The plant Senecio jacobaea (tansy ragwort) produces several macrocyclic pyrrolizidine alkaloids which cause irreversible liver cirrhosis. All of the pyrrolizidine alkaloids in Senecio jacobaea are macrocyclic diesters of the necine base retronecine, with the two most predominant being seneciphylline and jacobine. Unlike horses and cattle, sheep and goats are generally...