Bracken
General poisoning notes:
Bracken (Pteridium aquilinium) is a native fern that grows across most of Canada. This fern has caused sickness and loss of cattle in Canada and in other countries. Cattle, sheep, and wild animals have also been poisoned after ingesting bracken. Bracken contains several chemicals that cause problems. Thiaminase results in vitamin B1 deficiency in nonruminants such as horses and swine. Ptaquiloside, a carcinogen-mutagen, causes acute and chronic symptoms of illness in ruminants. The spores may contain carcinogens that can cause problems to animals and humans. The young fronds of bracken are ingested as human food, especially in Japan. They contain significant quantities of the carcinogen (Cheeke and Schull 1985, Fenwick 1988, Hirono 1989).
Nomenclature:
Scientific Name: Pteridium aquilinum (L.) Kuhn
Vernacular name(s): bracken
Scientific family name: Polypodiaceae
Vernacular family name: frern
Pteridium aquilinum (L.) Kuhn
Geographic Information
Alberta, British Columbia, Labrador, Manitoba, New Brunswick, Newfoundland, Nova, Scotia, Ontario, Prince Edward Island, Quebec
Notes on Poisonous plant parts:
All parts of bracken contain toxic chemicals. Ingesting fresh or dry fronds (leaves) or underground rhizomes has caused toxic signs and death in ruminants and nonruminants. After ingesting the young fronds, animals were found to be affected by carcinogenic compounds that the young fronds contain; these compounds may also cause problems in humans. The spores appear to be the most carcinogenic part of bracken and may cause problems in livestock. Humans who work outdoors in areas where bracken grows abundantly could also be at risk from the spores (Milne and Fenwick 1988, Milne 1988, Hirono 1989).
Toxic parts:
All parts, leaves, rhizome, spores, young shoots
Notes on Toxic plant chemicals:
A group of chemical compounds have been implicated in the various toxic properties of bracken. Thiaminase, an enzyme that decomposes vitamin B1, has caused toxic problems, particularly in nonruminants, which cannot synthesize their own vitamin B1. Ptaquiloside and aquilide A possess an unusual, planar, illudane norsesquiterpene skeleton. Under alkaline conditions these chemicals yield pterosin B, a proximate carcinogenin-mutagen. Pterosin B has been implicated as a cause of the cancers noted after bracken ingestion, and ptaquiloside has been implicated as a contributor to the toxic signs in ruminant animals (Cheeke and Schull 1988, Fenwick 1988). Bracken also contains prunasin, a cyanogenic glycoside, which appears to be a deterrent to herbivory (Tewe and Iyayi 1989).
Toxic plant chemicals:
aquilide A
prunasin
prunasin
ptaquiloside
thiaminase
Chemical diagram(s) are courtesy of Ruth McDiarmid, Biochemistry Technician, Kamloops Range Station, Agriculture and Agri-Food Canada, Kamploops, British Columbia, Canada.
Animals/Human Poisoning:
Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.
Cattle
General symptoms of poisoning:
Anemia, bone marrow damage, cancer and tumors, death, hemorrhage
Notes on poisoning:
Consuming significant quantities of bracken fronds can cause bracken poisoning, which results in bone marrow damage. Only small foci of erythropoietic cells and some megakaryocytes remain. Hemorrhaging occurs, with blood in the feces and bleeding from the nose, vagina, and membranes around the mouth and eyes. Postmortem examination shows hemorrhaging in the stomach, intestines, lungs, and heart (Cheeke and Schull 1985, Fenwick 1988, Hirono 1989).
Horses
General symptoms of poisoning:
Anemia, anorexia, ataxia, colic, convulsions, death, gait, staggering, incoordination, opisthotonos, recumbency, weight loss
Humans
General symptoms of poisoning:
Bancer and tumors
Notes on poisoning:
The young fronds of bracken have been used as a food source, particularily in Japan. Ptaquiloside, a carcinogenic compound, has been found in bracken. The toxin is especially abundant in the young fronds. If the fronds are not processed in any way, tumor incidence in rats is 78%. After the fronds are processed with boiling water or are boiled with wood ash, sodium bicarbonate, or salt, the incidence of cancer is reduced to 4-25%. Mammary cancer and ileal and urinary bladder tumors were observed. Cattle develop urinary papilloma. The carcinogen can be transferred by milk. The high incidence of stomach cancer in Japan may be partly due to the consumption of bracken (Cheeke and Schull 1985, Hirono 1989).
Sheep
General symptoms of poisoning:
Blindness
Notes on poisoning:
Sheep in the British Isles have developed a condition called bright blindness. The sheep develop degeneration of the neuroepithelium of the retina, with low counts of blood platelets and white blood cells. This problem has been linked to the consumption of bracken. Cattle with similar symptoms have been reported (Fenwick 1989).
Swine
General symptoms of poisoning:
Appetite, loss of death
Notes on poisoning:
Reports of acute bracken poisoning in swine are infrequent, perhaps because of few symptoms. The symptoms are similar to heart failure. Experimental feeding of dry, powdered rhizomes produced loss of appetite after 8 weeks, followed by rapid deterioration and death 2 weeks later. Postmortem findings revealed damage to the heart. Ingestion by pregnant sows resulted in some death of the piglets after birth (Fenwick 1988).
