Biochemical development of subchondral bone from birth until age eleven months and the influence of physical activity

Subchondral bone provides structural support to the overlying articular cartilage, and plays an important role in osteochondral diseases. There is growing insight that the mechanical features of bone are related to the biochemistry of the collagen network and the mineral content. In the present study, part of the normal developmental process and the influence of physical activity on biochemical composition of subchondral bone was studied. Water content, calcium content and characteristics of the collagen network (collagen, hydroxylysine, lysylpyridinoline (LP) and hydroxylysylpyridinoline (HP) crosslinking) of subchondral bone were measured in newborn foals, 5-month-old foals (pasture-grown and box-confined) and 11-month-old foals at 2 differently loaded sites of the proximal articular surface of the first phalanx. During the first 5 months postpartum, water and hydroxylysine content decreased significantly while calcium and collagen content and the amount of HP and LP crosslinks increased significantly. The withholding of physical activity during this developmental phase affected the biochemical characteristics of subchondral bone only at the site that is loaded during physical exercise. At this site, calcium content and both HP and LP crosslink levels increased significantly less than in pasture-raised animals. During development from 5-11 months, measured parameters remained essentially constant, except for water content, which decreased further. It is concluded that substantial changes, presumed to be largely exercise-driven, take place during the normal process of development in the biochemical composition of equine subchondral bone. Normal development of subchondral bone is presumably important for the normal functional adaptation of this bone to the loading conditions it is subjected to and therefore essential to resist the future biomechanical challenges the horse will encounter during its athletic career. The findings from this study and the assumed important role of subchondral bone quality in the pathogenesis of osteochondral disease merit more attention to the role of the collagen network in subchondral bone.     

Surgical management of complete diaphyseal third metacarpal and metatarsal bone fractures: Clinical outcome in 10 mature horses and 11 foals

Reasons for performing study: Osteosynthesis of third metacarpal (McIII) and third metatarsal (MtIII) bone fractures in horses is a surgical challenge and complications surrounding the repair are common. Retrospective studies evaluating surgical repair, complications and outcome are necessary to increase knowledge and improve success of long bone fracture repair in the horse. Objectives: To evaluate clinical findings, surgical repair, post operative complications and outcome of 10 mature horses and 11 foals with McIII or MtIII fractures that were treated with open reduction and internal fixation (ORIF). Methods: Medical records were reviewed and follow‐up information obtained by means of radiographs and/or telephone questionnaire. Results: Survival was achieved in 62% of the horses (3 mature/10 foals). On long‐term evaluation (>6 months) 11 horses (2 mature/9 foals) were fit for their intended activity, one mature horse had a chronic low grade lameness, and one foal was lost to follow‐up because it was sold. The main fracture types were simple transverse (33.3%) or simple oblique (28.6%) and 71.4% of the fractures were open, 3 Type I (one mature/2 foals) and 12 type II (7 mature/5 foals). The preoperative assessment revealed inadequate emergency treatment in 10 horses (5 mature/5 foals; 47.6%). Survival rate of horses with open fractures was 12.5% (1/8) in mature and 85.7% (6/7) in foals. Post operative incisional infection (4 mature, 3 foals) was only managed successfully in 2 foals. Fracture instability related to inadequate fracture fixation technique occurred in 4 horses (all mature) and was always associated with unsuccessful outcome. Conclusions: Age, bodyweight and infection are strongly associated with outcome in treatment of complete McIII/MtIII fractures. Clinical relevance: Rigid fixation using plates and screws can be successful in treatment of closed or open, complete diaphyseal McIII/MtIII fractures in mature horses and foals. Instable fixation, infection and a bodyweight >320 kg are major risk factors for unsuccessful outcome.     

Epiphyseal cartilage canal blood supply to the metatarsophalangeal joint of foals

Reasons for performing study: It is presently unknown whether cartilage ischaemia plays any part in the pathogenesis of osteochondral fragmentation within the equine metatarsophalangeal joint, as no detailed studies on microcirculation in the area have been reported. Objective: To describe the developmental pattern of the blood supply to the epiphyseal growth cartilage in the metatarso‐phalangeal joint of foals. Methods: Eight Standardbred foals were sacrificed between birth and age 7 weeks to undergo a barium perfusion procedure to demonstrate vessels within growth cartilage canals of one hindlimb. The metatarso‐phalangeal joint was cleared in methyl salicylate and perfused vessels studied in the intact bones. The bones were sawed into 5 mm thick slabs, decalcified and radiographed. Selected slabs were cleared in methyl salicylate for a second time and examined at low magnification. The dorsal half of the sagittal ridge of the distal third metatarsal bone and the plantar half of the proximal phalanx were examined histologically. Results: Regions of the epiphysis with thick cartilage contained a greater number of perfused vessels than regions with thin cartilage. The cartilage canal vessels were oriented either parallel or perpendicular to the underlying ossification front. Cartilage canal vessels were incorporated into the ossification front during growth and became reliant on a subchondral arterial source. Macroscopically visible lesions were not detected in the current group of foals. On histological examination, pathological changes consisting of an area of chondronecrosis surrounded by fibrovascular granulation tissue were found in sections from the lateral proximo‐plantar eminence of the proximal phalanx in the 7‐week‐old foal. Conclusion: The same anatomical feature (traversing the ossification front to enter cartilage canals) reported to render vessels vulnerable to failure in the tarsus was also present in the metatarso‐phalangeal joint of foals. Potential relevance: Osteochondrosis may occur by the same pathogenetic mechanism in the metatarso‐phalangeal joint as in the tarsus of foals.     

Influence of exercise and joint topography on depth‐related spatial distribution of proteoglycan and collagen content in immature equine articular cartilage

Reasons for performing study: There is ample evidence on topographical heterogeneity of the principal biochemical components of articular cartilage over the surface of the joint and the influence of loading thereon, but no information on depth‐related zonal variation in horses. Objectives: To study depth‐related zonal variation in proteoglycan (PG) and collagen content in equine articular cartilage. Methods: Two techniques (safranin‐O densitometry and Fourier transform infrared spectroscopy) were applied to sections of articular cartilage from the proximal phalangeal bone of the metacarpophalangeal joint of 18‐month‐old Thoroughbreds that had been raised at pasture from age 0–18 months without (PASTEX) and with (CONDEX) additional exercise. Two sites were investigated: site 1 at the joint margin that is unloaded at rest or at slow gaits, but subjected to high‐intensity loading during athletic activity; and site 2, a continuously, but less intensively, loaded site in the centre of the joint. Results: Proteoglycan values increased from the surface to the deep layers of the cartilage, collagen content showed a reverse pattern. PG content was significantly higher at site 2 in both PASTEX and CONDEX animals without an effect of exercise. In the PASTEX animals collagen content was significantly higher at site 1, but in the CONDEX group the situation was reversed, due to a significant exercise effect on site 1, leading to a reduced collagen content. Conclusions: Collagen and PG content gradients agree with findings in other species. The observations on PG levels suggest that the exercise level was not strenuous. The collagen results in the PASTEX group confirmed earlier findings, the lower levels at site 1 in the CONDEX group being possibly due to an advancement of the physiological maturation process of collagen remodelling. Potential relevance: This study confirms earlier observations that even moderate variations in exercise level in early age may have significant effects on the collagen network of articular cartilage.     

Deep erosions of the palmar aspect of the navicular bone diagnosed by standing magnetic resonance imaging

Reasons for performing study: Erosion of the palmar (flexor) aspect of the navicular bone is difficult to diagnose with conventional imaging techniques. Objectives: To review the clinical, magnetic resonance (MR) and pathological features of deep erosions of the palmar aspect of the navicular bone. Methods: Cases of deep erosions of the palmar aspect of the navicular bone, diagnosed by standing low field MR imaging, were selected. Clinical details, results of diagnostic procedures, MR features and pathological findings were reviewed. Results: Deep erosions of the palmar aspect of the navicular bone were diagnosed in 16 mature horses, 6 of which were bilaterally lame. Sudden onset of lameness was recorded in 63%. Radiography prior to MR imaging showed equivocal changes in 7 horses. The MR features consisted of focal areas of intermediate or high signal intensity on T1‐, T2*‐ and T2‐weighted images and STIR images affecting the dorsal aspect of the deep digital flexor tendon, the fibrocartilage of the palmar aspect, subchondral compact bone and medulla of the navicular bone. On follow‐up, 7/16 horses (44%) had been subjected to euthanasia and only one was being worked at its previous level. Erosions of the palmar aspect of the navicular bone were confirmed post mortem in 2 horses. Histologically, the lesions were characterised by localised degeneration of fibrocartilage with underlying focal osteonecrosis and fibroplasia. The adjacent deep digital flexor tendon showed fibril formation and fibrocartilaginous metaplasia. Conclusions: Deep erosions of the palmar aspect of the navicular bone are more easily diagnosed by standing low field MR imaging than by conventional radiography. The lesions involve degeneration of the palmar fibrocartilage with underlying osteonecrosis and fibroplasia affecting the subchondral compact bone and medulla, and carry a poor prognosis for return to performance. Potential relevance: Diagnosis of shallow erosive lesions of the palmar fibrocartilage may allow therapeutic intervention earlier in the disease process, thereby preventing progression to deep erosive lesions.     

Severe bilateral physitis with instability and Salter‐Harris type 1 fractures in two foals

This Case Report describes the clinical, radiographic, computed tomographic and post mortem findings in 2 foals with severe bilateral physitis of the distal third metatarsal bones (MtIII). The foals were admitted because of bilateral hindlimb lameness of several weeks' duration. Initial examination revealed that the physeal regions of the distal MtIII were enlarged, warmer than normal and painful on palpation. Case 1 was treated conservatively and discharged but was readmitted 8 weeks later because of clinical deterioration. In both foals, radiographs showed plantar dislocation of both epiphyses through the physis and a Salter‐Harris type 1 fracture. The foals were subjected to euthanasia and a post mortem examination.     

Training affects the collagen framework of subchondral bone in foals.

Subchondral bone provides structural support to the overlying articular cartilage and plays an important role in osteochondral diseases. There is growing insight that the mechanical features of bone are related to the biochemistry of the collagen network. In this study the effect of exercise on water, calcium and the collagen network (total collagen, lysyl-hydroxylation, hydroxylysylpyridinoline, and lysylpyridinoline crosslinks) of subchondral bone at two differently loaded sites (site 1: intermittently loaded; site 2: constantly loaded) is investigated in foals.Exercise influenced calcium content and levels of both types of crosslinks at site 1, but had no influence on site 2. There was no concomitant increase in lysyl-hydroxylation level with the rise in crosslinks. Levels of lysyl-hydroxylation and lysylpyridinoline crosslinking were lower at site 1 than at site 2. It is concluded that exercise affects the post-translational modifications of the collagen component of subchondral bone. Loading also appears to play a role in site-related topographical differences. The lack of any relation between the sum of pyridinoline crosslinks and the amount of triple helical hydroxylysine gives support to a recent hypothesis that lysyl-hydroxylation of the triple helix and the telopeptides are under separate control.     

Fibro‐osseous tumour of the second metacarpal bone in a Thoroughbred filly

A 7‐month‐old Thoroughbred filly was evaluated because of an enlarging mass present on the proximomedial aspect of the left metacarpus. The mass was first noticed at age 2 months and had continued to increase in size. The mass was firm, nonpainful to palpation, covered with normal haired skin and had never been associated with lameness. Radiographs obtained at ages 2 and 7 months revealed an enlarging and partially mineralised mass associated with the second metacarpal bone. Based on the clinical and radiographic progression, as well as the location of the mass, a poor prognosis for future athletic soundness was given and the filly was subjected to euthanasia. The mass had histological features of both an ossifying fibroma and osteoma.     

Ex vivo calibration and validation of in vivo equine bone strain measures

Reasons for performing study: Data are required to confirm that strain gauges recording high bone strains in Thoroughbred racehorses provide an accurate record of bone strain. Objective: To test the accuracy and reliability of very high in vivo strain recordings made during fast exercise in Thoroughbred racehorses. Methods: Strains were recorded during exercise from rosette gauges implanted onto the mid‐shaft dorsal cortex of each third metacarpal bone (MC3) in 6 yearling and 6 mature Thoroughbreds in a previous experiment. Bulk elastic modulus (E_US) was calculated from ultrasound speed and single photon absorptiometry measures. Each cleaned MC3 with the original gauge in situ and new gauges placed in a region of strain similarity (as shown by photoelastic coating) was loaded in a materials testing system (MTS) and strains recorded during loading. Elastic moduli were calculated from strain measures from new rosette gauges on the medial, dorsal, lateral and palmar surfaces (E_m; E_d; E_l; E_p), and bulk moduli calculated from the displacement of the MTS machine heads during loading (E_bt). Peak loads were increased incrementally to failure. Results: Of 14 original gauges tested against new gauges, 11 recorded strains from 80–115% of the new gauges and 3 showed reduced function (31–40%). E_bt were similar to E_m, and E_US were similar to E_l and not significantly different from E_d. Maximum strains at yield were recorded by the medial gauges and ranged from ?7500 to ?16,000 μ?. Conclusions and clinical relevance: Similarities between recordings from gauges used in vivo and new gauges confirmed the reliability and likely accuracy (or possible underestimate) of very high strains (exceeding ?6000 μ?) recorded in exercising Thoroughbred racehorses. The similarity between E_bt and E_mconfirms that the gauges measured the true distortion of the bone in the MTS. These results confirm that mammalian bone may withstand much greater compressive loads than ?4000 μ? under some conditions at least.     

Osteosarcoma of the middle phalanx in a horse

An 11‐year‐old Thoroughbred gelding was presented for lameness investigation following acute onset hindlimb lameness, which developed during a period of paddock turnout. Clinical examination revealed a swelling over the dorsolateral aspect of the pastern that was painful on digital palpation. Radiography of this area was consistent with an aggressive bone lesion involving both joint surfaces of the middle phalanx with pathological fracture and distal collapse of this bone. On this basis, the horse was subjected to euthanasia. Post mortem histopathological examination revealed presence of an osteosarcoma without involvement of the articular cartilage. This bone tumour is extremely rare in horses and has not been reported in this anatomical location.     

Bullous emphysema with haemorrhage in a premature foal

A Warmblood foal was admitted at one day of age because of prematurity and seizures. Clinical and clinical pathology abnormalities were consistent with prematurity and suspected hypoxic seizures that responded to anti‐convulsive therapy. The foal stabilised after several days of intensive care but then developed an airway infection. Thoracic radiographs showed multiple cavitary lesions and ultrasound examination suggested intra‐cavital haemorrhage. The foal went on to develop septicaemia and was subjected to euthanasia. Post mortem examination revealed multiple bullous emphysema with haemorrhage. This disorder should be considered in the differential diagnosis of foals having air‐fluid filled cavities on thoracic radiographs.     

Surgical thrombectomy in horses with aortoiliac thrombosis: 17 cases

Reasons for performing study: Aortoiliac thrombosis (AIT) is a progressive vascular disease characterised by an exercise‐induced hindlimb lameness. After developing a surgical technique, a follow‐up study was required. Objectives: To assess the surgical results of a surgical thrombectomy in horses with AIT, a chronic arterial occlusive disease of the aorta and its caudal arteries. Methods: Seventeen cases showed the typical signs of AIT and diagnosis was confirmed by Doppler‐ultrasonography. Average age of the horses was 12 years. Seven stallions, 6 mares and 4 geldings were included. Results: The thrombus was located in the left hindlimb (5 cases), the right hindlimb (9 cases) or in both hindlimbs (3 cases). Two cases were operated on both limbs with a few days between surgeries. Nine (53%) horses regained their athletic performance and 2 horses were able to work for at least 30 min without complaint, instead of the initial 5 min prior to surgery. During surgery one horse had to be subjected to euthanasia because the thrombus was too tightly attached to the arterial wall and could not be removed. Two horses were subjected to euthanasia post operatively due to severe myopathy and one due to a femoral fracture during recovery. Two reocclusions of the treated artery occurred 4 months after surgical intervention: one horse was reoperated and, due to the extent of the thrombus and quality of the arterial wall, the horse was subjected to euthanasia; the other horse was subjected to euthanasia without a second surgery. A severe complication was the appearance of AIT in the contralateral limb after surgery as result of occlusion caused by an embolus loosened by the procedure. Post anaesthetic myopathy was seen in 4 (24%) of the cases and could be so severe that euthanasia had to be considered. Conclusion and potential relevance: Surgical intervention by means of a thrombectomy in horses with AIT should be considered; 65% of the horses regained athletic activity and 53% of the operated horses in this study performed at their previous level. Adequate padding, correct positioning, prevention of intraoperative hypotension and keeping surgery time as short as possible, are important parameters to prevent post operative myopathy.     

Congenital bilateral aplasia of the metacarpophalangeal joints in a foal

A 2‐day‐old Warmblood filly was presented for examination of an angular limb deformity of the left front limb and an upright conformation of both metacarpophalangeal joints. Radiological examination revealed bilateral absence of the metacarpophalangeal joint space with fusion of the third metacarpal bone and first phalanx (synostosis). No treatment was undertaken. The filly was readmitted to the clinic 10 weeks later for bilateral front limb lameness. On radiological examination, the synostosis of the front metacarpophalangeal joints was still present. Physitis of the distal growth plate of the right third metacarpal bone and proximal growth plate of the right proximal phalanx, and an avulsion fracture of the palmaromedial and proximal aspect of the left middle phalanx, with a cystic like lesion on the medial aspect of distal first phalanx and proximal middle phalanx were diagnosed. Given the poor prognosis, the foal was subjected to euthanasia. Post mortem examination confirmed the absence of the metacarpophalangeal joint space with a trabecular bony union between the third metacarpal bone and the first phalanx. A rudimentary joint capsule was present at the level of the absent joints as well as a small zone of articular cartilage, which invaginated over a short distance into the dorsal trabecular bone on the right front limb. On the medial aspect of the left proximal interphalangeal joint, a focal defect of articular cartilage with exposure of subchondral bone was observed. This is the first case report of a foal born with congenital aplasia of both metacarpophalangeal joints. Congenital malformations should be considered as differential diagnosis in lame foals or foals born with angular or flexural limb deformities.     

Air sampling in the breathing zone of neonatal foals for prediction of subclinical Rhodococcus equi infection

Reasons for performing the study: Disease caused by Rhodococcus equi is a significant burden to the horse breeding industry worldwide. Early detection of rhodococcal pneumonia, albeit important to minimise treatment costs, is difficult because of the insidious nature of the disease and the lack of definitive diagnostic tests. Objectives: To investigate air sampling from the breathing zone of neonatal foals as a predictor of subsequent rhodococcal pneumonia. Methods: Air samples were collected from the breathing zone of 53 neonatal foals (age ≤10 days) and again at the time of routine ultrasonographic screening for R. equi pneumonia (age 1–2 months). Results: Pneumonia was diagnosed ultrasonographically in 23% of foals. Virulent R. equi was detected in air from the breathing zone of 19% of neonatal foals and 45% of foals at age 1–2 months. There was no association between virulent R. equi in the breathing zone of foals and the subsequent ultrasonographic diagnosis of rhodococcal pneumonia. The median concentration of virulent R. equi in the breathing zone of both neonates (0 [range 0–4] colony‐forming units [cfu]/250 l) and older foals (0 [range 0–3] cfu/250 l) was not significantly different from that in background air samples (0 [range 0–6] cfu/250 l). There was no difference in the concentration of virulent R. equi in the breathing zone of older foals that were diagnosed with rhodococcal pneumonia or clinically normal foals. Conclusion: Detection of virulent R. equi in air from the breathing zone was not a positive predictor of rhodococcal pneumonia in foals up to age ≤2 months. Potential relevance: Selective culture of air samples from the breathing zone of young foals is not better at diagnosing rhodococcal pneumonia than early ultrasonographic screening. However, culture of air samples from the breathing zone of older foals remains a useful herd‐based epidemiological tool.     

Evaluation of serum concentrations of biomarkers of skeletal metabolism and results of radiography as indicators of severity of osteochondrosis in foals

OBJECTIVE: To determine whether serum concentrations of biomarkers of skeletal metabolism can, in conjunction with radiographic evaluation, indicate severity of osteochondrosis in developing horses. ANIMALS: 43 Dutch Warmblood foals with varying severity of osteochondrosis. PROCEDURE: 24 foals were monitored for 5 months and 19 foals were monitored for 11 months. Monthly radiographs of femoropatellar-femorotibial and tibio-tarsal joints were graded for osteochondral abnormalities. Serial blood samples were assayed for 8 cartilage and bone biomarkers. At the end of the monitoring period, foals were examined for macroscopic osteochondrosis lesions. RESULTS: Temporal relationships were evident between certain serum biomarkers and osteochondrosis severity in foals during their first year. Biomarkers of collagen degradation (collagenase-generated neoepitopes of type-II collagen fragments, type-I and -II collagen fragments [COL2-3/4C(short)], and cross-linked telopeptide fragments of type-I collagen) and bone mineralization (osteocalcin) were positive indicators of osteochondrosis severity at 5 months of age. In foals with lesions at 11 months of age, osteochondrosis severity correlated negatively with COL2-3/4C(short) and osteocalcin and positively with C-propeptide of type-II procollagen (CPII), a collagen synthesis marker. Radiographic grading of osteochondrosis lesions significantly correlated with macroscopic osteochondrosis severity score at both ages and was strongest when combined with osteocalcin at 5 months and CPII at 11 months. CONCLUSIONS AND CLINICAL RELEVANCE: The ability of serum biomarkers to indicate osteochondrosis severity appears to depend on stage of disease and is strengthened with radiography. In older foals with more permanent lesions, osteochondrosis severity is significantly related to biomarker concentrations of decreased bone formation and increased cartilage synthesis.     

Haematogenous septic arthritis in foals: Short‐ and long‐term outcome and analysis of factors affecting prognosis

Synovial sepsis represents a major cause of morbidity and mortality in foals; however, there are no studies focusing on foals particularly at risk during the first 2 months of life. Our objective was to analyse outcome in foals aged <2 months with haematogenous septic arthritis and to identify prognostic factors and compare the effects of two different lavage procedures on outcome. Sixty foals with synovial sepsis were used for our retrospective study in which medical records, online data and telephone interviews were utilised to analyse prognostic factors, and determine short‐ and long‐term survival and athletic performance of foals treated at Evidensia Equine Specialist Hospital, Helsingborg, between 2008 and 2014. Overall survival to discharge was 80% (48/60). Time to long‐term follow‐up ranged from 6 months to 6.5 years. Forty/60 (67%) horses survived long‐term. Four/8 (50%) of the nonsurvivors at long‐term follow‐up had been subjected to euthanasia due to sequelae of joint sepsis. Of the long‐term survivors, 37/40 (92.5%) achieved athletic soundness. Overall long‐term outcome for athletic soundness was 37/60 (62%). Prognostic factors based on historical, clinical or laboratory data, or the use of through‐and‐through needle lavage compared to endoscopic lavage as the first procedure, could not be identified. The present study demonstrates a more favourable prognosis than previously reported, with 80% of foals with synovial sepsis surviving to discharge, and approximately 60% achieving athletic soundness. However, the study was limited by a small population size, which may account for the failure to verify statistically significant prognostic factors.     

Pedal bone fractures

Fractures of the pedal bone are usually the result of direct trauma, and are relatively commonly encountered in equine practice. Either front or hind feet may be affected. Seven distinct fracture types are recognised. Type I fractures involve the palmar/plantar process and do not enter the distal interphalangeal (DIP) joint. Type II fractures are oblique or parasagittal fractures that are articular but are not on the midline. Type III fractures are midline articular fractures that bisect the pedal bone into 2 equal halves. Type IV fractures involve the extensor (pyramidal) process of the pedal bone. Type V fractures are comminuted and split the pedal bone into multiple fragments. Type VI fractures are solar margin fractures. Type VII fractures are exclusive to foals and are also fractures of the solar margin. In most cases the onset of clinical signs is acute. The diagnosis is usually achieved by radiography, although computed tomography or magnetic resonance imaging can be helpful in some cases. Treatment options include surgical and nonsurgical therapies. The prognosis for articular fractures (Types II and III) is worse than for nonarticular fractures (Types I, IV, VI and VII) because of the likelihood of osteoarthritis within the DIP joint. Nonarticular fractures carry a good prognosis if a long enough convalescence is undertaken. Comminuted fractures (Type V) carry a poor, but not hopeless, prognosis.     

Pharmacokinetics of butorphanol and evaluation of physiologic and behavioral effects after intravenous and intramuscular administration to neonatal foals

Background: Despite frequent clinical use, information about the pharmacokinetics (PK), clinical effects, and safety of butorphanol in foals is not available. Objectives: The purpose of this study was to determine the PK of butorphanol in neonatal foals after IV and IM administration; to determine whether administration of butorphanol results in physiologic or behavioral changes in neonatal foals; and to describe adverse effects associated with its use in neonatal foals. Animals: Six healthy mixed breed pony foals between 3 and 12 days of age were used. Methods: In a 3‐way crossover design, foals received butorphanol (IV and IM, at 0.05 mg/kg) and IV saline (control group). Butorphanol concentrations were determined by high‐performance liquid chromatography and analyzed using a noncompartmental PK model. Physiologic data were obtained at specified intervals after drug administration. Pedometers were used to evaluate locomotor activity. Behavioral data were obtained using a 2‐hour real‐time video recording. Results: The terminal half‐life of butorphanol was 2.1 hours and C₀ was 33.2 ± 12.1 ng/mL after IV injection. For IM injection, C_max and T_max were 20.1 ± 3.5 ng/mL and 5.9 ± 2.1 minutes, respectively. Bioavailability was 66.1 ± 11.9%. There were minimal effects on vital signs. Foals that received butorphanol spent significantly more time nursing than control foals and appeared sedated. Conclusions and Clinical Importance: The disposition of butorphanol in neonatal foals differs from that in adult horses. The main behavioral effects after butorphanol administration to neonatal foals were sedation and increased feeding behavior.     

Septic pyomyositis,multiple pelvic osteomyelitis and thrombosis in a Thoroughbred foal

Multiple septic osteomyelitis, septic thrombi and septic arthritis are recognised as possible complications of sepsis; however, there are few reports of localised pyomyositis in association with septic arterial thrombosis in foals. A 1-month Thoroughbred colt was presented for investigation of acute and progressive left hindlimb lameness. Physical and laboratory examinations were performed. Ultrasonographic, radiographic and computed tomographic examinations revealed the presence of multiple abscesses and areas of osteomyelitis localised to the gluteal muscles, coxal bone and lumbar spine respectively. Considering the poor prognosis, the foal was subjected to euthanasia. Necropsy confirmed the diagnostic imaging findings and revealed the presence of an extensive septic thrombus, affecting the internal iliac artery, and a single pulmonary abscess. Streptococcus equi subsp. zooepidemicus was isolated from all lesions.