Pteridium aquilinum (L ) Kuhn—Bracken fern; brake fern
FAMILY: Polypodiaceae—the Fern Family
This large family of ferns is delimited by the technical characters of the spore-bearing structures found either on the underside of fronds, or as separate, modified leaves.
PHENOLOGY: Pteridium produces spores in the summer.
DISTRIBUTION: Found in woods, thickets, clearings, and burned areas.
PLANT CHARACTERISTICS: Bracken grows 5-15 dm tall; stem: long, stout erect, with a more spreading blade; blade: ternate and 2-3 times pinnately compound; pinnae: opposite or nearly so; spores: tetrahedral; rhizome: blackish, widely creeping with septate hairs, not scaly; fronds: leathery and deciduous.
POISONOUS PARTS: The entire plant is poisonous in a fresh or dried condition; dead fronds apparently are not harmful.
SYMPTOMS: Horses (and monogastric animals) show anorexia, bradycardia, and incoordination. The animal may crouch with feet apart and back and neck arched. With severe signs there is tachycardia; death occurs with clonic spasms. In ruminants (sheep and cattle) one can see a rough coat, listless attitude, and mucous nasal and oral discharges (possibly bloody) about one week before the serious symptoms occur. In acute cases, an elevated temperature appears. Also there is anorexia and blood in excreta. In a prolonged illness, emaciation, hematuria, and rarely icterus can be observed. In young cattle, there is edematous swelling in the neck region with difficult breathing and death.
Postmortem: gross lesions: in monogastric animals: no significant gross lesions; enteritis with pericardial and epicardial hemorrhages; in ruminants: widespread petechiae and ecchymoses on serosal surfaces, mucosa, heart. muscles, and subautaneous tissue. Abomasal ecchymoses may lead to ulceration; anemia and aplastic bone marrow are present; histological lesions: in monogastric animals: similar to those recorded for Equisetum poisoning; in ruminants: bladder lesions, ureters, or renal pelvis representing chronic severe hyperplasia and hemorrhagic inflammation that may lead to neoplasia. The transitional epithelium has a localized proliferation with metaplasia to mucinous columnar or stratified squamous types, or a combination of both. Hyperplastic epithelium develops neoplastic properties, transforming into a squamous cell or adeno carcinoma that is locally invasive and may spread to regional lymph nodes and lung. Hemorrhage in the urine may be a result of capillaries in the inflammatory lesion becoming hyperplastic and forming hemangiomas in the stroma or on the mucosal surface.
POISONOUS PRINCIPLES: The enzyme thiaminase is suspected in horses. In ruminants the agent of toxicosis is not known but causes hypoplasia or aplasia of hematopoietic tissue.
CONFUSED TAXA: This is the only fern that produces tall, large, coarse fronds from forking, extensively creeping rhizomes.
TREATMENT: Monogastric animals require thiamine treatment. Ruminants are treated with batyl alcohol, antibiotic, antibeparin, and antihistamine.
SPECIES OF ANIMAL AFFECTED: Horses, cattle, sheep, and possibly swine are susceptible.
OF INTEREST: It may take one to three months after ingestion for signs or symptoms to be manifest in thiamine-deficient animals. Six pounds per day for one month will poison a horse. Cattle fed hay with 50% bracken for 30-80 days will be poisoned; more is needed to poison sheep.
Other ferns known or suspected to be poisonous include sensitive fern (Onoclea sensibilis L ). which may produce nervous disorders (horses) and the male fern (Dryopteris felixmas (L.) Schott ), which is suspected to contain thiaminase.