Annual Mercury
Mercurialis annua
Horse
Severe
Any suspected ingestion is an immediate veterinary emergency. High consumption over several consecutive days (often subacute intoxication).
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote. Symptomatic and supportive treatment: aggressive fluid therapy, gastric protectants, activated charcoal if recent ingestion, renal monitoring.
- Time to signs
- 12 to 48 hours
- Prognosis
- Guarded. If the kidneys are too damaged by hemoglobin, death from uremia can occur within a few days.
- Veterinary emergency.
- Gastric protectants.
- Purgatives.
- Aggressive fluid therapy (IV infusion) to 'flush' the kidneys and stop urinary hemorrhage.
Its ID card
- Height
- 30 cm – 1 m
- Flowering
- June to October.
- Toxic parts
- Entire plant (especially seeds and fresh leaves). Loses much of its toxicity when dried.
- Toxin
- Saponins (Hermidine) and alkaloids (Mercurialine)
- Habitat
- Wasteland, market gardens, cultivated fields (corn, beetroot), path borders.
- Soil indicator
- Soils very rich in nitrogen, disturbed soils, gardens.
- Regions
- Temperate Europe, Mediterranean Basin
- In hay
- Not reported
- Palatability
- Normally avoided. Consumed due to lack of forage or in a very degraded pasture invaded by weeds.
When the risk rises
June to October.
Spotting it in the field
White dead-nettle, other common weeds (but has a characteristic fetid odor when crushed). — smell : strong, acrid, slightly fetid odor when crushed.
- Small plant (30-40cm).
- Square stem.
- Opposite, oval, toothed, light green leaves.
- Tiny, greenish flowers (inconspicuous).
Signs to watch for
Cumulative (chronic) toxicity from repeated consumption over several days.
Dose : The exact quantity is difficult to determine and depends on the freshness of the plant and individual sensitivity. Significant consumption over several days is necessary. For a 500 kg horse, several kilograms of fresh plant ingested over a short period can be dangerous.
- Bloody or very red urine (constant hematuria)
- Foul-smelling greenish then blackish diarrhea
- Moderate fever
- Pale mucous membranes (anemia)
- Hindquarters weakness and prostration
Who is affected
Other species : Toxic to cattle and sheep (sheep are particularly sensitive).
In pregnant mares : very high risk of abortion (anemia and shock).
Getting rid of it
Method : Manual pulling (wearing gloves) before flowering and seed production. Avoid mowing which can spread the plant. Burn plant waste to destroy seeds.
- Regularly inspect paddocks and field borders to identify and eradicate the plant.
- Ensure sufficient and good quality forage to prevent horses from seeking out undesirable plants.
- Avoid letting horses graze in areas where the plant is present, especially after crop harvesting.
Frequently asked questions
Can Equio identify Annual Mercury from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Annual Mercury dangerous in hay?
Hay risk is not always reported for this entry, but suspicious forage should still be isolated until checked.
This page is informational. If ingestion is likely, if signs appear, or if the horse is fragile, contact a veterinarian immediately.