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Bracken Fern or Brake Fern (Pteridium aquilinum)

| Description | Distribution | Conditions of poisoning | Control | Toxic principle | Clinical signs | References

Bracken Fern or Brake Fern


Bracken fern is a typical fern. Its large triangular fronds are divided into three main parts with each part bipinnately subdivided. These fronds are 2 to 4 feet long by 1 to 3 feet wide. They are borne at the tips of erect, rigid, straw-colored, smooth stalks 1 to 3 feet tall. The stalks rise at intervals from stout black underground rootstocks sometimes a yard or more long.

Spores are borne in late summer at the edges on the lower sides of mature fronds, and the edges fold under to form the spore cover. The rootstocks also spread the fern.


Many varieties of bracken fern are found throughout the U.S., particularly in dry pastures and meadows, abandoned fields, and open woods on sandy and gravelly soil. In Illinois it may be a pest throughout the northern third of the state.

Even when there is no bracken fern in the open pastures, it may be growing in the fencerows and along roadsides, where animals may browse it when other forage is scarce.

Conditions of poisoning

In dry, hot seasons or in late summer to early fall, when succulent herbage is scarce, animals more often eat bracken, although they generally avoid it at other times. Also, if hay is cut from bracken fern-infested meadows and fed, poisoning may result. Both cattle and horses are susceptible to bracken fern poisoning. Sheep and swine rarely eat bracken fern, but exposed swine (at least) may sometimes experience a thiaminase-mediated syndrome.


Especially during dry periods, animals should be kept out of bracken fern-infested pastures. Hay from infested meadows should not be used for feed or bedding. Generally bracken fern should be eliminated from pastures and hayfields. Large infestations of bracken fern may be reduced gradually by pulling or mowing the fronds twice a year (in June and August) or by fertilizing and liming infested areas.

Toxic principle

Thiaminase from bracken fern especially affects horses and pigs but not cattle. Ptaquiloside affects cattle and sheep and causes bone marrow damage. Other toxic principles that affect cattle are: aplastic anemia factor, and hematuria causing factor.

Clinical signs

Bracken fern poisoning affects the cow and the horse differently with regard to both clinical signs of illness and tissue damage.

In cattle:

After feeding on bracken fern for several to many days, cattle often sicken rather suddenly and, contrary to their reaction to most types of plant poisoning, they may show a very high fever. Major effects of bracken fern poisoning in cattle are related to damage to the blood forming elements (decreases production of white blood cells, red blood cells, and platelets) and sometimes to urinary tract carcinogenesis. Clinical signs may include rapid loss of body weight, difficult breathing, excessive salivation, bleeding from the nose, blood in the droppings, and congested, hemorrhagic, or icteric (jaundiced or yellowish) mucous membranes may also be observed. Bracken fern poisoning has been mistaken for anthrax and other infectious diseases of cattle.

In horses:

The first clinical signs of bracken fern poisoning in horses are usually an unsteady gait, a "tucked up" appearance of the flanks, nervousness, timidity, congestion of the visible mucous membranes, and constipation. Later, the horse may stand with legs spread, walking with a staggering gait, and occasionally fall, especially if its head is raised suddenly. The appetite may remain normal. Dilated pupils and both increased and decreased heart action have been reported in cases of equine bracken fern poisoning. If not treated, death occurs in 2-10 days, though some horses occasionally survive up to 30 days or more after onset of poisoning.

Other References:

Pteridium aquilinum entry in Wikipedia

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