The musculoskeletal system in horses encompasses the bones, muscles, tendons, ligaments, and joints that facilitate movement and provide structural support. This system is essential for locomotion, athletic performance, and overall health in equine species. The equine skeleton consists of approximately 205 bones, which are connected by joints and supported by a network of muscles and connective tissues. Tendons connect muscles to bones, while ligaments link bones to other bones, contributing to joint stability. The musculoskeletal system is subject to various conditions, including injuries, degenerative diseases, and developmental disorders, which can impact a horse's mobility and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, pathology, and treatment of musculoskeletal conditions in horses.
Ostblom L, Lund C, Melsen F.A histological investigation of navicular bones from 8 horses with navicular disease was carried out to investigate the aetiology of the radiological findings. Two of the horses were double labelled with tetracycline before slaughter in order to assess the vitality of the diseased navicular bone. The examinations revealed no evidence of loss of vitality in the diseased bone areas or in surrounding tissues. A very high rate of remodelling indicated by resorption and formation of bone was present in all cases. This was shown microscopically by the high number of osteoclasts and osteoblasts prese...
Snow DH, Munro CD, Nimmo MA.The effects of 7 weekly injections of the anabolic steroid nandrolone phenylpropionate (400 mg) were investigated in 4 healthy, mature geldings. Measurement of body weight, nitrogen retention and plasma urea failed to demonstrate a consistent anabolic effects. Examination of biopsies from the semitendinosus and biceps femoris muscles showed no alteration in water content or glycogen concentration with treatment. Similarly no changes were found in the activities of 6 muscle enzymes. However, a significant increase in the proportion of fast twitch low oxidative fibres of the biceps femoris was o...
Nimmo MA, Snow DH, Munro CD.The effect of 11 weekly injections of nandrolone phenylpropionate (400 mg) on some skeletal muscle parameters was investigated in 6 Thoroughbred geldings undergoing training. Three muscles were sampled, the middle gluteal, the biceps femoris and the semitendinosus. Training alone produced increases in the percentage of fast twitch high oxidative fibres (FTH), glycogen content and the activities of citrate synthase, 3-hydroxyacl CoA dehydrogenase and cytochrome oxidase. In contrast the training programme did not alter water content, total protein content, the activities of lactate dehydrogenase...
Biewener AA.Measurements of the cross-sectional geometry and length of bones from animals of different sizes suggest that peak locomotory stresses might be as much as nine times greater in the limb bones of a 300 kg horse than those of a 0.10 kg chipmunk. To determine if the bones of larger animals are stronger than those of small animals, the bending strength of whole bone specimens from the limbs of small mammals and bipedal birds was measured and compared with published data for large mammalian cortical bone (horses and bovids). No significant difference (P greater than 0.2) was found in the failure st...
Trotter GW, McIlwraith CW, Norrdin RW, Turner AS.Degenerative joint disease of the proximal interphalangeal joint was diagnosed in 9 joint of 6 horses. All of the horses were 3 years old or younger and the affected joints were in the hindlimbs. Radiographic evidence of osteochondrosis involving the distal end of the proximal phalanx was apparent in 5 joints. Lameness and local soft tissue swelling were prominent in all cases. In 1 horse euthanatized tissues because of lameness, histologic examination of joint tissues revealed osteochondrosis as well as severe osteoarthritis. Surgical arthrodesis of the affected joint was performed on 2 horse...
Bramlage LR, Hanes GE.A 3-year-old Thoroughbred mare was examined because of hindlimb lameness from incomplete fracture of the tibia, which became a complete diaphyseal fracture during the examination. The fracture was repaired by open reduction and internal fixation with lag screws and 2 neutralization plates. A cranial approach was used and the plates were placed craniolateral and medial on the tibia. At 18 months after surgery, there was no evidence of complications resulting from the fracture or its repair. It was concluded that a cranial approach with craniolateral and medial plate placement allows easier inse...
Edwards GB.During a 3 year period 20 horses with bone spavin were treated by surgical arthrodesis of the affected joints. The horses chosen for surgery were those with osteoarthritis, but with little or no evidence of periostitis. Whenever possible they were examined periodically during the postoperative period to evaluate the lameness and to assess the progress of ankylosis by radiography. Three of the horses were still lame 12 months later. The remainder returned to normal work, although one subsequently developed spavin in the other hock and was destroyed. The earliest return to soundness was 3 1/2 mo...
Quinlan TJ, Goulden BE, Barnes GR, Anderson LJ, Cahill JI.The nerve supply to the intrinsic laryngeal muscles of the horse was studied by gross dissection and by electromyography which was carried out before, during and after section of various intralaryngeal nerve branches. The anatomical relationships and passage of the laryngeal nerves throughout the larynx were defined. Unlike the dog and man there was no evidence of the passage of motor nerve fibres from one side of the larynx to the other.
Jeffcott LB, Dalin G, Drevemo S, Fredricson I, Björne K, Bergquist A.Back pain was induced in Standardbred horses by multiple intramuscular injections of a concentrated lactic acid solution into the left longissimus dorsi muscle. The investigation was divided into 2 parts. In Stage 1, 2 trotters were exercised on a treadmill and filmed by high speed cinematography before and after the induction of back pain. No signs of hindlimb lameness were evident and no quantitative changes in the components of the gait resulted, but a noticeable reduction was seen in performance capacity. Stage 2 involved a more intensive clinical and cinematic analysis of 3 horses. In the...
Nimmo MA, Snow DH.To ascertain the effects of sprint and endurance exercise on the time course of skeletal muscle mitochondrial changes, an ultrastructural study was conducted on four Thoroughbred horses. Skeletal muscle biopsies were taken at various intervals during and after the exercise. Transient mitochondrial alterations of varying degrees were observed following both types of exercise and were considered to be related to the development of fatigue. The degree of distortion of mitochondrial structure is considered not to represent the in vivo condition but the state of responsiveness to the fixation mediu...
Fedak MA, Heglund NC, Taylor CR.This is the second paper in a series examining the link between energetics and mechanics of terrestrial locomotion. In this paper, the changes in the kinetic energy of the limbs and body relative to the centre of mass of an animal (EKE, tot) are measured as functions of speed and body size. High-speed films (light or X-ray) of four species of quadrupeds and four species of bipeds running on a treadmill were analysed to determine EKE, tot. A mass-specific power term, EKE, tot/Mb was calculated by adding all of the increments in EKE during an integral number of strides and dividing by the time i...
Steiss JE, Yuill GT, White NA, Bowen JM.A force plate system for measurement of the vertical component of the force applied by a horse's limb on ground contact was modified. The modifications included use of steel supporting posts for improved durability and an additional strain gauge on each arm of the Wheatstone bridge for increased sensitivity and temperature compensation. Data from clinically normal horses are provided to indicate the performance obtained with these modifications of the force plate system.
Stick JA, Jann HW, Scott EA, Robinson NE.We reviewed 91 cases of laminitis in horses admitted to the Michigan State University Veterinary Clinical Center between Jan 1, 1973 and Dec. 30, 1978. From information in the case records and from the results of a telephone questionnaire, cases were classified into 4 categories on the basis of return to athletic function. The degree of pedal bone rotation was inversely correlated with return to athletic performance. Horses with less than 5.5 degrees rotation returned to former athletic function, whereas horses with more than 11.5 degrees rotation lost their use as performance animals. Ponies ...
Stewart B, Reid CF.Osseous cyst-like lesions of the medial femoral condyle were found in 32 horses admitted to the University of Pennsylvania between 1971 and 1978. Sex or breed predilection was not found. In 12 horses, osseous cysts were found in both hindlimbs. Of the 25 horses on which follow-up information was obtained, 16 became sound and useful between 4 months and 1 year after diagnosis. Horses that became lame before 3 years of age had a better chance for later soundness. Horses that became sound had significantly smaller cysts than those that remained lame.
Riemersa DJ, Schamhardt HC.A clamp designed for holding tendons in force/elongation studies is described. No slippage occurred when tensile forces up to 13,800 N were applied to horses digital flexor tendons fixed in this clamp.
Adams SB, Fessler JF, Thacker HL.FIBROMAS arise from connective tissue and occur in all domestic animals (Smith, Jones and Hunt 1972; Stannard and Pulley 1978). They are most frequently noted in the dermis or subcutis, but may be present wherever connective tissue occurs. In the dermis and subcutis of the horse fibromas are grossly similar to sarcoids and may be difficult to differentiate (Baker and Leyland 1975). Fibromas have been described as tumours of the tendon sheath or tendon proper in man (Flynn 1975), but have not been described in this location in the horse.
Jakovljevic S, Gibbs C, Yeats JJ.The clinical features, radiographic findings, management and outcome in 13 cases of traumatic fracture of the hock joint are reported. The principal fracture sites were the distal tibial malleoli (5 cases), the fibular tarsal bone (4 cases), the tibial tarsal bone (3 cases) and the proximal end of metatarsal IV (one case). An additional small chip fracture of the central tarsal was noted in 2 cases. Three horses were destroyed immediately after diagnosis, 2 failed to recover following surgical intervention and one remained lame and was destroyed after 3 months' rest. Seven horses recovered com...
Dzongowska-Dzongu T, Kotoński B, Hutny J.Alpha-1,4 leads to 1,4-glucosyltransferase preparations from horse muscles and serum were studied. The enzyme proteins from both tissues are very similar. Both proteins have a molecular weight of 240 000 and consist of four subunits of 60 000 daltons each. pH 5,0 is optimal for the activity. Only substrates with alpha-1, 4-linkages can serve as glucosyl donors for transferase reactions. Km values for both enzymes differ very slightly. At low substrate concentrations the hydrolytic activity can be found in addition to transferase reactions. At the concentration of the substrate higher than 40 m...
Attenburrow DP.Techniques developed for the detection and simultaneous recording of certain events in the respiratory and limb cycles are presented. The respiratory cycle and limb cycle were found to be in-phase only at the canter and gallop. The significance of any time relationship between events in respiration and in locomotion is discussed.
Kelmer G, Kramer J.Shortening of the deep digital flexor tendon was performed by tenotomy, overlapping and anastomosis. The procedure was performed on a two-year-old Quarter Horse Mare with distal interphalangeal joint hyperextension with subluxation and metatarsophalangeal joint hyperextension. These problems originated from damage to the digital flexor tendons, presumably due to previous distal limb trauma. The procedure markedly improved the mare's level of comfort, degree of ambulation and limb conformation. Two years following surgery the mare was comfortable at pasture.
Deane NJ, Davies AS.A photographic study of the angles of 71 carpal joints of horses at the end of a race has shown that overextension of the joint is normal at this stage. Further study is needed to determine the factors which may influence hyperextension, and whether they are relevant to carpal injury.
Pérez W, Martin E.Thirteen fresh equine heads were dissected in an attempt to determine the cause of a groove frequently found on the dorsal border and medial side of the nasal process of the incisive bone. This groove appeared on both sides in 40 out of 44 equine skulls. The sulcus seems to be caused by the combined action of the lateralis nasi muscle and the medial accessory cartilage of the nose (cartilago nasalis accessoria medialis). Other sulci found on the nasal process of the bone may be explained as impressions caused by nerves.
Marks D.The most common causes of back pain and their medical treatment are discussed. These include: dermatologic problems and conditions resulting from saddle trauma; discomfort and stiffness owing to injured paraspinal muscles; pain associated with supraspinous ligament damage; osseous pain and nerve dysfunction related to the spine and sacroiliac area; and neurologic diseases that can manifest as back pain. Bitting problems, cervical pain, and coexisting lameness are also considered.
Palmero J, Hollingsworth S, Kass P, Moore S, Pusterla N.N-butylscopolammonium bromide (NBB), an anticholinergic muscarinic antagonist, was assessed as a mydriatic agent for field examination of equine eyes. Six adult horses were randomly assigned to four treatments with 2 weeks washout between treatments: (1) topical saline/IV saline (negative control); (2) topical tropicamide/IV saline (positive control); (3) topical NBB/IV saline; or (4) topical saline/IV NBB. Horizontal and vertical pupil diameters, temperature, pulse, respiration, pupillary light reflexes (PLRs) and mydriasis sufficient to perform complete fundic examination were recorded. Trop...
Smith MR, Wright IM.A minimally invasive arthroscopic technique for removal of fractures of the lateral malleolus of the tibia is considered to be beneficial but data to this effect are required. Objective: Arthroscopic removal of fractures of the lateral malleolus of the tibia is technically feasible, provides a comprehensive evaluation of the tarsocrural joint and enables removal of remote comminuted fragments and disrupted short collateral ligaments. The technique is associated with low patient morbidity, requires only short periods of hospitalisation and affords a good prognosis to affected horses. Methods: T...
McDonell WN, Pascoe PJ, Lindsay WA, Burgess ML.The use of the wick catheter to measure intracompartmental muscle pressure in equine muscle was documented. The presence of muscle compartments involving the extensor carpi radialis muscle and the long head of the triceps brachii was demonstrated by anatomic dissection and radiographic technique. The wick catheter was capable of accurately measuring pressures within both of these compartments. Furthermore, the wick catheter was sensitive to pressure changes resulting from external compression of muscle compartments. Manipulation of systemic blood pressure and PaCO2 in 1 anesthetized horse did ...
Stieger-Vanegas SM, Kippenes-Skogmo H, Nilsson E.An enostosis-like lesion was diagnosed in the left femur of a Swedish Warmblood horse that had a left hindlimb lameness of 3 weeks duration. With scintigraphy using technetium 99m-hydroxymethylene diphosphonate (99mTc-HDP) a marked regional focal increase in radioactivity was identified in the medullary cavity of the left femur. Radiographically there was a corresponding focal increase in bone opacity in the middiaphysis of the left femur. Histopathologically, a 5cm area of bone matrix was present in the diaphysis of the left femur and confirmed as an enostosis-like lesion. Enostosis-like lesi...
Webb AI, Weaver BM.The density of the following equine tissues was measured: white and grey brain matter, myocardium, lung parenchyma, liver, spleen, gastrointestinal tract and contents, renal medulla and cortex, muscle, fat, tendon and bone. Statistical analysis indicated that there were highly significant differences in the values for density between horses and between tissues within horses. Values for density of eight different muscles were obtained for 18 horses and these were shown to differ highly significantly between horses and between muscles within horses. The values for splenic density differed highly...
Schröter C, Bielefeld M, Bielefeld D, Macke C, Winkelmann C, Mommsen P, Krettek C, Zeckey C.The upper limb is one of the most frequently injured body regions in equestrian sports, but it is unclear which injuries are involved, and there are no data on the associated accident mechanism. The present study is aimed at evaluating the accident mechanisms, injuries of the upper limbs, and the circumstances of the accident in equestrian sports. We included 218 patients who were all treated between 2006 and 2014 at the level I trauma center at the Medical University in Hannover because of equestrian-related accidents. The most frequent injuries were fractures and bruising in the shoulder ...
Soana S, Gnudi G, Bertoni G, Botti P.The aim of this study is to point out the time of appearance of the carpal and tarsal bones in the fetal horse, considering an estimated fetal age, to follow their morphological development through to birth, and to characterize possible abnormal shape and/or delay of their ossification. The right carpal and tarsal region of 140 equine fetuses of both sexes (71 males, 69 females) and different ages (from 70 to 340 days of gestation) were examined radiographically in order to identify the sites of ossification from their earliest appearance. The times of appearance of the sites of ossification o...
Nishita T, Matsushita H.Sections of equine thymus were examined for the presence of carbonic anhydrase (CA) isozymes by an immunohistochemical method. Carbonic anhydrase III, a major enzyme of skeletal muscle, was localized in some of the epithelial-reticular cells of the equine thymus. This finding suggests the presence of a new type of cell in the thymic cortex. The concentration of CA-III in the thymus was 17 micrograms/g wet tissue. CA-I and CA-II were not found in equine thymus.
Moll HD, Slone DE, Humburg JM, Jagar JE.Three horses and three ponies were treated for traumatic luxation of the proximal intertarsal or tarsometatarsal joint. In each case, there were fractures of one or more tarsal bones. Three of the animals had disruption of one of the collateral ligaments. Five animals were treated by closed reduction and external coaptation. One pony was treated by open curettage, a cancellous bone graft, and cast immobilization. No internal fixation was used in any of these animals. From this series of cases, it would appear that closed reduction and external coaption alone is adequate treatment for most case...
Les CM, Stover SM, Willits NH.Paired metacarpi obtained at necropsy from 100 horses ranging in age from term fetus to 35 years were examined to estimate the prevalence and sites of metacarpal fusion. Metacarpal fusion was seen in 192 of 200 metacarpi, and 78% of all horses 2 years or older had 2 or more fusions. Fusion of the second metacarpal bone to the third metacarpal bone was significantly (P < 0.001) more common than was fusion of the fourth to the third metacarpal bone. Fusions appeared for the most part in pairs and were bilaterally symmetric. Rooney-Prickett type-A carpometacarpal joint configurations (in which...
Ainsworth DM, Ducharme NG, Hackett RP, Eicker SW, Snedden K.We examined the electromyographic activity of the costal portion of the diaphragm and the transverse abdominal and external oblique muscles in 6 chronically instrumented awake adult horses during eupneic breathing, during 2 levels of hypercapnia (fractional concentration of inspired CO2; FICO2 = 0.4 and 0.6), and during 2 levels of hypocapnic hypoxia (FIO2 = 0.15 and 0.12). Using the inert gas technique, we also measured the end-expiratory lung volumes of the 6 horses during eupnea, 6% CO2 challenge, and 12% O2 breathing. During eupneic breathing, phasic electrical activity of these 3 muscles ...
Speirs VC, Anderson GA, Bourke JM.The efficacy of treating carpal lesions by arthrotomy was evaluated in 210 Thoroughbred racehorses, using survival analysis to compare their racing performances and earnings with those of 840 control horses. The treated horses were significantly inferior with respect to races contested, and wins plus places (P less than 0.001) and races won (P less than 0.01). There was no difference with respect to earnings (P less than 0.1); after adjusting for other factors, arthritis, site of fracture and presence of a displaced chip had no effect on racing performance in horses with a single-site lesion i...
Parth RA, Svalbe LS, Hazard GH, Church S.Two cases of severe scapulohumeral osteoarthritis in Miniature ponies are described, one bilateral and the other unilateral. The condition is thought to occur in miniature breeds as a result of scapulohumeral dysplasia. The presentation in one of the ponies was unusal: it refused to pick up either fore limb, with progression to a uniquely bizarre gait with narrow forelimb placement, an arched back and widely placed hindlimbs camped well forward under the body. The other pony was presented for an acute unilateral non-weight bearing forelimb lameness. Response to analgesia in both cases was poor...
Nuchprayoon N, Ritruechai P, Watchararat K, Limroongruengrat W, Wongtawan T, Arya N.Hippotherapy in patients with neuromuscular dysfunction creates high focal pressure on the pony's back due to bareback riding and an asymmetrical riding position. This study aimed to investigate the acute effect of asymmetrical bareback riding on the pony's spinal kinematics, blood lactate, serum creatine kinase, heart rate, and temperament score. Eight ponies were selected, and they were walked on a treadmill for 45 min on each experimental day, including warm-up (5 min), weight-loading by mannequin (30 min), and cool-down (10 min) sessions. During the weight-loading session, three different ...
Kotzé SH.The muscle layers of the ileocaecal junctions of horses (n = 18), plains zebras (Equus burchelli antiquorum) (n = 3), mountain zebras (Equus zebra zebra) (n = 2), and a donkey were examined macroscopically and microscopically. The muscular tunic of the ileocaecal papilla was made up of 3 layers: an innermost circular layer which was a continuation of the circular muscle of the ileum, a central longitudinal layer which was a continuation of one part of the longitudinal layer of the ileum and an outermost layer, composed of two collateral semicircular lips, formed by the circular layer of the ca...
Valdez H, Adams OR.After preliminary studies on cadavers, a surgical approach was developed for removal of the medial meniscus, offering maximal exposure and minimal trauma to the articular surfaces of the medial tibial plateau and femoral condyle. Medial meniscectomy was then performed on 10 clinically normal horses that had been given general anesthesia. Nine horses were euthanatized at intervals of 1 to 6 months, and the joints were evaluated grossly and histologically. (One horse will be examined 1 year after surgery). Medial meniscus tears were diagnosed in 5 horses; medial meniscectomy was done on 4 horses...
Lorenz J, Brounts SH.This article reviews the pathology, diagnosis, and treatment of sacroiliac joint injuries. These injuries can be acute or chronic and can involve soft tissue structures surrounding the joint or the bony structures of the joint. The several diagnostic modalities for sacroiliac injuries vary in usefulness and accessibility. Treatment of sacroiliac problems is usually supportive and nonspecific and includes the use of antiinflammatory medications and an appropriate exercise regimen. The prognosis depends on the cause, but severe injuries can limit a horse's future athletic activity.
Voorhout G, Klein WR, Meutstege FJ.An avulsion fracture of the tendon of origin of the extensor digitorum longus muscle is reported in a horse and a cat. This avulsion fracture was due to injury in both animals. There was a striking similarity of radiographic findings in these animals, with involvement of the lateral trochlear ridge and lateral condyle of the femur. The horse was slaughtered because of a poor prognosis as a riding-horse. Fixation of the avulsed fragment with two Kirschner wires resulted in complete recovery in the cat.
Troyer DL, Oyster RO, Hunt MC.The purpose of this study was to find a combination histochemical staining technique for the evaluation of equine skeletal muscle that is reliable and effective, while offering a substantial reduction in the labor and cost involved with currently used individual histochemical methods. Several combinations under varying conditions of pH were studied. The most uniform results were obtained using an acid preincubation step at an optimal pH of 4.2 followed by reduced nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR) and the remainder of the acid-ATPase procedure.
Durchfeld B, Rüdiger J.Bilateral rupture of the musculus longus capitis from the tuberculum musculare of the os occipitale and of the musculus rectus capitis ventralis from the os occipitale combined with a synchondrolysis of the synchondrosis sphenooccipitalis in a 17 months old thoroughbred stallion is reported.
Zakia LS, Palumbo MIP, Teixeira RBC, Resende LAL, Soares MP, de Oliveira-Filho JP, Amorim RM, Borges AS.This article describes the clinical and electromyographic findings of neuromyotonia in a 19-month-old male crossbred Quarter Horse that presented with stiffness and muscle asymmetry in the hind limbs as well as sacrococcygeal, paravertebral, and gluteal myokymia. An electromyographic study showed spontaneous continuous muscle fiber activity with high-frequency discharges, fibrillations, positive sharp waves, fasciculation potentials, and complex repetitive discharges. Histological examination of the gluteal muscle showed a mixed neurogenic and myopathic pattern. The findings are consistent wit...
Löfqvist L, Pinzke S.The horse industry in Sweden has rapidly expanded in recent years. This increasing number of horses implies a greater need for more farriers. Shoeing a horse is hard physical work, and includes awkward work postures and repetitive movements. It is well known that hard physical work increases the risk of injuries and musculoskeletal problems. The risk is especially high for musculoskeletal disorders when certain movements are constantly repeated. Heavy or repeated unilateral loads lead to considerable stress on the muscles, which can lead to rupture and fatigue that can cause long term problems...
Strömberg B.Thermography in veterinary medicine has hitherto been proven to be a method of great value in the detection of orthopaedic lesions in racehorses. Lesions of the musculo-skeletal system affecting tendons, joints, bones and skeletal muscle can be demonstrated and documented at an early stage thereby preventing the development of more serious lesions.
Robinson NE.The primary function of the equine respiratory system is the exchange of oxygen and carbon dioxide at a rate that is matched to metabolism. Gas exchange requires ventilation, distribution of gas within the lung, perfusion of blood through pulmonary capillaries, matching of ventilation and blood flow, diffusion of gases between air and blood, and transport of gases to and from the muscles. In this article, the author reviews what is known about each of these processes in the resting and exercising horse.
Nash RA, Nunamaker DM, Boston R.To evaluate stiffness and bone-pin interface stress for a transcortical tapered-sleeve pin (TSP) that incorporates bilateral tapered sleeves over a transcortical pin. Methods: 14 third metacarpal bones (MCIII) collected from adult horses of various breeds. Methods: Each MCIII was cut in half to provide 2 test specimens. Pins (conventional and TSP) of 3 diameters (6.35, 7.94, and 9.50 mm) were inserted in specimens (3 specimens for each diameter and each type of pin). The test fixture simulated a typical sidebar-span skeletal fixation device for horses. Single cycle load-deflection tests were p...
Long CD, Galuppo LD, Waters NK, Hornof WJ.The aim of this study was to evaluate the diagnostic value of 99mTc-HMPAO leukocyte scintigraphy (LS) by means of a retrospective review of its use in 14 horses that were evaluated for orthopedic infection as a cause of lameness. A total of 17 LS exams were performed in 14 horses. LS studies were positive in 10 of 14 horses. A bacterial infection was confirmed with cytology or culture in 9 of 10 positive horses. Negative LS studies occurred in 4 of 14 horses. Necropsy confirmed the lack of infection in 2 of the 4 horses. Other clinical data and a favorable clinical outcome supported a negative...
