Isolation of Ross River virus from mosquitoes and from horses with signs of musculo-skeletal disease

OBJECTIVE: To report clinical and clinicopathological findings in horses naturally infected with Ross River virus (RRV) and identify likely mosquito arbovirus vector species. PROCEDURES: Veterinarians submitted serum samples from 750 horses because they suspected Ross River virus (RRV) infection. The samples were tested for the presence of IgM and IgG antibody to RRV and for the presence of virus. Mosquitoes were trapped, differentiated to species level and tested for the presence of RRV by virus isolation. RESULTS: RRV was isolated from six species of mosquitoes (Ochlerotatus camptorhyncus, Culex globocoxitus, Cx. australicus, Cx. annulirostris, Cx. quinquefasciatus, Anopheles annulipes) and from 13 horses with clinical signs of musculo-skeletal disease. Antibody to RRV was detected in 420 of the 750 serum samples; 307 contained IgG only; 76 contained both IgM and IgG and 37 contained only IgM antibody to RRV. Virus was isolated from horses with IgM antibody only. CONCLUSIONS: RRV can be isolated from infected horses during the short time period when there is an overlap of clinical signs, positive IgM serology and viraemia. Early spring infections of horses may occur if RRV infected mosquito vectors are present. RRV has not been shown to cause clinical disease in horses. This is the first report of isolation of RRV from Oc. camptorhyncus in the Murray region and indicates a potential for infection of humans and animals in autumn as well as in spring.     

Disease suspected to be caused by Ross River virus infection of horses

Ross River Virus (RRV) was believed to be the cause of acute illness in four horses around the Bellarine peninsula in south-west Victoria, Australia. The horses presented with clinical signs including petechial haemorrhages, lymphadenopathy, distal limb swelling and reluctance to move. Fibrinogen was also elevated in three of the four horses. Whilst no virus was isolated, serological testing revealed elevated RRV IgM titres in all horses indicating acute infection. The outbreak occurred at a time when a known RRV vector, the mosquito Aedes camptorhynchus was recorded at very high levels in the region. This report is one of very few to attribute specific signs of disease to RRV in horses in conjunction with serological evidence of infection. Aust Vet J 2008;86:367-370.     

Ross River Virus Infection of Horses: Appraisal of Ecological and Clinical Consequences

Ross River virus (RRV) is a mosquito-borne arbovirus of the genus Alphavirus that causes disease in humans and horses in Australia. A temporal association of RRV infection in horses with clinical signs including pyrexia, malaise, and polyarthralgia has been reported, along with reduced athletic performance, often for extended periods. Despite these reports, disease due to RRV remains somewhat controversial as experimental infection of horses has resulted in obvious viraemia yet minimal signs of clinical disease. The relatively high viraemia demonstrated by horses infected with RRV has led to speculation that they could act as an important reservoir host of the virus, although this remains unclear. This review sought to appraise the existing literature relating to RRV infection of horses and to summarize the ecological and clinical consequences of RRV of relevance to the equine industry and to public health more broadly.     

Polymerase chain reaction tests for the identification of Ross River, Kunjin and Murray Valley encephalitis virus infections in horses

OBJECTIVE: To develop and validate specific, sensitive and rapid diagnostic tests using RT-PCR for the detection of Ross River virus (RRV), Kunjin virus (KV) and Murray Valley encephalitis virus (MVEV) infections in horses. METHODS: Primer sets based on nucleotide sequence encoding the envelope glycoprotein E2 of RRV and on the nonstructural protein 5 (NS5) of KV and MVEV were designed and used in single round PCRs to test for the respective viruses in infected cell cultures and, in the case of RRV, in samples of horse blood and synovial fluid. RESULTS: The primer pairs designed for each of the three viruses amplified a product of expected size from prototype viruses that were grown in cell culture. The identity of each of the products was confirmed by nucleotide sequencing indicating that in the context used the RT-PCRs were specific. RRV was detected in serums from 8 horses for which there were clinical signs consistent with RRV infection such that an acute-phase serum sample was taken and submitted for RRV serology testing. The RRV RT-PCR was analytically sensitive in that it was estimated to detect as little as 50 TCID50 of RRV per mL of serum and was specific in that the primer pairs did not amplify other products from the 8 serum samples. The RRV primers also detected virus in three independent mosquito pools known to contain RRV by virus isolation in cell culture. Samples from horses suspected to be infected with KV and MVEV were not available. CONCLUSION: Despite much anecdotal and serological evidence for infection of horses with RRV actual infection and associated clinical disease are infrequently confirmed. The availability of a specific and analytically sensitive RT-PCR for the detection of RRV provides additional opportunities to confirm the presence of this virus in clinical samples. The RT-PCR primers for the diagnosis of KV and MVEV infections were shown to be specific for cell culture grown viruses but the further validation of these tests requires the availability of appropriate clinical samples from infected horses.     

Clinical screening of horses and early warning for West Nile virus

Clinical presentation of West Nile disease in horses is variable, but ataxia, weakness and muscle fasciculations are often observed, sometimes with abnormal behaviour, teeth grinding and bruxism. Practitioners should be aware that horses are more sensitive to infection than man and serve as sentinels for an early warning of West Nile virus circulation in a given area. This early warning allows the implementation of preventive and control measures such as vaccination of horses and mosquito control.     

The experimental infection of horses with Murray Valley encephalitis and Ross River viruses

Eleven weanling horses were inoculated with Murray Valley encephalitis and Ross River viruses either by intravenous injection or by the bite of Culex annulirostris or Aedes vigilax mosquitoes infected orally. Five of the 11 horses circulated trace amounts of MVE virus for 1 to 5d and they infected 7/408 Cx annulirostris which subsequently fed on them. Haemagglutination-inhibiting antibody persisted at detectable levels for the 24-week observation period. With Ross River virus, only one of 11 horses inoculated developed a viraemia detectable by inoculation of suckling mice but 5 horses contained virus sufficient to infect 41/383 Cx annulirostris that fed on them 3 to 4 days after inoculation. On primary inoculation with Ross River virus, only 2 horses developed HI antibody but late responses occurred in 3 horses following probable naturally acquired re-infections. With both viruses, most horses remained normal, some developed mild pyrexia and transient clinical signs. This paper, therefore, indicates that horses are unlikely to be efficient amplifiers of either MVE or RR viruses and does little to incriminate them as important pathogens.     

A serological survey of cattle in the Thames-Coromandel district of New Zealand for antibodies to Ross River virus

AIM: To determine if cattle exposed to the southern saltmarsh mosquito (SSM), Aedes camptorhynchus, in the Thames-Coromandel district of New Zealand had been exposed to Ross River virus (RRV).

METHODS: A purposive sampling design was used to test cattle from seven farms located in close proximity to four sites infested with A. camptorhynchus in the Thames-Coromandel district. Sera from 207 cattle were tested for antibodies to RRV, using an ELISA and confi rmatory virus neutralisation test (VNT) as the gold standard.

RESULTS: All 207 cattle tested negative for antibodies to RRV using the ELISA and VNT.

CONCLUSIONS: This study found no evidence of exposure to RRV in cattle in locations in the Thames-Coromandel district of New Zealand where populations of SSM were present.     

Comparison of owner-reported health problems with veterinary assessment of geriatric horses in the United Kingdom

Reasons for performing study: Previous studies suggest that owners underestimate or incorrectly recognise or report health problems in geriatric horses. However, few studies have directly compared owner‐reported and veterinary assessed disease. Objectives: To compare the findings of veterinary clinical examination of geriatric horses with owner‐reported clinical signs and disease. Methods: A total of 200 horses aged ≥15 years were randomly selected to receive a veterinary examination, from responses to a cross‐sectional postal questionnaire survey. Veterinary examinations were performed within 2 months of questionnaire return, and agreement between owner‐reported data and veterinary clinical findings was assessed. Results: Owners under‐reported many clinical signs and disease conditions detected on veterinary clinical examination. For example, dental abnormalities (detected in 95.4% of horses, reported by 24.5% of owners); cardiac murmurs (detected in 20% of horses, reported by 0.5% of owners); lameness (present in 50% of horses, reported by 23% of owners) and hoof abnormalities (detected in 80% of horses, reported by 27% of owners). Agreement between owner‐reported and veterinary assessed respiratory disease (Kappa 0.02–0.2), body condition score (Kappa 0.24) and coat abnormalities (Kappa 0.42) was poor, fair and moderate, respectively. Range of motion (ROM) of the tarsal and metacarpophalangeal joints was lower in horses with owner‐reported osteoarthritis (P = 0.005 and <0.001, respectively). Conclusions and potential relevance: The low prevalence and relatively poor agreement of owner‐reported disease compared to that detected on veterinary examination suggests inaccurate or under‐recognition, or inaccurate reporting of health problems by owners of geriatric horses, which could lead to a delay in presentation for veterinary treatment. Increased veterinary involvement and improved owner education in the care of geriatric horses should facilitate earlier identification of disease, particularly that which is not readily detectable by owners, and aid management of health and welfare problems.     

Australian Stringhalt--epidemiological, clinical and neurological investigations

An investigation of 78 cases of typical Australian Stringhalt from 52 properties in Victoria was carried out from 1985 to 1987. Horses were either examined in the field (n = 52), referred to the Veterinary Clinical Centre (n = 13) or clinical details were obtained verbally (n = 13). In addition 10 cases of false or atypical stringhalt were examined. Detailed soil and pasture analysis was carried out on 14 properties where Australian Stringhalt had occurred. Information was also obtained on epidemiology of the condition from a survey of practitioners. Fifty of the 52 cases examined in the field occurred in horses that were dependent upon poor quality unimproved dry pasture. In all but a few cases, there was no pasture improvement or fertiliser application, leading to the development of weed-dominated pastures, particularly by flatweed, Hypochaeris radicata. The range of clinical signs exhibited by horses with Australian Stringhalt was described and a grading system proposed to classify horses according to severity of signs. Laryngeal abnormalities were present in 10 of 11 cases examined endoscopically and these horses exhibited increased electromyographic (EMG) activity in the long digital extensor muscle at rest and during hindlimb flexion. To a large extent, the EMG changes disappeared and digital extensor muscle atrophy improved in two horses that were monitored to recovery. Deep peroneal nerve conduction studies in four horses with Australian Stringhalt showed a substantial reduction in nerve conduction velocity and when stimulated at 50 Hz were unable to sustain activation of the long digital extensor muscle. EMG and evoked responses appeared to be sensitive indicators of the state of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical assessment and grading of back pain in horses

BackgroundThe clinical presentation of horses with back pain (BP) vary considerably with most horse''s willingness to take part in athletic or riding purpose becoming impossible. However, there are some clinical features that are directly responsible for the loss or failure of performance.ObjectivesTo investigate the clinical features of the thoracolumbar region associated with BP in horses and to use some of the clinical features to classify equine BP.MethodsTwenty-four horses comprised of 14 with BP and 10 apparently healthy horses were assessed for clinical abnormality that best differentiate BP from normal horses. The horses were then graded (0–5) using the degree of pain response, muscular hypertonicity, thoracolumbar joint stiffness and overall physical dysfunction of the horse.ResultsThe common clinical features that significantly differentiate horses with BP from non-BP were longissimus dorsi spasm at palpation (78.6%), paravertebral muscle stiffness (64.3%), resist lateral bending (64.3%), and poor hindlimb impulsion (85.7%). There were significantly (p < 0.05) higher scores for pain response to palpation, muscular hypertonicity, thoracolumbar joint stiffness and physical dysfunction among horses with BP in relation to non-BP. A significant relationship exists between all the graded abnormalities. Based on the cumulative score, horses with BP were categorized into mild, mild-moderate, moderate and severe cases.ConclusionsBP in horse can be differentiated by severity of pain response to back palpation, back muscle hypertonicity, thoracolumbar joint stiffness, physical dysfunctions and their cumulative grading score is useful in the assessment and categorization of BP in horses.     

Hendra Virus Infection in Horses: A Review on Emerging Mystery Paramyxovirus

Hendra virus (HeV) is a zoonotic paramyxovirus which causes acute and deadly infection in horses (Equus caballus). It is a rare and unmanaged emerging viral infection in horses which is harbored by bats of the genus Pteropus (Australian flying foxes or fruit bats). The virus is pleomorphic in shape and its genome contains nonsegmented negative-stranded RNA with 18234 nucleotides in length. The virus is transmitted from flying foxes to horses, horse to horse, and horse to humans. Human-to-human transmission of HeV infection is not reported yet. The infection of HeV in horses is highly variable and shows broad range of signs and lesions including distinct respiratory and neurological disorders. Currently, there are no specific antiviral drugs available for the treatment of HeV infection in horses. Vaccination is considered as prime option to prevent HeV infection in horses. A subunit vaccine, called as “Equivac HeV vaccine” has been approved recently for preventing this viral infection in horses. In addition, a plethora of common preventive strategies could help restrict the inter- and intra-species transmission of HeV. Considering the scanty but severe fatality cases of this mystery virus as well as lack of proper attention by veterinary scientists, this review article spotlights not only on the clinical signs, transmission, epidemiology, biology, pathogenesis, and diagnosis of HeV but also the preventive managements of this uncommon infection in horses by vaccination and other precautious strategies.     

Association of owner-reported noise with findings during dynamic respiratory endoscopy in Thoroughbred racehorses

Reasons for performing study: To determine the association between owner‐reported noise and findings during dynamic respiratory endoscopy (DRE) in a large case series. Hypothesis: The sensitivity of owner‐reported noise for dynamic upper respiratory tract obstructions in horses is low, and the specificity is high. Methods: One hundred horses underwent DRE for the investigation of abnormal respiratory noise and/or poor performance. The association of abnormal noise with findings during DRE was evaluated. Results: Eighty‐five horses underwent DRE for the investigation of abnormal respiratory noise. Of these, 82% were found to have one or more obstructive upper respiratory tract abnormalities during DRE. Forty‐eight percent of horses reported to gurgle, rattle or make a rough noise were diagnosed with solitary palatal dysfunction. A further 24% with this history showed palatal dysfunction in combination with an additional abnormality. Twenty‐seven percent of horses with a history of whistling or roaring showed some degree of recurrent laryngeal neuropathy. Seven percent of horses with a history of whistling or roaring had vocal cord collapse as a solitary condition, whereas 40% had vocal cord collapse and another abnormality. The sensitivity of abnormal respiratory noise for any obstruction of the upper portion of the respiratory tract was high (84%), while the specificity was low (25%). Characteristic owner reported noise patterns showed moderate to low sensitivity for specific conditions. Whistling and roaring showed the highest specificity (≥80%) for laryngeal dysfunction. Conclusion: Diagnosis of upper respiratory tract obstructions based solely on owner‐reported noise and performance history may result in incomplete diagnoses. Clinical relevance: DRE should be performed in horses with abnormal respiratory noise to rule out complex conditions of the upper portion of the respiratory tract.     

A survey on the use of rugs in Australian horses

The practice of horse rugging has important implications for horse welfare and performance, but in Australia, rugging practices have not been properly documented. The objective of this study was to obtain an understanding of Australian horse rugging practices. An online survey reviewed the management of 2659 Australian horses over 12 months. Of the reported horses a total of 84.8% were rugged, although most owners (69.5%) indicated that they were unsure whether horses needed to be rugged at all. Rugging was felt by 59.8% of owners to be a requirement for horses in competition. Riding and competition were significantly associated with the use of rugs. Nearly all respondents (89.0%) felt that ‘over-rugging’ was a concern. However, 4.8% of owners would use up to 4 rugs at any one time on their horse and 21.4% of horses were still rugged in temperatures above 20°C in Australia. Many Australian horse owners (42.8%) also believe that horses feel cold if they are not rugged. Anthropomorphism when it comes to rugging horses cannot be justified as the horse has a much wider thermoneutral zone (TNZ) than humans. Australian climate, owner opinions, equestrian discipline and whether a horse is used for riding influence Australian horse rugging practices. However, current practices are based on limited available research and are not necessarily to the benefit of the horse. The major limitation was that the survey likely attracted respondents who are interested in the topic creating a self-selection bias.     

Acute and chronic oxalate toxicity in Miniature Horses associated with soursob (Oxalis pes‐caprae) ingestion

Over the period of 11 years (2004–2015) 14 miniature horses in six separate outbreaks presented with clinical signs consistent with acute or chronic oxalate toxicity. All animals had access to Oxalis pes‐caprae or soursob. Miniature horses with acute oxalate toxicity and hypocalcaemia had muscle fasciculations, tremors and synchronous diaphragmatic flutter; these horses responded to treatment with intravenous and oral calcium. Chronic oxalate toxicity was associated with ill‐thrift, stiffness, enlarged heads, kyphosis and neurological signs. These animals had normal serum calcium concentrations, but increased serum alkaline phosphatase activity. Radiographs indicated that affected animals had bones that were osteopenic, often with pathological fractures. Bones that were examined histologically showed increased osteoclastic and osteoblastic activity, consistent with nutritional secondary hyperparathyroidism and fibrous osteodystrophy. These animals were treated, with mixed success, with oral calcium supplementation. A palatability trial showed that horses will readily eat soursobs, and measured total oxalate concentrations in soursobs collected from five different properties ranged from 13.5 to 18.5%. The presentation of affected animals with either acute hypocalcaemia or nutritional secondary hyperparathyroidism, together with a history of grazing soursobs, suggest that acute and chronic oxalate toxicity are the cause of the clinical signs seen in affected miniature horses.     

Evaluation of high-speed treadmill videoendoscopy for diagnosis of upper respiratory tract dysfunction in horses

OBJECTIVE: To evaluate high-speed treadmill videoendoscopy as a diagnostic technique and document the abnormalities found in Australian horses referred for poor performance associated with abnormal upper respiratory tract noise but where a definitive diagnosis could not be made at rest. DESIGN: A retrospective clinical study using client-owned horses. PROCEDURE: The clinical records and videorecordings of all horses referred to the University of Sydney for poor performance associated with abnormal upper respiratory tract noise during a 13-month period were examined. Only horses with a normal physical examination including absence of lameness, and where a definitive diagnosis of the cause of the abnormal upper respiratory tract noise could not be made from the resting videoendoscopic examination were included in the study. The age, gender, breed of horse and the purpose for which the horse was used were ascertained from the record and videorecordings were reviewed by the authors and any abnormalities noted. RESULTS: There were 37 horses included in the study. An upper airway abnormality was identified during high-speed treadmill videoendoscopy in 73% of horses. One abnormality was identified in 22 horses, 2 abnormalities in 4 horses and 3 abnormalities in 1 horse. Abnormalities identified included laryngeal hemiparesis (n = 15), axial deviation of the aryepiglottic folds (n = 10), pharyngeal collapse (n = 3), dorsal displacement of the soft palate (n = 2), epiglottic collapse (n = 1), axial deviation of the vocal cord (n = 1) and laryngeal collapse (n = 1). CONCLUSIONS: The results of this study are similar to reports from overseas and suggest high-speed treadmill videoendoscopy appears to be a useful technique to diagnose the cause of upper airway dysfunction in Australian horses referred specifically for poor performance associated with abnormal upper respiratory noise. However, a diagnosis will not be made in all horses undergoing this procedure. There were five horses with two or three abnormalities none of which were apparent at rest. This would suggest that in all horses making abnormal upper respiratory noise associated with poor performance, even where an abnormality is identified at rest, high-speed treadmill videoendoscopy should be performed for a complete diagnosis.     

An outbreak of the equine rhabdomyolysis syndrome in a racing yard

An outbreak of muscle stiffness and poor performance among 59 thoroughbreds at a Newmarket flat racing yard was investigated between the beginning of May and the end of June 1986. Over a third of the horses showed signs of muscular stiffness, and 38 had, at one or more of the sampling times, creatine kinase (CK) activities above 200 iu/litre and, or, aspartate aminotransferase (AST) activities above 300 iu/litre when they were sampled six to eight hours after exercise. The following season, at a similar time and stage of training, only four of 39 horses sampled had CK activities between 200 and 300 iu/litre, and three had AST activities between 500 and 600 iu/litre. Plasma samples from 18 animals sampled at the start of the investigation and 13 days later were tested for the presence of antibodies to equine herpesvirus (EHV). Ten of them showed a response highly suggestive of an EHV-1 infection. No significant abnormality was found in the fractional electrolyte values from seven randomly selected animals. Unusually high numbers of normally sized and stained fibres with centrally placed nuclei as well as groups of small muscle fibres were found in muscle biopsies taken from three animals which continued to have high enzyme activities and show recurrent signs of muscle stiffness.     

Pulmonary ultrasonographic abnormalities associated with naturally occurring equine influenza virus infection in standardbred racehorses

The purpose of this investigation was to determine if naturally occurring acute infectious upper respiratory disease (IRD) caused by equine influenza virus is associated with ultrasonographically detectable pleural and pulmonary abnormalities in horses. Standardbred racehorses were evaluated for signs of IRD, defined as acute coughing or mucopurulent nasal discharge. For every horse with IRD (n = 16), 1 or 2 horses with no signs of IRD and the same owner or trainer (n = 30) were included. Thoracic ultrasonography was performed within 5-10 days of the onset of clinical disease in horses with IRD. Horses without IRD were examined at the same time as the horses with IRD with which they were enrolled. The rank of the ultrasound scores of horses with IRD was compared to that of horses without IRD. Equine influenza virus was identified as the primary etiologic agent associated with IRD in this study. Mild lung consolidation and peripheral pulmonary irregularities were found in 11 (69%) of 16 of the horses with IRD and 11 (37%) of 30 of control horses. Lung consolidation (median score = 1) and peripheral irregularities scores (median score = 1) were greater in horses with IRD compared to horses without IRD (median score = 0; P < .05). Pleural effusion was not observed. Equine influenza virus infection can result in abnormalities of the equine lower respiratory tract. Despite the mild nature of IRD observed in this study, lung consolidation and peripheral pulmonary irregularities were more commonly observed in horses with clinical signs of IRD. Further work is needed to determine the clinical significance of these ultrasonographic abnormalities.     

Ventriculocordectomy as the sole treatment for recurrent laryngeal neuropathy: long-term results from ninety-two horses

OBJECTIVE: To evaluate the effect ventriculocordectomy (VC) for treatment of recurrent laryngeal neuropathy (RLN) on exercise performance and owner satisfaction in a mixed-breed population of horses. STUDY DESIGN: Retrospective study. ANIMALS: Adult horses (n=92) with a history of abnormal respiratory noise and RLN. METHODS: Retrospective analysis of horse that had unilateral VC (and contralateral ventriculectomy in 63 horses) for treatment of idiopathic RLN. Owners/trainers completed a questionnaire about complications and outcome at least 1 year after surgery. Performance index was determined using race records for previously raced Thoroughbreds to evaluate outcome. RESULTS: Clinical signs included abnormal exercise-induced respiratory noises (noises; 52%), poor performance (11%), and noises and poor performance (37%). The median preoperative resting endoscopic grade of laryngeal function was Havemeyer grade III.1 (mild asymmetry). No discharge from the laryngotomy 1 week postoperatively occurred in 62% horses, 22% coughed after surgery, 66% made no noises, 9% continued to make noises at the canter, 21% made noise at the gallop, and 4% of owners were unsure whether noises were present. Ninety-three percent of horses returned to full work after surgery. Overall, 86% of owners considered the surgery worthwhile, 3% did not consider it worthwhile, and 11% were unsure. Surgery had a significantly beneficial effect on the racing performance index in Thoroughbreds (P=.004). CONCLUSIONS: VC is a useful alternative to laryngoplasty for selected cases of RLN and is associated with a positive effect on exercise performance, a low postoperative complication rate, and a high rate of owner satisfaction. CLINICAL RELEVANCE: Unilateral VC should be considered as a sole treatment in horses with low grades of RLN.     

Scintigraphic abnormalities of the pelvic region in horses examined because of lameness or poor performance: 128 cases (1993-2000)

OBJECTIVE: 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. DESIGN: Retrospective study. ANIMALS: 128 horses. PROCEDURE: 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 clinically relevant areas of ARU, follow-up information was obtained through telephone interviews with owners and trainers and analysis of race records. RESULTS: Areas of ARU were identified in the tuber coxae (25 horses), ischiatic tuber (9), hip joint (10), third trochanter (10), ilium (5), sacral tuber region (22), greater trochanter (1), cranial femoral cortex (1), skeletal muscle surrounding the pelvis (34), or multiple areas (11). In 44 horses, areas of ARU were associated with the primary cause of lameness; in 51, areas of ARU were not associated with the primary cause of lameness; and in 33, the primary cause of lameness was not determined. Thirty-six of the 44 horses with clinically relevant areas of ARU were available for follow-up; 15 (42%) had a good outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that pelvic scintigraphy may be useful in identifying abnormalities in horses with hind limb lameness or poor performance.