Xanthium strumarium, commonly referred to as “cocklebur,” rarely causes poisoning in cattle. When mature, this
robust, annual weed bears numerous oval, brownish, spiny burs. Only the seeds in the burs and young seedlings (cotyledonary
leaves) contain the toxic principle, carboxyatractyloside. In the Frankfort district of the Free State Province of South Africa,
a herd of 150 Bonsmara cows were allowed to graze on the banks of a small river, where mature cocklebur was growing.
Four cows died while grazing in this relatively small area. Clinical signs ranged from recumbency, apparent blindness, and
hypersensitivity to convulsive seizures. During necropsy, burs completely matted with ingesta were located in the rumen
content. The most distinctive microscopic lesions were severe, bridging centrilobular to midzonal hepatocyte necrosis and
hemorrhage. Ultrastructurally, periacinar hepatocytes were necrotic, and novel electron-dense cytoplasmic needle-like crystals
were observed, often in close association with peroxisomes. Carboxyatractyloside concentrations were determined using liquid
chromatography–high-resolution mass spectrometry (LC-HRMS). Carboxyatractyloside was present in rumen contents at 2.5
mg/kg; in burs removed from the rumen at 0.17 mg/kg; in liver at 66 ng/g, and was below the limit of quantitation in the kidney
sample, estimated at approximately 0.8 ng/g. Based on the presence of the plants on the riverbank, the history of exposure, the
clinical findings, the presence of burs in the rumen, and the microscopic and ultrastructural lesions, X. strumarium poisoning
in the herd of cattle was confirmed and was supported by LC-HRMS.