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Topic:Case Reports

Case reports in equine medicine provide detailed accounts of individual horses' clinical presentations, diagnostic processes, treatments, and outcomes. These reports are valuable for documenting rare conditions, novel treatment approaches, or unique clinical insights that may not be captured in larger studies. By focusing on individual cases, these reports contribute to the broader understanding of equine health and disease management. They often include comprehensive information on the horse's history, clinical findings, diagnostic tests, therapeutic interventions, and follow-up evaluations. This page assembles peer-reviewed case reports and scholarly articles that explore diverse aspects of equine health, offering insights into specific medical scenarios and their implications for veterinary practice.
A Closed Reduction of Cervical Spine Subluxation in an Arabian Foal with an External Neck Stabilizer.
Animals : an open access journal from MDPI    January 23, 2025   Volume 15, Issue 3 doi: 10.3390/ani15030325
Domańska-Kruppa N, Stefanik E, Wierzbicka M, Kleinpeter A.Cervical spine injuries that impact young horses and foals can result in mild to severe neurological signs or even result in sudden death. There are only a few reports on conservative treatment options for this condition in the scientific literature. If the condition is left untreated, it can lead to the development of degenerative joint disease, resulting in chronic neurological symptoms and discomfort. We present the case of a two-day-old Arabian foal that showed signs of ataxia following a neck injury, being the result of cervical spine subluxation. Radiological examination revealed a dislo...
Ethylene glycol toxicosis in 39 sport horses following ingestion of contaminated water: A case report.
Journal of equine veterinary science    January 2, 2025   Volume 145 105343 doi: 10.1016/j.jevs.2025.105343
Daradics Z, Bungărdean D, Lupșan AF, Popescu M, Bulmez O, Ciulu-Angelescu V, Chelaru VF, Morar I, Mircean M, Cătoi C, Tripon MA, Crecan CM.Ethylene glycol toxicosis is a common occurrence in dogs and cats but has been reported in other species as well. Up to date, only one case of ethylene glycol toxicosis has been described in horses, and specific guidelines for treating ethylene glycol intoxication in this species are not available. Here we describe the case of 39 sport horses that ingested water contaminated with ethylene glycol. The main clinical sign was apathy, but more severely affected individuals also developed abdominal pain and laminitis. Treatment was initiated around 24 h after the exposure, using ethanol as an antid...
Severe auricular skin necrosis as potential postanaesthetic complication in a horse undergoing general anaesthesia for orthopaedic surgeries.
Veterinary anaesthesia and analgesia    December 28, 2024   S1467-2987(24)00416-1 doi: 10.1016/j.vaa.2024.12.004
Schiele AR, Valletti C, Ringer SK.A Trotter mare (aged 5 years 8 months) presented with severe thoracic limb lameness 2 years after screw fixation of a third carpal bone fracture. Septic arthritis of the intermediate carpal joint necessitated three anaesthetics: two arthroscopic lavages in dorsal recumbency, followed by a computed tomography-guided screw explantation with curettage of an infected, sclerotic third carpal bone in right lateral recumbency. For each anaesthetic, maintenance was with isoflurane carried in oxygen and air, and a medetomidine constant rate infusion. Twelve days after the third anaesthetic, the horse h...
Electrochemotherapy with bleomycin for bilateral ocular squamous cell carcinoma in a horse.
Veterinary ophthalmology    December 16, 2024   doi: 10.1111/vop.13310
Larsen MME, Eriksson A, Impellizeri JA.To describe the procedure and outcome of electrochemotherapy (ECT) with bleomycin as a first-line treatment for bilateral ocular surface squamous neoplasia (OSSN) in the eye of a horse. Methods: A client-owned 5-year-old Haflinger gelding with limbal-conjunctival squamous cell carcinoma. Methods: During general and local anesthesia, injection of bleomycin in the ocular tumor was followed by electroporation, applied with a 15 mm needle electrode, needles held parallel to the ocular surface. Results: Treatment with ECT resulted in therapeutic electric pulses and complete tumor response with no...
Electrochemotherapy with bleomycin for bilateral ocular squamous cell carcinoma in a horse.
Veterinary ophthalmology    December 16, 2024   doi: 10.1111/vop.13310
Larsen MME, Eriksson A, Impellizeri JA.To describe the procedure and outcome of electrochemotherapy (ECT) with bleomycin as a first-line treatment for bilateral ocular surface squamous neoplasia (OSSN) in the eye of a horse. Methods: A client-owned 5-year-old Haflinger gelding with limbal-conjunctival squamous cell carcinoma. Methods: During general and local anesthesia, injection of bleomycin in the ocular tumor was followed by electroporation, applied with a 15 mm needle electrode, needles held parallel to the ocular surface. Results: Treatment with ECT resulted in therapeutic electric pulses and complete tumor response with no...
Successful management of two horses with suspected pulmonary haemorrhage in recovery from general anaesthesia.
Veterinary anaesthesia and analgesia    December 16, 2024   doi: 10.1016/j.vaa.2024.11.002
Hordle T, Ranninger E, Bettschart-Wolfensberger R.A 24 year old warmblood mare (case 1) and a 12 year old Holsteiner gelding (case 2) were anaesthetized for bursoscopy and phacoemulsification, respectively. Both were premedicated with intramuscular acepromazine (30 μg kg-1). The horses were sedated with intravenous (IV) medetomidine (7-9 μg kg-1 to effect), before anaesthetic induction with ketamine-diazepam. Anaesthesia was maintained with isoflurane in a mixture of oxygen and medical air, alongside a medetomidine constant rate infusion at 3.5 μg kg-1 hour-1. In recovery, 3 and 5 μg kg-1 of medetomidine were administered IV to cases 1 an...
Birth of a Healthy Monozygotic Twin Foal with Hydrops and a Dead Co-Twin.
Veterinary sciences    December 13, 2024   Volume 11, Issue 12 649 doi: 10.3390/vetsci11120649
Peere S, Van den Branden E, Broothaers K, Polfliet E, Smits K, Govaere J.Transfer of in vitro-produced (IVP) equine embryos is associated with a higher incidence of monozygotic multiple pregnancies, but this remains a rarity. The outcome of monozygotic twin gestation is poor, and good management techniques are lacking. In addition, hydrops conditions are exceptional in horses, with hydroallantois occurring more frequently than hydramnion. Most hydrops conditions will lead to compromise or death of the foal and mare. A 6-year-old multiparous standardbred recipient mare, 332 days pregnant, diagnosed with a monozygotic twin and hydrops with a dead co-twin, gave birth ...
Bilateral coxofemoral dysplasia in a Mangalarga Marchador foal.
Journal of equine veterinary science    December 4, 2024   Volume 144 105253 doi: 10.1016/j.jevs.2024.105253
Kneipp MLA, Sousa LN, Cota LO, Malacarne BD, Winter IC, Santana CH, Santos RL, Xavier ABS, Faleiros RR, Carvalho AM.Coxofemoral dysplasia is a condition characterized by the abnormal development and flattening of the femoral head and deformities in the acetabulum, leading to joint instability. Although described in various animal species, it is uncommon and rarely reported in horses. This article presents a case of incapacitating coxofemoral dysplasia diagnosed in a four-month-old foal Mangalarga Marchador, which exhibited lameness in the hind limbs, thoracolumbar kyphosis, gluteal muscle atrophy, and pronounced sensitivity during pelvic limb flexion. The clinical diagnosis indicative of bilateral coxofemor...
[Equine piroplasmosis: Case descriptions and overview of the epidemiological situation in Europe with focus on Germany].
Tierarztliche Praxis. Ausgabe G, Grosstiere/Nutztiere    December 4, 2024   doi: 10.1055/a-2457-5516
Axt CW, Springer A, von Luckner J, Naucke TJ, Müller E, Strube C, Schäfer I.Equine piroplasmosis (EP) is caused by (.) and (.) and is transmitted by hard ticks. Predominantly, the Mediterranean region is known as being endemic for both pathogens in Europe. However, autochthonous infections in central European countries such as Germany can no longer be ruled out due to individual case reports in horses without any stays abroad as well as the geographical expansion of the habitats of different tick species. The case reports presented underline the risk of infection for horses travelling to endemic areas and in horses imported from such areas to non-endemic countries...
[Equine granulocytic anaplasmosis (EGA): Case description and overview of the epidemiological situation with focus on Germany].
Tierarztliche Praxis. Ausgabe G, Grosstiere/Nutztiere    December 4, 2024   Volume 52, Issue 6 352-360 doi: 10.1055/a-2418-6540
Axt CW, Springer A, Besse A, Naucke TJ, Müller E, Strube C, Schäfer I.Equine granulocytic anaplasmosis (EGA) is a tick-borne disease caused by Anaplasma (A.) phagocytophilum. In Central, Northern, Western, and Eastern Europe, ticks of the Ixodes (I.) ricinus/I. persulcatus complex, in Germany mainly I. ricinus, are considered as vectors. Ixodes ricinus ticks show peaks of activity during the spring and summer months, particularly April to July. Changing climatic conditions, however, have meanwhile led to a year-round risk of tick exposure and thus infections with A. phagocytophilum. The presented case report underlines the seasonal peak phase of the infection ri...
Improved embryo recovery through increased flushing media volume and the impact on unintended pregnancies in a single subject donor mare.
Journal of equine veterinary science    November 29, 2024   105246 doi: 10.1016/j.jevs.2024.105246
Sala-Ayala L, Cuervo-Arango J, Martinez-Bovi R.The case report discusses the implications of using different volumes of flushing media during embryo flushing (EF) procedures in a single donor mare that experienced multiple unintended pregnancies following negative EF outcomes. The study involved two sets of EF experiments over two years on a non-lactating Spanish purebred mare. The initial experiments (group 1, n=6) used 1L of flushing medium (Ringer´s Lactate), and subsequent tests (group 2, n=5) increased the volume to 2L, to assess whether a larger volume could enhance embryo recovery rates. After every EF procedure, no PGF2α was admi...
Generalized sarcoidosis associated with hypertrophic osteopathy in a Standardbred racehorse.
Journal of equine veterinary science    November 28, 2024   Volume 144 105249 doi: 10.1016/j.jevs.2024.105249
Charles A, Kerckhove HV, De Maré L, Cassart D, Ficheroulle J, Pouyade GR, Tosi I.A Standardbred racehorse was presented for exercise intolerance, weight loss, pyrexia and facial deformity. Radiography and ultrasonography revealed periostitis and regional soft tissue swelling of maxillary bones. Computed tomography excluded any dental or sinus origin of these abnormalities. Further deformities on distal limbs and skin lesions appeared during hospitalization. Radiography identified bilateral periostitis and soft tissue swelling in the distal radius and metatarsal bones, as observed in the head, suggestive of hypertrophic osteopathy (HO). Skin biopsies revealed granulomatous ...
Case report: Incomplete bypass ileocolostomy without partial typhlectomy in five horses with acute, non-reducible cecocolic intussusceptions and review of literature.
Frontiers in veterinary science    November 27, 2024   Volume 11 1450395 doi: 10.3389/fvets.2024.1450395
Troillet A, Scharner D.Cecocolic intussusceptions are a rare condition of acute colic in horses requiring immediate surgical intervention due to persistent uncontrollable pain and ongoing ischemic cecal necrosis. Particularly in cases where reduction of the intussusception is surgically not feasible surgical interventions such as partial typhlectomy through colotomy (partial cecal amputation) combined with or without cecal bypass techniques are described. Alternatively, surgical interventions can also be performed without partial typhlectomy via incomplete bypass ileocolostomy. Information regarding applicable techn...
Robinia pseudoacacia poisoning in two horses: A case report.
Veterinarni medicina    November 21, 2024   Volume 69, Issue 11 395-400 doi: 10.17221/55/2024-VETMED
Novotna T, Samonilova E, Klan J, Frgelecova L, Mala A, Svobodova Z, Drabkova Z.This case report describes the poisoning of two mares from the same paddock with Robinia pseudoacacia (Black locust) bark. The poisoning manifested itself by the sudden onset of weakness and fever with transient improvement after the administration of non-steroidal anti-inflammatory drugs and fluids. After the initial stabilisation, the mares were left unattended overnight. One of them was found dead in the morning. The surviving mare developed colic and severe encephalopathy and had to be referred to the clinic. Blood tests revealed severe hyperammonaemia. After four days of symptomatic treat...
Radical surgical excision of extensive perianal melanomas on standing horses: Twenty cases.
Veterinary surgery : VS    November 20, 2024   Volume 54, Issue 2 373-381 doi: 10.1111/vsu.14192
Robert MP, Buyck C, Tricaud C, Cousty M, Pujol R.To report a radical surgical technique for perianal melanomas involving the anal margin in standing horses. Methods: Observational retrospective study. Methods: Twenty client-owned horses presented for surgical excision of extensive (≥4 cm) perianal melanomas. Methods: Demographic data, surgical technique, intraoperative, immediate- and late-postoperative complications were reviewed. Results: All horses (median age 15, Q1-Q3 12 to 17.3 years) were operated under standing sedation and epidural anesthesia. Median hospitalization period was 6.5 days (Q1-Q3 5 to 8.3 days). The anal margi...
Case report: Successful treatment of chorioptic mange in two Belgian draft horse foals with topical ivermectin.
Frontiers in veterinary science    November 20, 2024   Volume 11 1427400 doi: 10.3389/fvets.2024.1427400
Brys M, Den Hondt S, Saey V, Claerebout E, Chiers K.Various draft horse breeds, especially breeds with abundant feathering on the lower limbs, are known to be susceptible to chorioptic mange. Clinical signs of chorioptic mange encompass intense pruritus leading to self-mutilation and hair loss, thickening of the epidermis, and the formation of hyperkeratotic crusts and scabs. Despite the frequent occurrence and high impact of this condition, treatment options are limited, with a conspicuous absence of registered products formulated for equines, and especially foals. This limited availability of approved products highlights the necessity for alt...
Bilateral congenital cystic eye with intraocular tissue differentiation in a horse.
The Journal of veterinary medical science    November 19, 2024   Volume 87, Issue 1 52-56 doi: 10.1292/jvms.24-0285
Sano Y, Miura C, Kinoshita Y, Kakimoto M, Tsuda T, Matsuda K.Congenital cystic eye (CCE) is a rare congenital ocular disease, which has been suggested to be caused by problems with optic vesicle invagination. This is characterized by the formation of intraorbital cystic lesions lined by undifferentiated neuroepithelium. However, cases involving ocular structures with varying degrees of differentiation have also been reported as CCE in humans and animals. In horses, CCE have only been reported as a case presenting as neuroepithelial-lined cysts without the formation of ocular structures. This paper describes large bilateral intraorbital cysts in a 1-day-...
Feed-induced hypersalivation in horses from Austria, Germany and Switzerland.
Equine veterinary journal    November 15, 2024   Volume 57, Issue 4 1035-1043 doi: 10.1111/evj.14433
Böswald LF, Gottschalk C, Kaltner F, Merk J, Schwaiger K, Kienzle E.While previous reports come mostly from the southern Americas, several outbreaks of hypersalivation in horses were observed in Middle Europe from 2016 to 2018. Objective: To describe feed-induced hypersalivation in European horses. Methods: Analysis of feedstuffs. Methods: Veterinarians and horse or stable owners were encouraged to submit feedstuffs from case outbreaks of hypersalivation in which, infectious diseases or other systemic causes of the syndrome were ruled out and intoxication was suspected. Feedstuff analysis was performed, including gross examination, microscopic analysis of fine...
Congenital urachal and urinary bladder defects leading to uroperitoneum in a neonatal quarter horse colt.
The Canadian veterinary journal = La revue veterinaire canadienne    November 4, 2024   Volume 65, Issue 11 1119-1123 
Karam B, Arndt S, Magdesian KG, Cullen T, Dechant JE.A newborn (5 h old) quarter horse colt was presented because of lethargy and severe abdominal distention. Uroperitoneum was suspected during initial workup, based on sonographic imaging and peritoneal fluid analysis. Definitive diagnosis was confirmed during exploratory celiotomy. Surgery revealed a congenitally abnormal allantoic stalk/urachal remnant and a failure of embryological fusion of the dorsal bladder wall. Recovery was successful and the animal is now a healthy, 4-year-old western performance gelding. These specific congenital abnormalities have not been previously documented in the...
Pneumocephalus due to temporohyoid osteoarthropathy in a 16-year-old Friesian mare.
Journal of equine veterinary science    October 26, 2024   Volume 143 105210 doi: 10.1016/j.jevs.2024.105210
Witt P, Stas EKL, Hardeman LC, van Proosdij ER, Weerts EAWS, Lloyd-Edwards RA, Veraa S, Kranenburg LC, van den Boom R.A sixteen-year-old Friesian mare was admitted to the university clinic with the following clinical signs: anorexia, weight loss, fever, bilateral nasal discharge, unilateral facial paralysis and a non-healing corneal lesion. Endoscopic examination of the upper airways showed thickening of the proximal portion of the right stylohyoid bone. Computed tomography imaging showed pneumocephalus due to grade 3 unilateral temporohyoid osteoarthropathy (THO) with fracture of the petrous temporal bone. The horse did not improve following medical treatment. Surgical intervention was declined by the owner ...
Urinary incontinence and sabulous cystitis in mares: report of five cases.
Brazilian journal of veterinary medicine    October 21, 2024   Volume 46 e005024 doi: 10.29374/2527-2179.bjvm005024
de Melo UP, Ferreira C.This report describes five cases of urinary incontinence in Quarter Horse mares associated with the development of sabulous cystitis. The animals in this study had a history of persistent urinary incontinence for eight months, with clinical signs of continuous dribbling urine during rest and movement. The initial treatment with antibiotics and anti-inflammatory drugs was ineffective. Clinical examination revealed severe scalding in the perineal region and on the medial aspect of the hind limbs, along with neurological signs such as ataxia, hind limb paresis, and diminished perineal reflexes. T...
Lesion size index-guided radiofrequency catheter ablation using an impedance-based three-dimensional mapping system to treat sustained atrial tachycardia in a horse.
Equine veterinary journal    October 21, 2024   doi: 10.1111/evj.14424
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A, van Loon G.Sustained atrial tachycardia at an atrial rate of 191/min on the surface ECG was detected in a 6-year-old Warmblood mare. The vectorcardiogram obtained from a 12-lead ECG suggested a caudo-dorsal right atrial origin of the arrhythmia. Impedance-based three-dimensional electro-anatomical mapping, using the EnSite™ Precision Cardiac Mapping System revealed a clockwise macro-reentry around a line of conduction block in the caudomedial right atrium. Ten radiofrequency applications were applied to isolate the caudal vena cava myocardial sleeves at a power of 35 W and mean contact force of 14 ...
Third eyelid cartilage eversion in an adult mare.
Veterinary ophthalmology    October 11, 2024   doi: 10.1111/vop.13288
D'Agostino AL, Giuliano EA, Kuroki K, Martin LM.To describe the first report of third eyelid cartilage eversion in an adult American Quarter Horse mare. Methods: A 22-year-old American Quarter Horse mare presented to the University of Missouri Veterinary Health Center Equine Hospital for a 2-week history of a third eyelid cartilage abnormality of the left eye with no known recent trauma. Complete ophthalmic examination revealed third eyelid cartilage eversion of the left nictitans. The abnormal scrolled cartilage was surgically excised using a handheld cautery unit and submitted for histopathologic evaluation. Results: Histopathologic findi...
Concomitant melanoma and keratoma affecting the equine digit: clinical, pathological, and long-term follow-up findings.
BMC veterinary research    October 1, 2024   Volume 20, Issue 1 444 doi: 10.1186/s12917-024-04269-4
Bulnes F, Argüelles D, Buzón A, García-Álamo K, Rodríguez-Gómez IM, Hernández E, Mozos E.This case report details a long-term follow-up of a hoof melanoma with dermo-epidermal activity (resembling Spreading Superficial Melanoma (SSM)) in a bay horse with a history of a right front hoof keratoma. Melanomas involving the horse's foot are seldom reported and usually diagnosed as anaplastic melanomas based on signalment and post-mortem examination. The clinical-pathological characteristics of the foot melanoma in this bay horse are consistent with SSM-like described in humans, which is considered an intermediate malignant tumour attending their biological behaviour. However, a definit...
Grade IV gastric ulceration, pyloric aplasia, and an ectopic duodenal papilla in a 13-year-old Quarter Horse gelding evaluated for recurrent colic.
Journal of the American Veterinary Medical Association    September 25, 2024   Volume 262, Issue 12 1-5 doi: 10.2460/javma.24.05.0336
Barton CK, True A, Fenn M, Thampi P, Watson A, Smanik LE.The objective of this Case Report was to describe the clinical manifestation and postmortem findings of a horse evaluated for recurrent colic diagnosed with pyloric aplasia and an ectopic duodenal papilla. Methods: 13-year-old Quarter Horse gelding. Unassigned: The horse was presented to a referral center for signs of colic that were unresponsive to management on the farm. No abnormalities were noted on rectal palpation; however, upon passage of a nasogastric tube, 31 L of net gastric reflux was obtained. Gastroscopy noted grade IV squamous ulceration and moderate glandular ulceration, severe ...
Senecio ovatus poisoning in a horse – A case report.
Veterinarni medicina    September 22, 2024   Volume 69, Issue 9 329-336 doi: 10.17221/37/2024-VETMED
Kopecka A, Novotna T, Svobodova Z, Drabkova Z.This study describes a case of poisoning by pyrrolizidine alkaloids in a horse. To the best of the author's knowledge, this is the first confirmed case of Senecio ovatus poisoning. A six-year-old 450-kg Irish cob mare was presented to the Equine Clinic of the University of Veterinary Sciences Brno (Czechia) with symptoms of hepatic encephalopathy, which progressively worsened with time despite intensive therapy and led to euthanasia. A complex diagnostic and therapeutic approach including the post-mortem patoanatomical and histopathological examination is described here. Regar...
Closed laceration of the trachea, esophagus and guttural pouches in a mare caused by blunt trauma.
Journal of equine veterinary science    September 21, 2024   Volume 143 105196 doi: 10.1016/j.jevs.2024.105196
Lopes MAF, Hollenbach E, Schliewert EC, Murphy MA, Corrêa F.A mare was admitted for progressive swelling of the neck, lethargy and anorexia. Radiography revealed perilaryngeal, peritracheal, and periesophageal emphysema. Endoscopy revealed pharyngeal and tracheal roof collapse, and a small laceration on the trachea. Treatment with antimicrobials, fluids, and flunixin was initiated. To prevent exacerbation of the emphysema, temporary tracheostomy was performed. Clipping for the tracheostomy revealed a hoofprint mark on the ventral neck. Subsequent endoscopies revealed laceration of the esophagus and guttural pouch septum communicating with the visceral ...
Quadricuspid aortic valve in a 16-year-old Quarter horse.
Journal of equine veterinary science    September 20, 2024   Volume 142 105199 doi: 10.1016/j.jevs.2024.105199
Caivano D, Cicogna M, Orvieto S, Spitale D, Porciello F.A 16-year-old horse, 400 kg, male, Quarter horse gelding was examined for a cardiac murmur that had not been previously heard. Physical examination revealed a regularly irregular pulse and a grade III/VI, decrescendo, diastolic murmur with a point of maximum intensity over the left heart base. Base-apex standard electrocardiographic examination at rest showed sinus rhythm with second-degree atrio-ventricular blocks. Echocardiography identified the presence of four aortic valve cusps, two equal larger and two unequal smaller cusps. Color flow Doppler examination showed a diastolic regurgitant j...
Treatment of a urethral stricture by image-guided placement of a custom-made absorbable stent in a standing, sedated horse.
Journal of veterinary internal medicine    September 12, 2024   Volume 38, Issue 5 2795-2800 doi: 10.1111/jvim.17181
Baltrimaite M, Kearney C, O'Brien A, Duggan M, Cuq B.A 10-year-old Irish Sport Horse gelding developed complications from a general anesthesia resulting in sling support and recurrent urinary catheterization. The horse subsequently presented signs of dysuria and pollakiuria, was diagnosed with sabulous cystitis, and developed a urethral stricture from the repeated catheterizations, which was confirmed on urethroscopy. Clinical signs persisted despite conservative management with topical corticosteroids and urethral bougienage with balloon dilators. An image-guided approach was used to treat the stricture with a custom-made polydioxanone stent pl...
Association of Borrelia burgdorferi with nuchal bursitis and elevated outer surface protein A-specific serum antibodies in horses of the northeastern United States.
Journal of the American Veterinary Medical Association    September 6, 2024   1-9 doi: 10.2460/javma.24.05.0312
Pearson EK, Guarino C, Cercone M, Divers T, Lambert J, García-López J, Johnson AL, Engiles JB, Marconi R, Smith J, Brown K, Pinn-Woodcock T.Evaluate the incidence of Borrelia burgdorferi in cases of equine nuchal bursitis (NB) and investigate the relationship between elevated serum outer surface protein A (OspA) antibodies and the molecular identification of B burgdorferi in bursal tissue or synovial fluid. Additionally, describe clinical cases and compare the histologic changes in NB with and without detection of B burgdorferi. Methods: This was a retrospective multicenter cohort study (2013 to 2022). Medical records from horses with a diagnosis of NB and B burgdorferi PCR testing on NB tissue or synovial fluid were reviewed. The...