Severe urticaria in a horse after consumption of horseweed (Conyza canadensis (L.) Cronquist) - A case study.

Our paper presents a case study of a Welsh pony mare with grazing-induced severe urticaria. The main clinical signs were eye swelling, depression and extensive urticaria. Physical examination revealed no other abnormalities. Botanical sampling revealed horseweed (Conyza canadensis) as the most abundant species and a potential allergen plant due to sesquiterpene lactones (SQL). Differential diagnosis strongly suggested that the clinical signs were the result of a hypersensitivity reaction to this plant. Former studies brought controversial data about the toxic or allergic potential of horseweed especially for equids thus our paper is the first interpretation of horseweed induced urticaria.