Experimental rayless goldenrod (Isocoma pluriflora) toxicosis in goats.

Rayless goldenrod (Isocoma pluriflora) sporadically poisons livestock in the southwestern United States. Similarities with white snakeroot (Ageratina altissima) poisoning and nearly identical chemical analyses led early researchers to conclude that tremetol, a mixture of benzofuran ketones, is the rayless goldenrod toxin. The toxicity of these ketone toxins have not been fully characterized nor are the pathogenesis and sequelae of poisoning completely understood. The objective of the current study was to characterize and describe the clinical and pathologic changes of rayless goldenrod toxicity in goats. Fifteen goats were gavaged with rayless goldenrod to obtain benzofuran ketone doses of 0, 10, 20, 40, and 60 mg/kg/day. After 7 treatment days, the goats were euthanized, necropsied, and tissues were processed for microscopic studies. After 5 or 6 days of treatment, the 40-mg/kg and 60-mg/kg goats were reluctant to move, stood with an erect stance, and became exercise intolerant. They had increased resting heart rate, prolonged recovery following exercise, and increased serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and creatinine kinase activities. All treated animals developed skeletal myopathy with dose-related distribution and severity. The goats dosed with 20 mg/kg and higher also developed myocardial degeneration and necrosis. Although skeletal myonecrosis was patchy and widely distributed, the quadriceps femoris was consistently damaged, even in low-dosed animals. Myocardial lesions were most severe in the papillary muscles of 60-mg/kg-dosed animals. This indicates that goats are highly susceptible to rayless goldenrod poisoning, and that the characteristic lesion of poisoning is skeletal and cardiac myonecrosis.