Central Blindness Associated with a Pituitary Adenoma in a Mare

Background: Pituitary pars intermedia (PI) adenoma is a benign adenohypophysis neoplasm, rare in Brazil, which may compress adjacent structures and lead to dysfunctions of the endocrine organs. The most affected species are equines, particularly aged animals. This neoplastic disease is often associated with Cushing's syndrome, when the pituitary-adrenocortical axis is affected. However, this neoplasm is seldom associated with clinical blindness. This paper describes a case of pituitary pars intermedia (PI) adenoma which caused blindness in a mare.Case: An emaciated, blind mare that had difficulty finding water and food was referred to “Hospital Veterinário de Grandes Animais” of “Universidade Federal Rural do Rio de Janeiro”, in Seropédica, state of Rio de Janeiro, Brazil, and later to the “Setor de Anatomia Patológica” (SAP/UFRRJ) for necropsy. During necropsy it was found that the animal’s pituitary gland consisted of a circumscribed globous mass measuring 3.5x2.5x2.5 cm, symmetrical and well delimited at the sella turcica. Several organs were collected, fixed in 10% formalin and then processed for histological examination. The brain was subjected to serial cleavage along the path of the vision organs. All collected tissues were stained with hematoxylin and eosin; the pituitary was stained with Schiff Periodic Acid (PAS) to differentiate neoplastic cells and with Luxol Fast Blue to evidence demyelination. Histopathology found that the pars intermedia (PI) was thickened and compressed the neurohypophysis and adenohypophysis. Cells were arranged in a disorganized manner or formed follicles or cysts containing eosinophilic material (colloid), with granules strongly positive after staining with PAS. Proliferated cells were large, polyhedral to ovoid, and contained clear basophilic granular material. The nuclei were spherical to ovoid and there were light anisocytosis and anisocariasis. Cysts were frequently found in the pars intermedia (PI) and occasionally in the pars distalis. Mitoses were rare, less than one per field of greatest increase. In some areas of the pars intermedia (PI), cells were arranged in a solid manner forming spherical sub-nodules. An orange yellow pigment was observed in the pericary (lipofuscinosis) in various neurons of several areas of the central nervous system and of the trigeminal ganglion. In the optic tract, there were areas with moderate demyelination, evidenced by Luxol Fast Blue staining, and macrophages characterizing the so-called digestion chambers. In the right and left lateral geniculate nuclei a focal area of neurons with pyknotic and peripheral nuclei, marginal Nissl substance (central chromatolysis) and atypical and reactive astrocytes was observed, with increased volume, evident cytoplasm and nuclei with marginated chromatin which was sometimes reniform.Discussion: This paper presents the pathological findings obtained from a mare with central blindness due to pituitary pars intermedia adenoma. The analysis of the structures affected and correlation of alterations with the respective clinical signs are compared with alterations in other areas of the pituitary which generate clinical signals not observed in this mare, but which occur more often in equines with tumors in that organ. Thus, central and bilateral blindness was associated with compression of the optical tracts by the neoplastic mass and consequent death of neurons of the lateral geniculate nucleus. Pituitary PI adenoma should be considered as a differential diagnosis for blindness

Emphysematous and Granulomatous Submucosal Rumenitis in a Feedlot Nellore Steer.

Background: Emphysematous rumenitis is a condition characterized by gas filled bubbles or cysts in the ruminal mucosa. Although a similar pathology is reported from swine and humans, the incidence of this disease in cattle seems to be scarce. The etiology of emphysematous rumenitis is uncertain once many factors can be involved in its pathogeny, a single cause is difficult to ascertain. This lesion usually fails to display specific clinical signs; however, some degree of malabsorption and weight loss is expected. We described a case of emphysematous granulomatous submucosal rumenitis in a 2.5-yearold feedlot Nellore steer that presented reduction on daily weight gain.Case: Rumen fragments of a 2.5-year-old Nellore steer were submitted for histopathological evaluation at the Sector of Pathological Anatomy (SAP) of the Rural Federal University of Rio de Janeiro, Brazil. The specimens were part of an experimental trial to evaluate the effect of phosphorus (P) supplementation on nutrient intake, performance and P balance in fifty feedlot Nellore steers. Following a short adaptation period, in which behavioral observations were made twice daily to assess possible adverse factors, all steers were fed with balanced diet for one hundred and sixteen days. The steers were then slaughtered in order to evaluate macroscopic changes in the gastrointestinal system. Rumen and abomasum of each steer was emptied, washed with tap water and grossly examined. One steer presented ruminal lesion, while the other forty-nine did not show any ruminal injury. Throughout the experiment the affected steer showed reduction of daily weight gain; but during clinical examination no additional clinical sign was seen. At gross inspection, a reduction in the amount of muscular and adipose tissue was seen. Multiple coalescent bullous elevated structures measuring three to ten mm diameter were covering about 40% of the ruminal surface. The affected ruminal mucosa showed irregular and atrophic papillae. Rumen samples were processed routinely and stained with Hematoxylin and Eosin, Period Acid Schiff (PAS), Grocott’s Methenamine Silver (GMS), Ziehl-Neelsen (ZN), Brown-Hopps (Gram), Giemsa and Toluidine Blue (TB) stains. Additionally formalin-fixed, paraffin wax-embedded sections were stained with a primary polyclonal rabbit antibody for Escherichia coli. Histologically the submucosa was largely replaced by cyst-like enlarged lymphatic vessels filled with gaseous content and the ruminal submucosa was infiltrated by macrophages, multinucleated giant cells, eosinophils, lymphocytes and plasma cells. Special stains were negative for granules within the mast cells, fungi, acid-fast bacilli, bacteria and protozoa. E. coli was immuno-labeled only at the ruminal epithelial surface.Discussion: This paper provided a description of a rare and possible underdiagnosed condition in cattle to highlight the necessity of recognizing ruminal changes during slaughterhouse inspection. The spontaneous and extensive emphysematous rumenitis described in this paper showed histological similarities with the analogous condition documented in the small and large intestine, mesentery and mesenteric lymph node of swine. The etiology and pathogenesis of emphysematous submucosal rumenitis remain unknown. We believe that the lesion described was the reason for the decrease of weight gain of the steer; therefore it should be considered as a differential diagnosis for conditions that affect weight gain and performance of cattle.Keywords: cattle, veterinary pathology, feedlot, emphysema, rumen

Infiltração de leucócitos e imunorreatividade antimieloperoxidase em granulócitos da mucosa e submucosa do intestino grosso de equinos submetidos à sobrecarga dietética com amido

Este estudo teve como objetivo avaliar a infiltração de leucócitos e a imunorreatividade antimieloperoxidase em granulócitos da mucosa e submucosa do intestino grosso de equinos submetidos à sobrecarga dietética com amido. Oito equinos adultos foram distribuídos aleatoriamente em três tratamentos: Tratamento I (Controle) (n = 2), equinos eutanasiados sem sobrecarga com amido; Tratamento II (n = 3) e III (n = 3), equinos submetidos à sobrecarga com amido, com infusão gástrica de 17,6 g de amido/kg de peso vivo e eutanasiados após 24 e 36 horas, respectivamente. Observou-se apenas afluxo de neutrófilos (leucocitoestase) nos vasos sanguíneos da mucosa e submucosa intestinal. Eosinófilos foram as células predominantes na mucosa e submucosa em todos os equinos, independente da sobrecarga dietética, com grau de infiltração de leve a moderada. Infiltração por linfócitos também foi observado em todos os equinos, porém com menor intensidade quando comparado aos eosinófilos. Congestão, edema e dilatação de vasos linfáticos foram as principais alterações circulatórias observadas, com maior intensidade na submucosa. Maior imunorreatividade para anticorpos antimieloperoxidase foi observado na mucosa e submucosa dos equinos 36 horas após a sobrecarga. Equinos submetidos à sobrecarga dietética com amido apresentam resposta inflamatória intestinal com predominância de eosinófilos, leucocitoestase e alterações circulatórias variando de discreta a moderada.This study was carried out to evaluate leukocyte infiltration and anti-myeloperoxidase immunoreactivity in granulocytes of the mucosa and submucosa of the large intestine of horses submitted to dietetic starch overload. Eight adult horses were allocated randomly in three treatments: Treatment I (Control) (n = 2), animals euthanized without starch overload; and Treatments II (n = 3) and III (n = 3), animals undergoing starch overload, with gastric infusion of 17.6 g starch per kg of body weight, euthanized after 24 and 36 hours, respectively. Only afflux of neutrophils in the intestinal mucosa and submucosa blood vessels (leukocyte stasis) was observed. Eosinophils were the predominant cells in the mucosa and submucosa in all horses, independent of dietetic overload, with infiltration grade from mild to moderate. Lymphocyte infiltration was also observed in all horses, but with lower intensity when compared to eosinophils. Congestion, edema and dilatation of lymphatic vessels were the main circulatory alterations observed, with more intensity in the submucosa. Higher immunoreactivity to the anti-myeloperoxidase antibodies was observed in the mucosa and submucosa of horses 36 hours after overload. Horses submitted to dietetic starch overload showed intestinal inflammatory response with prevalence of eosinophils, leukocyte stasis and circulatory alterations, varying from discreet to moderate

Lasalocid Poisoning in Buffalo Calves in the State of Pará, Brazil

Background: Ionophore antibiotics are food additives with coccidiostatic or antimicrobial action; they are also used as growth promoters, ruminal pH regulators, volatile fatty acid molar modifiers, and methanogenesis reducers. However, these compounds have the potential to cause microbial resistance, in addition to the risk of intoxication. Ionophore poisoning may be caused by excessive intake, sensitivity of certain animal species, and concomitant use with other drugs. In Brazil, cases of ionophore poisoning in buffalos are rare. This study aims to describe the epidemiological, clinical, and pathological findings of lasalocid poisoning in buffalo calves.Case: A visit was made to a farm in the municipality of Mojú, Pará state to care for Murrah buffalo calves. After weaning, the buffalos were grazed in paddocks with Panicum spp., and received a supplement of mineral, protein, and vitamin. This supplement contained, per kg, 250 g PB, 50 g Ca, 20 g P, 8 g S, 39 g Na, 20 mg Co, 557 mg Cu, 200 mg Fe, 12.4 mg Se, 2040 mg Zn, 0.19 mg biotin, 26750 IU of vitamin A, 4175 IU of vitamin D, 155 IU of vitamin E and 300 mg/kg of lasalocid. The product was made available to all calves, at 1-2 g/kg body weight (BW), according to the manufacturer's recommendations. Older calves were raised together with those less than 30 days old; as a result, the older calves tended to eat more, which could lead to a supplementation consumption of more than 1 kg body weight per animal per day. It was reported that between 40 and 60 days after the introduction of this supplement, 16 calves fell ill and died due to apathy, motor instability, tremors, and distended neck. The herd had a mortality rate of 33.3%. Two calves underwent a necroscopic examination at the Pathology Section of the Veterinary Institute of the Federal University of Pará. Macroscopic examination revealed extensive pale areas in the skeletal muscles, myocardium, and tongue. Fragments of these muscles and various organs were collected, fixed in 10% buffered formalin, processed according to the routine histological technique, and stained with hematoxylin-eosin and Masson's trichrome stain. Microscopic examination of the histologic samples revealed foci of muscle atrophy and necrosis characterized by an increase in cytoplasmic eosinophilia associated with the loss of stretch marks, and hyperchromatic nuclei that were displaced to the periphery. The necrosis of the muscle fibers was highlighted by Masson's trichrome staining.Discussion: The diagnosis of lasalocid poisoning in buffalo calves was based on epidemiological data, clinical findings, results of macroscopic and histopathological examination, and based on the estimated ionophore intake, obtained directly from the supplement label and by the calf's handler. Based on the absence of stratification of the calves by similarity of age and because the buffalo calves older than 30 days could eat more than 1 kg of the supplement (containing 300 mg/kg of lasalocid), it was possible to estimate the intake of lasalocid per kg CP (body weight). Therefore, the intake of lasalocid by a 70-kg buffalo calf in approximately 90 days and daily supplement consumption between 1 and 1.5 kg would be between 4.2 and 6.4 mg/kg of body weight. This report reinforces that notion that buffalo calves should never ingest ionophores; however, if necessary, strict protocols must be followed to avoid poisoning in these animals. This study highlighted the fact that stratification of buffaloes by different age groups during feeding became a risk factor that allowed greater consumption by older animals; this led to the estimated consumption of 4.2-6.4 mg/kg of lasalocid.Keywords: ionophores, ruminants, buffalo calves, muscle necrosis.Descritores: ionóforos, ruminantes, bezerros búfalos, necrose muscular.Título:  Intoxicação por lasalocida em bezerros búfalos no Estado do Pará, Brasil 

Hemorrhagic Meningoencephalomyelitis Due to Ectopic Localization of Aelurostrongylus abstrusus in a Cat: First Case Report

The lungworm Aelurostrongylus abstrusus is one of the main causes of respiratory diseases in cats worldwide. This report describes the unusual case of a kitten infected with A. abstrusus and presented to a veterinary clinic in Brazil with lethargy, dysphagia, non-ambulatory tetraplegia, and pelvic limbs bilateral myoclonus. The clinical picture of the kitten worsened with generalized flaccid tetraplegia and death a few days after hospitalization. At necropsy, hemorrhagic necrosis and subarachnoid hemorrhages were detected in several areas of the central nervous system. Nematode stages were found at post-mortem histological examinations in lungs, cerebellum, subarachnoid space of the brain and spinal cord. Microscopic and molecular (PCRs-coupled-sequencing protocols) examination showed the presence of A. abstrusus in histological samples. This study describes the first neurological aelurostrongylosis due to ectopic localization of adult worms in the central nervous system of a cat, causing acute hemorrhagic multifocal meningoencephalomyelitis. Further studies are necessary to elucidate whether unusual localizations and the migration of A. abstrusus are more frequent than expected

Jürgen Döbereiner : uma vida dedicada à ciência

Dr. Jürgen Döbereiner was born in Germany, on the 1st of November 1923, and lived in Brazil for 68 years during which time he developed a range of scientific projects in veterinary pathology and related disciplines. His main interests were the identification of new poisonous plants and mineral deficiencies and the causes of “cara inchada” (“swollen face” a periodontal disease) and botulism in livestock. This research has resulted in the improved health and saving of hundreds of thousands of animals, mainly cattle, annually, and is consequently of enormous economic value to the country. This contribution remains largely under appreciated. He was also involved in organizing diagnostic methods for identifying infectious diseases such as African swine fever and glanders in horses. One of his other major achievements has been the foundation and editing of specialized scientific journals for the documentation of veterinary science research results. At the beginning of his career in the 1950s, he and colleagues from the Institute for Animal Biology (IBA) were struggling to find a national scientific journal where research results from veterinary medicine could be published with practical application to the Brazilian reality. In consequence, the team founded “Arquivos do Instituto de Biologia Animal” and published three volumes (1959-1961). He then founded and edited “Pesquisa Agropecuária Brasileira” (The Brazilian Journal of Agricultural Research”) that included a veterinary section. A series of veterinary volumes were published (1966-1976). Finally, in 1978 he helped create the Brazilian College of Veterinary Pathology (CBPA) that published “Pesquisa Veterinária Brasileira” (The Brazilian Journal of Veterinary Research) from 1981. The main goal was to communicate the most relevant disease problems of Brazilian livestock, in particular pathology and related subjects such as epidemiology, clinical study series and laboratory diagnosis to field veterinarians and academics. Dr. Jürgen Döbereiner was president of CBPA (1978-2018) and chief editor of “Pesquisa Veterinária Brasileira” (1981-2018). He passed away on the 16th of October, 2018, at the age of 94 at his home in Seropédica/RJ, Brazil.Dr. Jürgen Döbereiner nasceu na Alemanha em 1 de novembro de 1923, durante 68 anos viveu no Brasil e desenvolveu trabalhos científicos no campo da patologia veterinária latu sensu. Sua contribuição científica de destaque foi em temas como plantas tóxicas de interesse pecuário, deficiências minerais em animais de produção, cara inchada (doença periodontal) dos ruminantes, botulismo e diagnóstico de doenças infecciosas. Estas pesquisas resultaram na melhoria da saúde e de centenas de milhares de animais, principalmente bovinos e, consequentemente, foram de enorme valor econômico para o país. Esta contribuição ainda permanece em grande parte subestimada. De grande destaque para a ciência brasileira foi ainda a sua atuação profissional na documentação científica de resultados de pesquisa. No início de sua carreira na década de 1950, Dr. Döbereiner e outros pesquisadores do Instituto de Biologia Animal (IBA) detectaram a necessidade de um periódico científico nacional para publicar resultados de pesquisas com aplicação pratica à realidade brasileira. Dessa iniciativa surgiram os Arquivos do Instituto de Biologia Animal, que publicou três fascículos (1959-1961), em seguida o Dr. Jürgen Döbereiner participou na fundação da revista Pesquisa Agropecuária Brasileira que publicou a Série Veterinária (1966-1976) e finalmente em 1978, houve a fundação do Colégio Brasileiro de Patologia Animal (CBPA) que publica desde 1981 a revista Pesquisa Veterinária Brasileira. Este periódico científico foi criado para apresentar à comunidade, principalmente veterinários de campo e professores, os principais problemas de saúde em animais de produção no Brasil, ou seja, patologia em seu sentido amplo, envolvendo as áreas de epidemiologia, clínica e diagnóstico laboratorial. Dr. Jürgen Döbereiner, que foi presidente do CBPA (1978-2018) e Editor-Chefe da revista Pesquisa Veterinária Brasileira (1981-2018), faleceu em casa, em 16 de outubro de 2018, aos 94 anos, no município de Seropédica/RJ

Angiolipoma in a Dog

Background: Angiolipoma is a benign tumor composed of endothelial cells and mature adipocytes. Tumors reported in domestic species include two variants; infiltrative or non-infiltrative. Bitches and intact males seem predisposed. This mesenchyme tumor is commonly mistaken with lipoma due to its soft texture and subcutaneous site and often requires histopathology to confirm its diagnosis. Microscopic examination also enables the evaluation of surgical margins and rule out possible infiltrative sites. Complete surgical excision is usually curative. This study reports a case of non-infiltrating angiolipoma in a dog.Case: A 14-year-old mixed-breed dog was presented to a veterinary clinic in the city of Rio de Janeiro, RJ, Brazil. On palpation, a painless mass was noted, with high mobility and covered by intact hirsute skin in the right subcutaneous ventrolateral region. Computed tomography of the chest showed an expansive mass of uptake only from the edges of the soft tissues of the right subcutaneous ventrolateral region. The mass was homogeneous and well delimited, suggesting a neoplastic process. Subsequently, the mass was surgically removed, fixed in 10% buffered formalin, and sent for histopathological analysis. On macroscopic examination, the mass was well delimited, without skin coverage, and measured 2.3 × 1.9 × 0.6 cm. The consistency was smooth and unctuous in appearance with a compact cream-colored surface with blackish multifocal spots. Under microscopy, the histological sections showed neoplasm of mature adipocytes and of endothelial cells of blood vessels benign were filled with a marked amount of red blood cells. Multifocal fibrin thrombi and a mild inflammatory infiltrate composed of lymphocytes and rare mast cells were evident. There was no infiltration in the regional skeletal musculature. Thus, a diagnosis of non-infiltrative angiolipoma was established.Discussion: The diagnosis of non-infiltrating angiolipoma in this case was established through the results of histopathological examination. The occurrence of this neoplasm in dogs is uncommon, and the data reported in the veterinary medicine literature are scarce. However, in this study, it was found that the neoplasm on screening presented a behavior like that of lipomas, with noninvasive growth and the absence of local recurrence. The canine species does not commonly convey pain on palpation during a clinical examination, as observed in the present case. In humans, multiple angiolipoma nodules are common; this clinical presentation differs from that in animals, in which solitary nodules are generally observed. In dogs, as in the present case, they seem to have a predilection for the trunk. In animals, the pathogenesis of angiolipomas is not established, but in humans, it is based on theories that include the reaction to harmful stimuli and congenital malformation of adipose tissue. In humans, the presence of fibrin thrombi on the periphery of the region of cell proliferation are microscopic findings that can assist in the diagnosis of angiolipomas, an approach that was implemented in the present case. The occurrence of this neoplasm in dogs is uncommon, and the data reported in the veterinary medicine literature are scarce. The importance of an adequate description of angiolipomas is based on the need to provide information about its epidemiology, biological behavior, and prognosis

Metastatic Hemangiosarcoma in a Cow

Background: Hemangiosarcoma is a malignant mesenchymal neoplasm of endothelial cells that mainly affects dogs and is less common in horses, cattle, goats, pigs, and sheep. In ruminants, however, few cases of hemangiosarcoma have been reported. Although this neoplasm may primarily occur in any tissue, it most often originates in the spleen, liver, heart, and skin. This study reports the clinical and pathological findings of a bovine hemangiosarcoma.Case: A 10-year-old lactating Girolando cow from the municipality of Vassouras/RJ was examinated because of uncontrolled cough and bilateral hemoptysis, loss of appetite, fever, weight loss, severe decline in milk production (a decrease of 28 L), and respiratory wheezing during chest auscultation. We performed a necropsy and collected fragments of various organs which were fixed using 10% buffered formalin and sent to the Pathology Anatomy Sector (SAP) of the Federal Rural University of Rio de Janeiro (UFRRJ) for routine histological assessment. Macroscopically, large hemorrhagic areas were observed in the lungs, mainly in the cranioventral portion of the pulmonary lobes, multifocal areas of hemorrhages in the liver, and a 10x8x5 cm soft red mass was observed in the spleen. Microscopically, was observed lung proliferation of endothelial cellsarranged in tapes, supported by a collagenous stroma associated with severe multifocal lobular hemorrhage with a large number of siderophages and diffuse and marked edema, and congestion. In the mediastinal lymph node, liver, and spleen, the proliferation of neoplastic endothelial cells equivalent to those described in the lungs was observed. The histologicalsections of liver and tumor spleen were subjected to immunohistochemical analysis for von Willebrand factor, in which marking was observed in neoplastic endothelial cells.Discussion: Previously, neoplasms in Brazilian cattle have been presented as case reports or, more recently, as scarce retrospective studies, signifying that hemangiosarcoma is a rare neoplasm in the bovine species. Among several studies, we highlight the one conducted in Rio Grande do Sul with neoplastic lesions found in bovine slaughterhouses, in which onlyone case of hemangiosarcoma was observed in 1.5% (1 of 65) cattle. In addition, similarities were also noted in a study of neoplastic lesions in bovine slaughterhouses in Canada, in which hemangiosarcoma was diagnosed in 0.3% (4 of 1370) cattle. In the present study, the positive immunostaining of neoplastic endothelial cells was easily identified from von Willebrand factor, also called factor VIII, and is similar to other studies described in the literature. In a serie of twelve cases of vascular tumors in domestic animals (dogs, horses and cattle), 100% were positive for von Willebrand factor and served to distinguish tumors of epithelial or histiocytic origin. Although the clinical signs observed in our case are non-specific, hemoptysis was the most intense signal and the only clinical manifestation that may indicate an important pulmonary lesionthat indicated possible pulmonary neoplasm. Among other diseases, the acute form of Pteridium aquilinum poisoning, thrombocytopenia, anticoagulant rodenticide toxicity and vena cava syndrome might cause hemoptysis, and therefore, should be incorporated in the list of differential diagnoses of neoplasm that occur with pulmonary metastasis. Further, neoplastic and or hemorrhagic diseases affecting cattle should be differentiated of hemangiosarcoma.Keywords: hemangiosarcoma, diseases of cattle, neoplasia

Ruptura Bilateral do Músculo Fibular Terceiro em Bovino

Background: The peroneus tertius muscle is responsible for tarsal flexion and coordinate extension of the stifle joint. The most common causes of rupture are excessive effort when trying to rise on a slippery surface, mounting, or being mounted. Rupture of the peroneus tertius muscle is characterized by an inability to flex the hock. Most cases are not curable, presenting an unfavorable to poor prognosis, and the animal has to be euthanized. This study aimed to report the clinical picture and treatment of a bilateral rupture of the peroneus tertius muscle in a cow from the municipality of Castanhal, state of Pará (Amazonian biome). Case: We report the clinical picture and treatment of a bilateral rupture of the peroneus tertius muscle in a 4-year-old cow, mixed breed, weighing approximately 400 kg, calved 3 months ago, belonging to a batch of 40 cattle kept on extensive breeding system in a pasture of Urochloa (Brachiaria) brizantha. The clinical signs appeared after the cow was mounted by a 1,100 kg bull and consisted of lameness, falling into sternal decubitus with hind limbs extended backward, hyperextension of the hocks with flexed stifle, with the tibia and metatarsus in a straight line, which lead to a 90-degree position of the femur and knee. Abrasions in the dorsal region of the fetlocks reinforce evidence of dragging hooves. Diagnosis of bilateral rupture of the peroneus tertius muscle was performed by a clinical examination and semiological test. Non-steroidal anti-inflammatory drugs (flunixin meglumine, 2,2 mg/kg, every 24 h for 4 days) were prescribed for treatment, in addition to resting in a paddock with good availability of pasture, water, and mineral salt. After 3 months, we observed an improvement of the clinical signs, and after 6 months, an almost complete recovery. Only a slight difficulty in flexing the hock when moving remained. Discussion: In the present report, bull mounting was the probable cause of the hyperextension of both hocks and the bilateral rupture of the peroneus tertius muscle. According to the handler, these clinical signs were only evidenced after the animal was mounted. As stated in the literature, accidents such as falls, slips, mounting or being mounted, as well as excessive traction and over-elevation of the limb are considered predisposing factors for the onset of the disease. Rupture of the peroneus tertius muscle is unusual in production animals; therefore, the low occurrence of reports on this kind of rupture in the literature makes this case even more unique. The bilateral injury differs from cases described in the literature, in which the reported injuries were always unilateral. Our findings reinforce the hypothesis that the act of mounting was the triggering factor for the bilateral rupture of the animal peroneus tertius muscle. The breeding system also differs from the cases diagnosed by the same authors, since they describe the disease in bovines kept on intensive or semi-intensive breeding. In the present case, the cattle were kept on an extensive breeding system. The extension and flexion tests used in the clinical examination allowed for the diagnosis of rupture of the peroneus tertius muscle in both limbs, similarly to what has been reported by other authors. Anamnesis, clinical findings, and exclusion of different diagnoses were decisive for establishing the diagnosis. The treatment chosen was efficient, even though the case was severe, as the injury occurred in both hind limbs. Keywords: cattle disease, muscle injury, lameness, rupture. Título: Ruptura bilateral do músculo fibular terceiro em bovino Descritores: doença do gado, lesão muscular, claudicação, ruptura.Background: O músculo fibular terceiro é responsável pela flexão do tarso e extensão coordenada da articulação fêmuro-tíbio-patelar. As causas mais comuns da ruptura são o esforço excessivo ao se levantar em piso escorregadio, montar ou ser montado por outros animais, entre outras causas. A ruptura do músculo fibular terceiro é caracterizada pela incapacidade de flexão do jarrete e, na maioria dos casos, não há recuperação, o prognóstico geralmente é desfavorável a ruim e o animal é destinado à eutanásia. O objetivo deste estudo foi relatar o quadro clínico e o tratamento empregado na ruptura bilateral do músculo fibular terceiro em uma vaca do município de Castanhal, estado do Pará (bioma amazônico). Case: Descreve-se o quadro clínico e o tratamento empregado na ruptura bilateral do músculo fibular terceiro em uma vaca, com quatro anos de idade, sem raça definida, com aproximadamente 400kg, parida há três meses, pertencente a um lote de 40 bovinos mantidos em sistema de criação extensiva em pastagem de Urochloa (Brachiaria) brizantha. Os sinais clínicos surgiram após ser coberta por um touro de 1.100Kg e consistiram em claudicação, queda em decúbito esternal com os membros posteriores estendidos para trás, hiperextensão dos jarretes com a soldra flexionada, ficando a tíbia e o metatarso em linha reta, levando a formação de um ângulo de 90º entre o fêmur e o joelho. As escoriações na região dorsal dos boletos pélvicos reforçam a evidência do arrastar das pinças. O diagnóstico da ruptura bilateral do músculo fibular terceiro foi realizado por meio do exame clínico semiológico. No tratamento foi prescrito anti-inflamatório não-esteroidal (flunixin meglumine, 2,2 mg/kg, a cada 24h, durante quatro dias) e repouso em um piquete com boa disponibilidade de pastagem, água e sal mineral. Após três meses observou-se a melhora dos sinais clínicos e após seis meses uma recuperação quase completa, permanecendo apenas uma leve dificuldade de flexionar o jarrete no momento da locomoção. Discussion: No presente relato, a monta do touro foi a provável causa da hiperextensão de ambos os jarretes e a ruptura bilateral dos músculos fibulares terceiros. A lesão bilateral difere de casos descritos em livros e artigos em que as lesões relatadas foram sempre unilaterais, reforçando a hipótese de o ato da monta ter sido o fator desencadeante da ruptura bilateral do músculo fibular terceiro do animal. Conclui-se que a anamnese, achados clínicos e exclusão de diagnósticos direfencias foram decisivos para instituição do diagnóstico. O tratamento instituído foi eficiente, mesmo se tratando de um caso grave, no qual a lesão ocorreu em ambos os membros posteriores