Common Name
Fiddleneck, tarweed, yellow bur weed
Botanic Name
Amsinckia menziesii
Plant Family
A weed of dry cultivated soils, waste areas, and commonly in wheat fields.
Animals Affected
Horses, cattle,
Fiddleneck - Amsinckia menziesii
Toxic Principle
Pyrrolizidine alkaloids (PA) inhibit cell division, primarily affecting the liver. The PAs are cumulative in effect, causing severe liver fibrosis and eventual irreversible liver failure after several months. All parts of the plant are toxic, even when it is dried. As little as 15mg of dried plant per kilogram bodyweight over 2 weeks will induce severe liver disease.
Erect, sparsely branching, 2-3 feet tall, annual weed. The entire plant is very hairy. Leaves are lanceolate and alternate. The five parted orange to yellow flowers are produced terminally on a distintive fiddleneck shaped raceme, the flowers are all inserted on one side of the axis. Fruits split open to release 2-4 black-ridged nutlets.
Diarrhea, chronic straining and even rectal prolapse may occur in chronic cases.
Weight loss
Secondary photosensitization can be alleviated by keeping the animal in a dark stall out of the sun. However, the underlying liver disease is rarely if ever successfully treatable, and the prognosis is very poor.
Nervous System
Severe depression, aimless walking, incessant licking of objects, head pressing, and other unusual behavior (hepatic encephalopathy) result from the chronic severe liver disease.
Renal System
Red colored urine has been observed in horses with severe PA induced liver disease.
Integumentary System
Secondary photosensitization develops as a result of severe liver disease. White skinned (non-pigmented) areas become red, swollen, and painful before the skin dies and sloughs-off. Photosensitization resembles a severe sunburn.
Ocular System
Photophobia may be evident especially if the skin around the eyelids is white, or the third eyelid and sclera lack pigment.
Hepatic System
Yellow coloration to the mucous membranes (jaundice), weight loss, edema of the legs, red urine (hemoglobinuria) are signs of severe liver disease.
A combination of the clinical signs with evidence that the animal has been eating a PA containing plant is highly suggestive of PA poisoning. Elevated serum liver enzymes, decreased albumin, and a liver biopsy that shows megalocytosis, fibrosis and biliary hyperplasia are diagnostic.
Special Notes
References 1. Fowler ME (1968) Pyrrolizidine alkaloid poisoning in calves. J Amer Vet Med Ass 152, 1131-7. 2. Stegelmeier BL, Edgar JA, Colegate SM, Gardner DR, Schoch TK, Coulombe RA, Molyneux RJ (1999) Pyrrolizidine alkaloid plants, metabolism and toxicity. J Natural Toxins 8, 95-116.
Fiddle neck inflorescence