Common Name
Bracken fern, brake fern, eagle fern
Botanic Name
Pteridium aquilinum L. Kuhn
Plant Family
Moist open woodlands where it can form dense stands.
Bracken fern is widely dispersed throughout North America with most poisoning occurring in the North Western States.
Animals Affected
Horses, cattle, sheep, pigs, and humans.
Toxic Principle
Bracken fern has been associated with a variety of different syndromes in animals and people, the best recognized of which include: 1. Thiamin deficiency - an enzyme, thiaminase, in the plant causes a thiamin (vitamin B1) deficiency resulting in blindness, depression, weight loss in horses. 2. Retinal degeneration and blindness (Bright blindness) occurs in sheep eating bracken over a period months. 3. Hemorrhaging syndrome (Enzootic hematuria, red water) is encountered in cattle grazing large quantities of bracken fern over a period of months. Over time cattle develop urinary bladder tumors (hemangioma, hemangiosarcoma, adenocarcinoma) which can release blood into the urine. 4. Digestive tract cancers are quite common in certain societies where bracken fern is frequently eaten. The young fronds ('fiddle heads'), that have the highest concentration of the carcinogen ptaquilaside, are a delicacy among some groups. Ptaquiloside is a carcinogen found in the roots and new shoots of bracken. The prevalence of esophageal and stomach cancers is disproportionately high in those eating bracken fronds on a regular basis. Large quantities of bracken fern must be consumed over a period of weeks to induce poisoning. Horses eating hay containing 3-5% bracken for 30 days will be affected. The dried bracken in hay remains toxic. Ptaquilosides are present in many other species of fern that have been tested. Lactating cows grazing bracken will pass the ptaquiloside through the milk, which poses a potential risk to people drinking the milk
Herbaceous, perennial that spreads via its horizontally branching black roots. Leaves arise directly from the rhizomatous roots and may be up to 5 feet tall. The triangular leaves are bipinnate and have brown reproductive spores on the underside, lining the leaf margins. A distinctive feature of bracken fern is that the subleaflets are distinctly lobed at the base but not at the apex or tip.
Cancer of the digestive tract has been associated with eating the uncooked bracken fern new growths in people and animals.
Thiamin deficiency can be treated with large doses of thiamin. There is no effective treatment for the bone marrow depression and resulting loss of clotting factors. Blood transfusions may be helpful. Batyl alcohol may have some benefit as bone marrow stimulant.
Cardiovascular system
Cattle may develop severe bone marrow depression and depletion of platelets (thrombocytopenia) that results in a hemorrhaging disease referred to as enzootic hematuria. Affected animals usually die from hemorrhaging because they loose the ability to clot their blood.
Nervous System
Horses and pigs are most affected by the thiaminase present in bracken. Severe depression, blindness, weakness and eventual death may result from the deficiency of thiamin (vitamin B1).
Renal System
Cattle develop red colored urine (hematuria) resulting from the development of tumors (hemangiosarcomas) in the urinary bladder. Hematuria may also result from the loss of platelets and hemorrhaging into the bladder.
Ocular System
Blindness may be due to thiamine deficiency, or may in the case of sheep be due to retinal degeneration.
Diagnosis of bracken fern poisoning should be based on the history of the fern being eaten for an extended period of time, a hemorrhagic syndrome, caused by bone marrow depletion resulting in thrombocytopenia, and leukopenia. The presence of blindness (horses), or bladder tumors warrant consideration of bracken fern poisoning. At postmortem examination, there is usually disseminated hemorrhage involving most or all organs.
Special Notes
Management and Control Bracken fern is an aggressive plant and forms dense stands to the exclusion of other forages as a result of its allelopathic properties. Management of the plant requires a multifaceted approach including strategic mowing, digging out the plant, and herbicides. Herbicides that have been effective in controlling bracken fern include: Chlorthiamid, Dicamba, Picloram, and Methyl sulfanilylcarbamate('Asulam') References 1.Potter DM, Baird MS. Carcinogenic effects of ptaquiloside in bracken fern and related compounds. Br J Cancer. 2000. 83:914-920. 2.Kiyoyuki Yamada, Makoto Ojika and Hideo Kigoshi. Ptaquiloside. The major toxin of bracken and related terpene glycosides: chemistry, biology and ecology Nat. Prod. Rep. 2007, 24: 798-813 3.Hirono I et al.Reproduction of progressive retinal degeneration (Bright blindness) in sheep by the administration of ptaquiloside contained in bracken. J Vet Sci: 1993. 55: 979-983. 4.Alonso-Amelot ME, Avendano M. Human carcinogenesis and bracken fern: A review of the evidence. Current Medicinal Chemistry 2002. 9: 675-686. 5.Sippel WL. Bracken Fern Poisoning. J Am Vet Med Assoc 1952. 121: 9-13. 6.Francesco B, Giorgio B, Rosario N, et al. A new, very sensitive method of assessment of ptaquiloside, the major bracken carcinogen in the milk of farm animals. Food Chem 2011. 124: 660-665. 7.Rasmussen LH, Lauren DR, Smith BL, et al. Variation in ptaquiloside content in bracken (Pteridium esculentum (Forst. f) Cockayne) in New Zealand. N Z Vet J. 2008. 56: 304-309. 8.Carvalho T, Pinto C, Peleteiro MC. Urinary bladder lesions in bovine enzootic haematuria. J Comparative Path. 2006. 134:336-346.
Bracken fern (Pteridium aquilinum)
Bracken fern habitat
New bracken fronds ('fiddle necks')