Background:Cyathostomosis is the infection by nematode larvae of small strongyles belonging to the subfamily Cyathostominae (cyathostome). It is primarily a disease of young horses with global distribution. The parasites cause severe injuries to the intestine and the clinically affected animals have severe diarrhea, colic, intussusception, and less frequently intestinal infarction. The aim of this study is to describe the pathological findings of enteritis by cyathostome on a donkey in Brazil. Case:A donkey (Equus asinus), crossbred female mongrel, approximately four-months-old, was referred to the Veterinary Hospital of the Federal University of Campina Grande, Patos, PB, Brazil with a history of trauma. On clinical examination, complete fracture of the left femur was identified. After performing euthanasia the donkey was necropsied. The animal was skinny with pale mucous membranes. The perineal region, base of the tail and hind limbs were dirty with yellowish fecal content. At necropsy, the large intestine had a pasty content and the mucosa was thickened with the multifocal whitish or dark red nodules. The cut surface of these nodules showed caseous material, sometimes associated with larvae in the submucosa. Microscopically, it was observed granulomatous and eosinophilic chronic multifocal associated with intralesional larvae of cyathostome-like nematodes. In the mucosa and submucosa of the colon and cecum, there were multifocal to coalescing granulomas composed by moderate inflammatory infiltrate composed of eosinophils, macrophages, epithelioid cells, neutrophils and occasional multinucleated giant cells, surrounded by fibrous tissue and infiltrated by lymphocytes and plasma cells. At the center of these granulomas transverse and longitudinal sections of nematode larvae with approximately 160-550?m in diameter were observed within the necrotic material. The parasites presented a smooth, thick and eosinophilic outer cuticle, clear platymyarian muscles, internal cuticular crests, vacuolated lateral strings, and intestine composed of multinucleated cells in the large colon and caecum. There were no mature gonads, featuring the larval stage. Discussion:Parasitic infections are the most common diseases that threaten donkey health and performance. In this species, small strongyles infections are severe, since the larvae can infiltrate and form cysts in the wall of the large intestine causing serious damage. The most common clinical signs caused by cyathostome are weight loss and diarrhea, which are non-specific and consequently can lead to an underestimation of the disease occurrence. In this case, massive infection of small strongyles was observed in the large colon and caecum. In contrast to the large strongyles, the small strongyles do not migrate through tissue but severely injure the large intestine of donkeys, zebras and horses. Other possible causes of enteritis in horses include Salmonella spp., Rhodococcus equi, Clostridium perfringens, Clostridium difficile, Neorickettsia (Ehrlichia) ristcii infections, and idiopathic and neoplastic conditions (lymphoma). In the present report, the diagnosis of larval ciatostomose was based on clinical signs, and especially in the severity of pathological findings associated with morphological characteristics of the larvae of nematodes compatible with cyathostome in the large intestine.