Bracken Fern
Pteridium aquilinum
Horse
Severe
Any suspected ingestion is an immediate veterinary emergency. Chronic intoxication: high consumption over 1 to 2 months (often when pastures are severely lacking grass).
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- Vitamin B1 (thiamine) administered intravenously or intramuscularly. Supportive care.
- Time to signs
- Several weeks to several months of chronic exposure
- Prognosis
- Good if B1 deficiency is compensated quickly. Fatal if advanced paralysis is left untreated.
- Call veterinarian urgently.
- Massive Vitamin B1 injections intravenously or intramuscularly.
- Treatment over several days.
- Close monitoring of neurological symptoms.
Its ID card
- Height
- 30 cm – 2 m
- Flowering
- June to September (sporadic, reproduction is mainly by spores and rhizomes).
- Toxic parts
- Entire plant (including rhizomes).
- Toxin
- Enzyme (Thiaminase I) and Ptaquiloside (carcinogenic).
- Habitat
- Clearings, light woodlands, forest edges, heathlands, acidic and poor soils.
- Soil indicator
- Acidic, poor, sandy soils, often deforested.
- Regions
- Cosmopolitan, all of Europe
- In hay
- Yes — stays toxic once dried
- Palatability
- Normally avoided, but eaten during severe drought or in hay.
When the risk rises
Late summer and Autumn (grass drought), year-round in hay.
Spotting it in the field
Male fern (which grows more in isolated clumps, also toxic). — smell : acrid and characteristic smell when crushed or cut.
- Large fern (up to 2m).
- Very large, triangular, and divided fronds.
- Often grows in vast, dense colonies.
- Characteristic feathery appearance.
Signs to watch for
Predominantly chronic (cumulative) toxicity, but acute cases are possible with massive ingestion.
Dose : Lethal dose varies considerably depending on exposure duration and plant form (fresh or dried). Intoxication is often chronic.
- Weight loss despite good appetite initially
- Staggering gait, ataxia (loss of balance)
- Arched back and wide-based stance
- Muscle tremors
- Convulsions and inability to rise in final stage
Who is affected
Other species : Toxic to cattle (hematuria, cancers) and sheep.
In pregnant mares : can cross the placental barrier.
Getting rid of it
Method : Repeated and deep mowing to exhaust the rhizome. Pull young shoots before fruiting. Use selective herbicides if necessary, respecting withdrawal periods before grazing.
- Avoid grazing in areas infested with bracken fern.
- Manage pastures to prevent periods of grass scarcity.
- Never include bracken fern in hay.
- Closely monitor horses during droughts.
Frequently asked questions
Can Equio identify Bracken Fern from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Bracken Fern dangerous in hay?
This entry flags hay vigilance. Isolate suspicious forage and ask for professional advice if exposure is possible.
This page is informational. If ingestion is likely, if signs appear, or if the horse is fragile, contact a veterinarian immediately.