Clinically such animals are lethargic with accumulations of fluid or edema in the abdominal cavity. Animals with hepatic failure may show central nervous system effects including impaired vision, belligerency, and an incessant stumbling walk. As these animals develop the disease months after toxin ingestion, and the clinical signs are similar to other infectious, toxic and immunologic diseases that cause chronic liver disease, obtaining a definitive diagnosis is often impossible. Animals that develop clinical disease generally die several days later. Cattle eating 5 percent or more of their total daily diet of mature plant for periods exceeding 15 consecutive days can be expected to die within one to six months.
Sheep are more resistant to pyrrolizidine alkaloid intoxication than are cattle.
Some animals that ingest these toxins do not develop disease. Little is know of these subclinical poisonings. It is likely that such animals perform poorly throughout their lives and are culled because they are inefficient producers. Young animals are more easily poisoned than mature animals. When plants are spread over large areas and herbicide treatment may not be economically feasible.