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Distinguishing features
Native perennial herb with black horizontal rhizomes deep in the soil (often below plow depth), by means of which it spreads and forms large patches; leaves 3-4 feet tall in good sites; leaf stalk forks into three main parts, producing a triangular, bipinnately pinnatifid blade; spores produced in late summer in sporangia protected by the rolled-under edges of the blade.
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| Description. Deciduous
fern with a horizontal root system that can grow up to several meters
long. |
| Geographic range.
Found throughout the United States in dry open
woodlands. Spreads rapidly due to its extensive root system. |
| Toxic principle.
Thiaminase splits the essential vitamin thiamine
(B1) into its two inactive components, pyrimidine and
thiazole, causing thiamine deficiency. |
| Toxicity. Bracken
fern is associated with poisoning of cattle, sheep, pigs, horses, and
humans. Horses must consume a diet of 3-5% bracken fern for at
least 30 days before clinical signs appear. Rhizomes are the most
toxic portion of the plant. |
| Mechanism of toxicologic
damage. Thiamine is essential in energy
metabolism and is broken down by thiaminase. Thiamine deficiency
causes CNS depression and polioencephalomalacia. |
| Diagnosis
Clinical
signs. Depression, muscle tremors,
uncoordinated gait. Retinal degeneration and blindness.
Hemorrhaging and bone marrow destruction, urinary bladder cancer, and
digestive tract cancers.
Laboratory
Diagnosis. Severe anemia may be seen.
Decreased thiamine levels and increased pyruvic acid levels are seen.
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| Treatment. Treat
horses with 5 mg/kg body weight of thiamine intravenously. Repeat
the dose intramuscularly for several days. Nursing care and
systemic antibiotics are also helpful. |
| Prevention. Feed
animals a balanced diet free of bracken fern.
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