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.
Horses, cattle, sheep, pigs, and humans.
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)
4. Digestive tract cancers are quite common in certain societies where bracken fern is is regulary eaten. The young fronds ('fiddle heads'), that have the highest concentration of the carcinogen ptaquilaside, are a delicacy of some Oriental peoples. Ptaquiloside is a carcinogen found 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 under side, lining the leaf margins.A distintive 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 in people has been associated with eating the uncooked bracken fern new growths
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.
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.
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).
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.
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 post mortem examination, there is usually multiple, diffuse hemorrhaging involving all organs.
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')
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