffness, but also may result in the horse holding itself tensely and not accepting the bit properly, with a restriction in stride length and reduced lift to the stride in all limbs. Bilateral hindlimb proximal suspensory desmitis may have a similar effect.

Clinical assessment of back pain is not easy. A normal horse should be able to flex and extend the thoracolumbar spine repeatedly in the sagittal plane and flex from side to side with ease, without inducing tension in the epaxial muscles. Holding the back stiffly, sinking on the hindquarters to avoid extension, and showing evidence of muscle fasciculation or spasm may indicate pain. Alteration of facial expression and a tendency to bite or kick out may also reflect pain. However, some nervous, thin-skinned horses guard the back and do not flex normally unless they are relaxed completely. Some stoical cob-type horses show little response at all. Some horses respond to digital palpation, whereas in others firmer pressure must be applied, using, for example, the closed tips of a pair of artery forceps to induce flexion and extension of the back.

In a normal horse at the trot and canter appreciable up-and-down movement of the back occurs, along with swing from side to side, with an easy swinging movement of the tail. The degree of movement is to some extent determined by the horse’s natural athleticism. The degree of movement often is reduced with back pain. The degree of restriction of movement reflects the temperament of the horse and hence its reaction to pain and the severity of the pain. Clinical signs of back pain may be subtle unless the horse is assessed while it is ridden. Restricted back mobility may be more obvious when the rider sits continuously in the saddle, in sitting trot and canter, compared with when the rider sits lightly, or rises up and down in the trot. Movement of the tail may be restricted. The restricted movement of the back may be much more obvious to a rider than to an observer and may induce back pain in the rider. Further investigation of thoracolumbar and sacroiliac pain is discussed elsewhere (see Chapters 50 through 52).

It is important to recognize that many horses with hindlimb lameness show signs only when the horse is ridden. The modification of stride variables because of hindlimb lameness is much less than for forelimb lameness. The diagonal on which the rider sits in rising trot often substantially influences the lameness. Lameness is usually most obvious when the rider sits on the diagonal of the lame limb and may be unapparent on the other diagonal. The horse may deliberately try to make the rider sit on the nonlame diagonal. Low-grade irregularities in gait may be most apparent when the horse changes direction when performing small figures of eight (e.g., loss of rhythm, swinging the hindquarters to the outside of the circle, crossing the inside hindlimb in underneath the body during protraction, coming slightly above the bit) or when decelerating from canter to trot or from trot to walk (e.g., failure to “sit down” behind and engage the hindlimbs), or may be manifest as hopping into trot from walk. Subtle delayed release of the patella may be apparent only as a horse decelerates.

Recurrent low-grade equine rhabdomyolysis may occur almost every time an affected horse is ridden, without any of the classical clinical signs of tying up. Measurement of serum concentrations of creatine kinase and aspartate transaminase reveals elevation of both. Some of these horses have increased radiopharmaceutical uptake in the affected muscles in bone phase images if examined using nuclear scintigraphy.

It is often necessary to compare the horse’s performance when ridden by a different rider, bearing in mind that riders with varying abilities can make horses appear different, and riders of differing weights and ability to follow the rhythm can make a great difference in the horse’s gait. A good rider can make a slightly nappy horse go forward freely, with a totally rhythmical stride, whereas a less competent rider may be unable to ride the horse through, and the horse may take uneven steps behind because it is not going forward enough. A heavy rider or a rider who is unable to ride properly in balance may induce hindlimb lameness. The same horse ridden by a lighter rider may be completely sound. A horse that evades the bit and runs along with its head in the air may take irregular steps in front and behind and appear stiff in the back, especially if a rider attempts to make the horse work on the bit. The same horse, when encouraged to submit and work on the bit when ridden by an expert with draw reins, may appear completely different, relaxing the back, stepping under more from behind and becoming much more rhythmical. It is often necessary to separate the owner from the horse diplomatically to assess how the horse responds to a skilled rider over several days.

It is also important to recognize that inappropriate work patterns on the flat or over fences actually can induce musculoskeletal pain, which may progress to chronic lameness. For example, repeatedly placing the horse too close to a jump (putting the horse in deep), which also alters the bascule over the fence and the way in which the horse lands, may predispose the horse to patellar ligament soreness. This may alter the horse’s way of moving and predispose to the development of pain elsewhere. In the early stages the problems potentially may be managed with a change in work program and methods of training the horse. However, long-term problems may be more difficult to resolve satisfactorily.

Paradoxically, it may be helpful to see a usually well-ridden horse with a subtle performance problem ridden by a less clever rider. The professional rider may be making subtle adjustments to the gait inadvertently and thereby masking gait irregularities reflecting low-grade lameness.

The fit of the tack and its suitability must be evaluated. The veterinarian should not assume that because the saddle was fitted by a professional saddle fitter that it necessarily does fit. The position of the bit in the mouth, the size of the bit relative to the size and shape of the mouth, and the suitability and the severity of the bit should all be assessed. The mouth should be inspected carefully to ensure that no lacerations of the tongue, gums, or corners of the horse’s mouth have occurred and that the teeth have no sharp points or hooks.

In some instances the horse may appear to be clinically normal, and it is necessary to try to establish whether the complaint is indeed pain related. In my experience, phenylbutazone is the most effective analgesic drug for trying to determine whether a problem is pain related. The drug must be given at a high enough dose (minimum 4.4 mg/kg twice daily) for long enough (at least 7 days if the horse does not respond within 2 to 3 days). A comparison with records of the horse’s attitude, behavior, and action before, during, and after treatment should be assessed as objectively as possible. A positive response confirms the presence of a pain-related problem, whereas a negative response does not definitively exclude a pain-induced problem. The potential exists to create a placebo effect for the rider, and in selected horses, “blinding” the rider to the treatment may be worthwhile.

If the problem seems to induce considerable anxiety and tension when the horse is worked, mild tranquilization with acepromazine or sedation with detomidine can be helpful to determine if the problem is pain induced or reflects tension. The tension actually may be induced by the rider or the environment in which the horse is worked. Working the horse in a different situation with another skilled rider can be helpful.

If the horse is fresh and exuberant, minor gait abnormalities can be difficult to assess, especially in a big moving dressage horse. In these circumstances mild sedation can be useful.

It is important to try to determine if a problem reflects pain or weakness caused by a neurological problem. Low-grade hindlimb toe drag may reflect a mild proprioceptive deficit rather than lameness. When in doubt, a comprehensive neurological examination should be performed (see Chapter 11). This is particularly important in areas (North and South America) where equine protozoal myelitis occurs. In other countries it is important to establish whether the horse has ever been to America.

It is also important to recognize that some horses that are mild wobblers, with mild hindlimb gait abnormalities seen when moving loose or in hand, may actually move loosely and freely when ridden, with apparently good coordination, and perform rather well in low-level dressage and other competitive disciplines despite a problem. However, such horses usually lack strength and coordination to perform more advanced dressage.

Common Performance Problems

The most common causes of poor performance not related to readily recognizable overt lameness are listed in Box 97-2.

These horses are time-consuming to investigate, often requiring a multifaceted approach to diagnosis. It is important to recognize that the failure to perform optimally may be the result of several problems, and recognition of all of these may be crucial to successful management. Determination of all the postulated sites of pain causing poor performance is based on an assessment of a detailed history of performance; the results of palpation including the response to stimulation of acupuncture points; evaluation of the horse moving in hand, on the lunge, and ridden, both when work is first initiated and later in the work program; and the response to flexion tests and chiropractic assessment of joint mobility, sometimes combined with assessment of the response to local analgesic techniques. Although it is often essential to see the regular rider riding the horse, separating the horse from the rider for several days can be helpful, particularly with horses ridden by amateurs or semiprofessionals. It is essential to have access to adequate facilities to see the horse ridden (or driven) properly on a daily basis and to be able to perform local analgesic techniques and then reevaluate the horse ridden or driven under the same circumstances.