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.
Swanstrom MD, Stover SM, Hubbard M, Hawkins DA.To determine the relative contributions of the muscles, tendons, and accessory ligaments to the passive force-length properties of the superficial (SDF) and deep digital flexor (DDF) myotendinous complexes. Methods: 8 cadaveric forelimbs from 6 adult Thoroughbreds. Methods: In vitro, limb configurations during slack position and myotendinous lengths during subsequent axial loading of forelimbs were recorded before and after transection of accessory ligaments. Expressions were derived to describe the force-length behavior of each muscle, tendon, and accessory ligament-tendon unit; linear stiffn...
Carstanjen B, Amory H, Youssao I, Remy B.The purpose of this study was to validate an equine-specific osteocalcin (OC) radioimmunoassay (RIA) for use in donkeys and to establish age-related changes in serum OC concentrations in healthy donkeys. Serial dilutions of donkey serum showed parallelism with standard curves obtained with the equine-specific OC RIA. There was a tight linear regression between donkey serum OC values obtained with the equine specific OC RIA and a commercially available bovine-specific OC RIA. Serum OC levels of 27 healthy donkeys, analysed with the equine-specific OC RIA, showed a tight negative logarithmic reg...
van Ginneken MM, Keizer HA, Wijnberg ID, van Dam KG, Schaart G, de Graaf-Roelfsema E, van der Kolk JH, van Breda E.To investigate whether protein kinase C (PKC) isoforms are expressed in equine skeletal muscle and determine their distribution in various types of fibers by use of immunofluorescence microscopy. Methods: 5 healthy adult Dutch Warmblood horses. Methods: In each horse, 2 biopsy specimens were obtained from the vastus lateralis muscle. Cryosections of equine muscle were stained with PKC isoform (alpha, beta1, beta2, delta, epsilon, or zeta)-specific polyclonal antibodies and examined by use of a fluorescence microscope. Homogenized muscle samples were evaluated via western blot analysis. Results...
Davenport-Goodall CL, Ross MW.To identify scintigraphic abnormalities in the pelvic region of horses examined because of hind limb lameness or poor performance and determine the clinical relevance of areas of abnormal radiopharmaceutical uptake (ARU) in these horses. Methods: Retrospective study. Methods: 128 horses. Methods: Medical records were reviewed, and information on signalment, history, admitting complaints, physical examination findings, and results of lameness examinations was recorded. Clinical relevance of areas of ARU was determined by comparison with results of other diagnostic tests. For horses with clinica...
Erichsen C, Eksell P, Widström C, Berger M, Holm KR, Johnston C.The sacroiliac region in 33 clinically normal riding horses was examined with scintigraphy to determine the normal scintigraphic appearance, to evaluate a semiquantitative method used to calculate a sacroiliac joint (SI joint) ratio, and to identify factors that affect the scintigraphic appearance of the pelvis. The scintigraphic examination included dorsal views of each SI joint region and one lateral view of the urinary bladder. Two predefined areas (the SI joint and the area between the tuber sacrale and the SI joint) were evaluated subjectively by comparing the intensity in each area to th...
Cavani F, Fini M, de Terlizzi F, Cadossi M, Ciminelli L, Ortolani S, Cherubini R, De Aloysio D, Giavaresi G, Cadossi R, Canè V.Osteoporosis involves alterations, not only in density, but also in the architectural organisation of the bone; in particular, trabecular orientation, following the skeletal load directions, lends a high degree of stiffness to the whole bone. We investigated the relationship between trabecular orientation, density, stiffness and ultrasound (US) propagation in two orthogonal directions (par. = parallel to, and ort. = orthogonal to the main orientation of the trabeculae) in cylindrical equine bone specimens (thoracic vertebrae) where a preferential orientation is present. A total of 15 cylinders...
Garcia T, Hornof WJ, Insana MF.The strong dependence of tendon echogenicity on insonation angle is explored by analyzing echo spectra. Combining echo spectra with high-resolution images from several modalities reveals that fluid spaces surrounding fascicles and bundles are likely sources of ultrasonic scatter. Mathematical models of tendon structure are proposed to explain how the anisotropic microstructure of tendon gives rise to angle-dependent echogenicity. Echo spectra from spontaneously damaged equine tendon samples were compared with normal equine tendon and found to exhibit a dramatic decrease in anisotropic properti...
Stephen JO, White NA, McCormick WH, Cowles RR, Corley KT.To identify the types of injuries sustained by horses that competed in steeplechase races and determine the prevalence of and risk factors for those injuries. Methods: Prospective study. Methods: 2,680 horses that competed in various types of steeplechase races from 1996 through 2000. Methods: Data regarding races; environment; equipment problems; the number of horses that entered, started, and finished races; the number of riders that fell; and the number of horses that were slowed or stopped by the rider, ran off the course, fell, and sustained injuries or physical abnormalities during races...
Sod GA, Martin GS.To compare the biomechanical properties of a prototype intramedullary pin-plate (IMPP) implant specifically designed for equine metacarpophalangeal (MCP) arthrodesis with a dynamic compression plate (DCP) system. Methods: In vitro biomechanical testing of paired cadaveric equine forelimbs with a simulated traumatic disruption of the suspensory apparatus, stabilized by one of two methods for MCP arthrodesis. Methods: Twenty-one pairs of adult equine cadaveric forelimbs. Methods: Each forelimb had the distal sesamoidean ligaments severed to create a disrupted suspensory apparatus. For each forel...
McClure SR, Van Sickle D, White MR.Extracorporeal shock waves have been used for 30 years to fragment uroliths for nonsurgical treatment for urolithiasis in humans. Applied to bone, shock waves delivered at the appropriate energy and pulse number, can stimulate osteogenesis. In Europe, shock waves are routinely used to treat nonunions in humans despite poor understanding of the mechanism of action. Shock wave therapy has also been used clinically in horses. Preliminary experimental studies indicate that shock wave therapy does not damage soft tissue in the distal aspect of the equine limb and can stimulate osteogenesis througho...
Da Costa Gómez TM, Radtke CL, Kalscheur VL, Swain CA, Scollay MC, Edwards RB, Santschi EM, Markel MD, Muir P.To determine whether bone microcracks are altered after application of focused and radial extracorporeal shock wave therapy (ESWT) to the equine distal limb. Methods: An ex vivo experimental model. Methods: A contralateral limb specimen was obtained from 11 Thoroughbred racehorses with a unilateral catastrophic injury. Distal limb specimens were also obtained from 5 non-racing horses. Methods: Three separate skin-covered bone segments were obtained from the mid-diaphysis of the metacarpus (MC3) or metatarsus (MT3). Focused (9,000 shockwaves, 0.15 mJ/mm2, 4 Hz) and radial (9,000 shockwaves, 0.1...
Lacombe VA, Hinchcliff KW, Devor ST.To characterize insulin-sensitive glucose-transporter (GLUT-4) protein in equine tissues and determine effects of exercise and glucose administration on content of GLUT-4 protein in equine skeletal muscle. Methods: Tissue samples from 9 horses. Methods: Western blot analyses were performed on crude membrane preparations of equine tissues to characterize GLUT-4. In a crossover, randomized study, horses were strenuously exercised for 3 consecutive days and then administered 13.5% glucose or isotonic saline (0.9% NaCl; control) solution, i.v., at similar infusion rates for 12.1 hours. Samples wer...
Eto D, Yamano S, Mukai K, Sugiura T, Nasu T, Tokuriki M, Miyata H.We hypothesize that high intensity training for Thoroughbred horses that have been subjected to conventional training could further improve the metabolic properties of the middle gluteal muscle. Nine well-trained horses were subjected to high intensity (80-100% Vdot;O(2)max, 5 minx2) training for 12 weeks. Biopsy samples were obtained from the muscle before and after 4 and 12 weeks of training. Three of the 9 horses did not complete the training programme. In the remaining 6 horses, activities of succinic dehydrogenase (SDH), phosphofructokinase (PFK) and 3-hydroxy acyl CoA dehydrogenase (HAD)...
Jackson BF, Lonnell C, Verheyen K, Wood JL, Pfeiffert DU, Price JS.Injuries to the skeleton are a major cause of morbidity and mortality in racehorses and age, gender and season have all been shown to influence risk of injury. Objective: To use biochemical markers of bone cell activity to establish to whether cellular processes in bone underlie these described effects. Methods: Blood samples were collected monthly from 2-year-old horses in race training between November 1998 and September 1999. Mean age at the start of the study was 20 months (range 18-23 months), with no significant difference in average age between colts (n = 84) and fillies (n = 63). Three...
Eto D, Yamano S, Kasashima Y, Sugiura T, Nasu T, Tokuriki M, Miyata H.Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals. Objective: Well-controlled exercise could improve muscle potential ability for endurance running. Methods: Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in...
Edwards JG, Newtont JR, Ramzan PH, Pilsworth RC, Shepherd MC.Dantrolene sodium (Dantrium) has been used extensively for the treatment of myopathies in man and anecdotal evidence suggests it is of clinical benefit in the control of exercise-induced rhabdomyolysis (ER) in racehorses, although data to support this are currently lacking. Objective: To investigate the efficacy of oral dantrolene sodium in controlling ER in a randomised, double-blind, placebo-controlled crossover trial involving 77 Thoroughbred racehorses in Newmarket, UK. Methods: Horses were treated on 2 occasions 1 week apart, with treatment days coinciding with a return to exercise follow...
Le Jeune SS, Macdonald MH, Stover SM, Taylor KT, Gerdes M.Objective-To determine whether partial transection of the medial branch of the suspensory ligament (MBSL) alters equine third metacarpal bone (MC3) condylar surface strains and forelimb, distal joint angles in a manner consistent with promotion of lateral condylar fracture. Study Design-In vitro biomechanical experiment. Sample Population-Right forelimbs from 7 Thoroughbred horse cadavers. Methods-Lateral and medial MC3 condylar, dorsal and abaxial, bone surface strains and distal joint angles were measured both before and after partial transection of the MBSL during in vitro axial limb compre...
Suwannachot P, Verkleij CB, Van Weeren PR, Everts ME.We studied the effects of exercise without or with a subsequent period on pasture on Ca2+ ATPase concentration in foal skeletal muscle, and compared the results with those previously reported on Na+, K+ ATPase. Ca2+ ATPase was measured in homogenates as Ca2+-dependent steady-state phosphorylation from [gamma-32P]ATP. From day 7 after birth, 24 foals were divided into three groups: (i) staying in a box stall (Box); (ii) staying in a box stall with an exercise programme of an increasing number of sprints per day (Exercise); and (iii) staying on pasture (Pasture). Half of the foals (12 with four ...
Nollet H, Van Ham L, Verschooten F, Vanderstraeten G, Deprez P.To determine the usefulness of magnetic motor-evoked potentials (MMEPs) for assessing the integrity of the cervical, thoracic, and thoracolumbar spinal cord in horses with bilateral hind limb ataxia. Methods: 9 horses and 1 donkey with bilateral hind limb ataxia of various degrees. Methods: The motor cortex was stimulated magnetically, and MMEPs were recorded bilaterally from the extensor carpi radialis and cranial tibial muscles. Results: In 5 horses and 1 donkey, MMEPs with normal onset latencies and peak-to-peak amplitude were recorded from the extensor carpi radialis muscles, whereas abnor...
Lehnhard RA, McKeever KH, Kearns CF, Beekley MD.There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4-8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate-polyacrylamide gel e...
Pinchbeck GL, Clegg PD, Proudman CJ, Stirk A, Morgan KL, French NP.A prospective cohort study was conducted on horses starting in hurdle and steeplechase races on six UK racecourses in 2000 and 2001. Trainers or carers were questioned on the horses' pre-race routine and observational data were collected in the stables and parade ring. Some practices were common to many starters, such as withholding food and water before racing whereas other practices, such as schooling frequency, were more variable. There was a total of 2879 starts and a total of 83 injuries or medical events (28.8/1000 starts). The commonest types of injury were tendon/suspensory injuries an...
Nout YS, Hinchcliff KW, Jose-Cunilleras E, Dearth LR, Sivko GS, DeWille JW.To determine the effect of a single bout of exercise and increased substrate availability after exercise on gene expression and content of the glucose transporter-4 (GLUT-4) protein in equine skeletal muscle. Methods: 6 healthy adult Thoroughbreds. Methods: The study was designed in a balanced, randomized, 3-way crossover fashion. During 2 trials, horses were exercised at 45% of their maximal rate of oxygen consumption for 60 minutes after which 1 group received water (10 mL/kg), and the other group received glucose (2 g/kg, 20% solution) by nasogastric intubation. During 1 trial, horses stood...
Jackson BF, Blumsohn A, Goodship AE, Wilson AM, Price JS.Studies in humans have found circadian changes to be one of the most important sources of controllable preanalytical variability when evaluating bone cell activity using biochemical markers. It remains unclear whether similar circadian changes influence bone marker concentrations in the horse. The aim of this study was to characterize changes in serum concentrations of three biochemical markers of bone cell activity over a 24-h period in six 2-yr-old Thoroughbred mares, and to determine circadian variability in IGF-I, which regulates bone turnover. Three bone markers were measured in serum: os...
Redden RF.Radiographic examination of the equine foot can provide the veterinarian and farrier with a wealth of information. Positioning and selection of exposure factors are of central importance if one is to produce radiographs of maximum diagnostic value.
Parks A.The list of possible diagnoses derived from matching anatomic structures or tissues to pathologic processes is inevitably broad in nature. Understanding and observation of distal limb function, conformation, and balance is the basis of identifying where the greatest abnormal stresses within the distal limb are likely to occur. This is key to focusing the diagnostic process and, in some instances, to treating the horse when a definitive diagnosis cannot be achieved.
Clayton HM, Hobbs SJ, Rhodin M, Hernlund E, Peterson M, Bos R, Bragança FS.Prior to international competitions, dressage horses are evaluated for fitness to compete while trotting in hand on a firm surface. This study compares the kinematics of experienced dressage horses trotting under fitness-to-compete conditions vs. performing collected and extended trot when ridden on a sand-fiber arena surface. The hypotheses are that the vertical range of motion (ROM) and left-right asymmetries in minimal and maximal heights of axial body segments at ridden trot exceed those when trotting in hand. Inertial measurement units (IMUs) attached mid-dorsally to the head, withers, an...
Nagy A, Dyson SJ.There is no description of comparative magnetic resonance imaging (MRI) and fan-beam computed tomography (CT) findings in the fetlock of lame sports horses. Objective: To document low-field MRI and fan-beam CT diagnoses in the lame and nonlame limbs of sports horses with fetlock region pain, and to evaluate whether combined imaging provides superior information to either technique alone. Methods: Retrospective descriptive study. Methods: Clinical records of sports horses with pain causing lameness localised to the metacarpo/metatarsophalangeal joint region that had undergone fan-beam CT and lo...
Boado A, Pollard D, Dyson S.There is limited information about the orthopaedic health of dressage horses. This study aimed to document the orthopaedic status, lesion distribution, and evolution of injuries in 70 horses undergoing a minimum of five in-depth orthopaedic assessments at six-months' intervals. Warmblood (70.0%) and Iberian (24.3%) breeds predominated. The median lameness grade at initial examination was 2/5 (interquartile range 2,2; range 0,3). Hypermetria (42.9%) or hypermetria and weakness (12.9%) were observed at the initial examination and did not change over time. Metacarpophalangeal/metatarsophalangeal ...
Wubulikasimu M, Liu J, Yao X, Meng J, Wang J, Zeng Y, Li L, Ren W.Kazakh horses, a distinguished breed in China known for their dual-purpose use in milk and meat production, exhibit early maturation, tolerance to coarse feeding, and strong resistance to environmental stress. However, the gene expression differences across various muscle tissues of Kazakh horses have yet to be elucidated. In this study, transcriptomic sequencing was performed on muscle tissues from three anatomical regions of Kazakh horses, including the longissimus dorsi (Gb), external oblique (Gf), and diaphragm (Gg) muscles. In the Gb and Gf groups, 426 differentially expressed genes (DEGs...
Science (New York, N.Y.)August 28, 2025
Volume 389, Issue 6763 925-930 doi: 10.1126/science.adp4581
Liu X, Jia Y, Pan J, Zhang Y, Gong Y, Wang X, Ma Y, Alvarez N, Jiang L, Orlando L.Horsepower revolutionized human history through enhanced mobility, transport, and warfare. However, the suite of biological traits that reshaped horses during domestication remains unclear. We scanned an extensive horse genome time series for selection signatures at 266 markers associated with key traits. We detected a signature of positive selection at -known to be a modulator of behavior in mice-occurring ~5000 years ago (ya), suggesting that taming was one of the earliest steps toward domestication of horses. Intensive selection at began ~4750 ya with the domestication bottleneck, leading ...
Cervantes-Sevilla JR, Ramírez-Cervera M, Guzman-Ruvalcaba MJ.Traumatic hemothorax is a serious condition requiring immediate intervention. We present a case of a 48-year-old male professional jockey who suffered traumatic hemothorax, bilateral pulmonary contusions, and multiple rib fractures after being stomped by a horse. Management included intercostal drainage placement, costal fixation from the 5th to the 10th rib, and intensive care unit admission. Postoperative complications included, acute kidney injury, rhabdomyolysis, and severe acute respiratory distress syndrome. This case highlights the importance of a multidisciplinary approach in managing ...
Bierau J, Cruz AM, Koch C, Manso-Diaz G, Büttner K, Staszyk C, Röcken M.Cone-beam computed tomography (CBCT) is regarded as a convenient and suitable alternative to conventional computed tomography. However, in the horse, the quality of obtained data sets needs to be evaluated. Therefore, the aim of this study was to compare the visibility and accessibility of clinically relevant anatomical structures displayed in CBCT and conventional multidetector computed tomography (MDCT). Unassigned: Twenty-nine limbs from horses euthanized for reasons unrelated to this study were used. Native and intraarticular contrast scans of the fetlock (CBCT vs. MDCT) were performed. Th...
Zaha C, Schuszler L, Dascalu R, Nistor P, Florea T, Rujescu C, Sicoe B, Igna C.The field of veterinary medicine lacks information on equine thermal hoof printing, and few data on the same subject are available in dogs. In human medicine, thermography is used to detect heat emitted by the foot when it comes in contact with a flat surface to detect the abnormalities of the foot balance. The hypothesis states that the thermal pattern of the hoof print in Warmblood horses is detectable and it does not vary among the four limbs in leisure and cross-country Warmblood horses in terms of mean temperature of the hoof print surface. A pilot study was conducted to investigate the a...
Zabek T, Bugno M, Klukowska-Rötzler J, Uhlmann B, Gerber V, Słota E.The research article focuses on identifying the locations of five horse genes related to the development of the skeletal and nervous systems. Sequence Analysis and Bacterial Artificial Chromosome (BAC) Library […]
Etemadi F, Tabatabaei Naeini A, Aminlari M.Minerals play vital roles in physiologic processes. Calcium, phosphorus and magnesium are common minerals. Secretion, absorption and homeostasis of these minerals are affected by associations between the active vitamin D and parathyroid hormone (PTH). The aim of this study was to assess concentrations of vitamin D, PTH and minerals, such as calcium, phosphorus and magnesium in horse sera, as well as associations of these values with lameness in horses. In the references, the reasons for lameness can be deficiency and imbalance of minerals, and clinical observations also confirm this and there ...
Minami Y, Kawai M, Migita TC, Hiraga A, Miyata H.Although high oxygen consumption in skeletal muscle may result in severe oxidative stress, there are no direct studies that have documented free radical production in horse muscles after intensive exercise. To find a new parameter indicating the muscle adaptation state for the training of Thoroughbred horses, we examined free radical formation in the muscle by using electron paramagnetic resonance (EPR). Ten male Thoroughbred horses received conventional training for 18 weeks. Before and after the training period, all horses performed an exhaustive incremental load exercise on a 6% incline tre...
Aleman M, Davis E, Knych H, Guedes A, Smith F, Madigan JE.Intrathecal lidocaine hydrochloride under general anesthesia has been used as an alternative method of euthanasia in equids. Carnivore, scavenger, and even human consumption of horse meat from carcasses have been anecdotally reported in rural areas after this method of euthanasia. The presence of drug residues in horse meat has not been investigated. Objective: To investigate if drug residues are found in horse tissues and determine their concentrations. Methods: Of 11 horses requiring euthanasia for medical reasons. Methods: Prospective descriptive study. Horses were anesthetized with total I...
McCarrel TM.Angular limb deformities are common in foals; however, the importance of the deformity and if treatment is required depend on the degree of deformity relative to normal conformation for stage of growth, the breed and discipline expectations, age, and response to conservative therapies. This article addresses the importance of the foal conformation examination to determine which foals need surgical intervention to correct an angular deformity and when. Techniques for surgical growth retardation include the transphyseal staple, screw and wire transphyseal bridge, and transphyseal screw. Appropri...
Sønnichsen HV, Kristoffersen J, Falk-Rønne J.Joint mice in the horse is a wellknown condition, but during the last years diagnosed with increasing frequency. Ethiology and prognosis thus become of major interest. 53 cases of mice in the fetlock are examined and divided in 3 groups on the basis of localization and appearance. On one group characterised by a localization in the plantar aspect of the joint and clearly separated from the tuberosites of the first phalanx histological investigations were carried out resulting in the statement that the mice can be the result of osteochondrosis. Surgical intervention in cases with clinical sympt...
Kirker-Head CA, Loeffler D, Held JP.Malignant melanoma in a 21-year-old, gray, Arabian gelding was manifested by rapidly deteriorating lameness of the right pelvic limb. A melanotic, cutaneous mass of small dimensions was identified in the left jugular furrow. Exploratory laparoscopy revealed widespread infiltration of melanotic masses into the structures of the abdominal cavity. Necropsy indicated the lameness to have resulted from infiltration of neoplastic cells into the sacral nerves, dorsal root ganglia, proximal ischiatic nerve, and gluteal muscle fibers. The primary tumor could not be identified.
Castelijns HH.Domesticated horses need hoof care, because it is rare for wear and growth of the hooves to be in perfect equilibrium. During the shoeing interval, the hoof grows downwards and forward in the direction of the horn tubules, losing some degree of angle. Few horses have perfect limb conformation. The shape of a hoof of a limb with conformation defects adapts in a predictable way. If, for therapeutic or performance reasons, the hoof-shoe combination is modified, there is a not a lot of leeway in the trim of a particular foot, whereas the applied shoe type, placement, and adjustments provide endles...
Kędzierski W, Kowalik S, Mojsym W, Janczarek I, Tkaczyk E.Development of the musculoskeletal system occurs, in part, through an impact on regulatory proteins, such as activin A and decorin. Activin A induces atrophic effects on skeletal muscle, and decorin regulates the formation of connective tissue proteins like collagen and elastin in tendons and ligaments. The aim of this study was to evaluate the influence of different intensities of exercise on blood plasma activin A and decorin concentrations in horses. Ten young purebred Arabian horses were subjected to routine training sessions on a racetrack, and another 11 adult horses of the same breed pa...
Becht JL, Park RD, Kraft SL, Steyn PF, Wrigley RH.Effective radiographic interpretation requires a veterinarian who is knowledgeable of equine limb anatomy and the various principles that affect the resulting image. The normal and its variations must be recognized and understood before the abnormal can be confidently identified as pathologic. Proper patient positioning and sound radiographic technique are mandatory if reliable diagnostic radiographs are to be produced. This review emphasizes equine foot radiographic variations of normal and pseudolesions that occur with commonly used radiographic views performed in equine practice.