Bishop's Weed
Ammi majus
Horse
Severe
Any suspected ingestion is an immediate veterinary emergency. Consumption of a few hundred grams of the plant (or even contaminated hay) followed by strong summer sun exposure.
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote. Supportive care, sun protection, anti-inflammatories, and analgesics.
- Time to signs
- A few hours to 24 hours after sun exposure.
- Prognosis
- Good for overall survival, but skin lesions are excruciatingly painful and slow to heal (several weeks).
- Immediately move the horse to a dark stable (without sun-exposed windows).
- Apply soothing topical treatments to the burns.
- Consult a veterinarian to assess the need for veterinary corticosteroids if edema is significant.
Its ID card
- Height
- 0.3 m – 1 m
- Flowering
- June to September.
- Toxic parts
- Entire plant, particularly seeds and leaves.
- Toxin
- Furanocoumarins (Xanthotoxin)
- Habitat
- Cultivated fields, fallow land, wastelands, roadsides, dry, calcareous soils.
- Soil indicator
- Dry, sunny, calcareous, and sandy soils.
- Regions
- Mediterranean Basin, Southern Europe, Occasionally introduced elsewhere
- In hay
- Yes — stays toxic once dried
- Palatability
- Moderate. Intoxication often occurs when pastures are dry and Ammi majus is one of the few remaining green plants, or via hay harvested in the south.
When the risk rises
June to September (flowering + strong sun).
Spotting it in the field
Wild carrot (often harmless), Poison hemlock (deadly neurological), Ammi visnaga. — smell : slightly aromatic smell, reminiscent of parsley or carrot, but more acrid when crushed.
- Erect plant (up to 1m).
- Glabrous, finely striated stem.
- Highly dissected leaves resembling carrot or flat-leaf parsley.
- Large, delicate, and branched white umbels of flowers.
Signs to watch for
Acute toxicity (photosensitization) triggered by ingestion and sun exposure.
Dose : Difficult to quantify precisely, but a few hundred grams of fresh plant or contaminated hay can be sufficient to trigger severe photosensitization in a sensitive horse.
- Severe burns (redness, blisters, necrosis) on unpigmented skin areas (muzzle, socks, around the eyes)
- Severe itching (pruritus) and pain to the touch
- Edema of the face and eyelids
- Corneal opacity (cloudy eye) if eye contact occurs
- Fever linked to skin inflammation
Who is affected
Other species : Severe photosensitization in sheep and cattle (especially light-colored breeds), as well as in humans through contact.
In pregnant mares : no major direct abortifacient risk documented.
Getting rid of it
Method : Mechanically pull the plant before flowering, wearing gloves to avoid skin contact. Destroy the uprooted plant (burning).
- Inspect pastures and hay for the presence of Ammi majus.
- Use UV-blocking masks and sunscreen for horses with light or piebald skin, especially during summer months.
- Avoid grazing horses in areas known to contain this plant, particularly during dry weather.
Frequently asked questions
Can Equio identify Bishop's Weed from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Bishop's Weed 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.