Abstract: Background: Baccharis coridifolia is one of the most important and common poisonous plants in Rio Grande do Sul (RS) state, Brazil (RS). The intoxication occurs when native livestock are exposed to the plant for the first time, especially when they are hungry, thirsty and stressed after transportation. The lesions associated with the toxicosis are characterized necrosis of the epithelial lining of the pre-stomachs. Cases of intoxication by Baccharis spp. in sheep native of a certain farm are uncommon. The objective of this study is to report an outbreak of B. coridifolia poisoning in lambs in RS, Southern Brazil, and to address the epidemiological, clinical and pathological aspects of this condition. Cases: Ten 15-20 day-old Corriedale and Texel lambs from a lot of 150 were affected. The onset of clinical signs occurred two days after the lambs were moved from ryegrass (Lolium multiflorum) pasture to a native pasture with moderate amounts of sprouting B. coridifolia. Main clinical signs were intense abdominal pain, during which some lambs distended the thoracic and pelvic limbs while standing up, diarrhea, dehydration, ruminal atony, salivation, decubitus and death. Gross lesions in three necropsied lambs were mainly located in the digestive tract and included varying degrees of hyperemia, edema and erosions in the fore stomach mucosae. Histologically, there were hyperemia and degenerative, necrotic and ulcerative changes in the epithelial lining of forestomachs. The lesions observed were characterized by hydropic degeneration stratified mucosal epithelium and multifocal intercellular edema. Necrosis of individual epithelial cells, which had the intensely eosinophilic cytoplasm with a pyknotic or karyorrhetic nucleus, was observed. Multiple clefts were seen at the junction of the epithelium with the lamina propria, some of which containing intact and viable neutrophils. In addition, one of the sheep demonstrated focal extensive areas of moderate proliferation of granulation tissue in the submucosa of the forestomachs. Discussion: The diagnosis of B. coridifolia intoxication was based on the anatomopathological findings and on the presence of the plant in the pasture where the lambs were held. The lack of other plants, such as other species of Baccharis, Eupatorium tremulum and Baccharidastrum triplinervium, capable of producing a similar disease, reinforces the definitive diagnosis. Differently, from what is reported in the literature, the outbreak of B. coridifolia intoxication in this study occurred in lambs born on the farm. The toxicosis affected 15-20-day-old lambs, the age group in which lambs developing grazing habits. Similar to what occurred in an outbreak of B. megapotamica intoxication in lambs, it is probable that the lack of previous knowledge of the plant by the lambs was the main predisposing factor of the outbreak reported here. This is suggested by the involvement of only lambs and not adult sheep, the latter of course not native in relation to the plant. Affected lambs developed an acute clinical course with digestive signs. Deaths are usually related to pre-stomach injuries caused by the toxic action of macrocyclic trichothecenes, associated with dehydration and diarrhea, resulting in an electrolyte imbalance. Intoxication by B. coridifolia should be considered a differential diagnosis in lamb mortalities, mainly during the development of grazing habit. In order to avoid the occurrence of Baccharis coridifolia intoxication in sheep, it is recommended the previous adaptation with a gradual introduction of the sheep under close observation. [ABSTRACT FROM AUTHOR]
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