Bigleaf Hydrangea
Hydrangea macrophylla
Horse
Moderate
Any suspected ingestion is an immediate veterinary emergency.
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote for cyanogenic glycosides. Symptomatic and supportive treatment (oxygen therapy, IV fluids).
- Time to signs
- 15 minutes to a few hours.
- Prognosis
- Generally good. Digestive disturbances are treatable if caught early. Fatal cases are very exceptional in adults.
- Immediately remove the plant from ingestion.
- Administer activated charcoal.
- Treat colic with antispasmodics.
- Close monitoring of respiration.
Its ID card
- Height
- 0.5 m – 3 m
- Flowering
- June to September.
- Toxic parts
- Entire plant, especially leaves, spring buds, and flowers.
- Toxin
- Cyanogenic glycosides (Hydrangin) and saponins.
- Habitat
- Gardens, parks, borders of houses, acidic and moist soils.
- Soil indicator
- Acidic soils (heather soil), moist, shaded.
- Regions
- Western Europe, Atlantic Coasts, Gardens everywhere
- In hay
- Yes — stays toxic once dried
- Palatability
- Medium. Poisoning almost always occurs via garden trimmings offered out of ignorance.
When the risk rises
Spring (buds are rich in toxins) and Summer (flowers).
Spotting it in the field
Guelder Rose (Viburnum opulus) - has flat white inflorescences and is also toxic. — smell : odorless.
- Bushy shrub.
- Large, ovate, toothed, bright green leaves.
- Enormous spherical (or flat) flower heads.
- Pink, blue, or white flowers depending on soil acidity.
Signs to watch for
Acute toxicity.
Dose : Difficult to estimate precisely, but several kilograms of leaves or buds are needed for severe cyanide poisoning in an adult horse.
- Gagging/vomiting efforts (horses cannot vomit, resulting in painful spasms)
- Colic and sometimes bloody diarrhea
- Panting and difficult breathing
- Accelerated heart rate
- General weakness and depression
Who is affected
Other species : Toxic to dogs and cats that chew the leaves.
In pregnant mares : risk of fetal anoxia (lack of oxygen due to cyanide) and abortion.
Getting rid of it
Method : Uproot the entire plant, including roots, and destroy by incineration. Wear gloves when handling the plant.
- Never allow horses access to areas where hydrangeas are planted.
- Dispose of hydrangea pruning waste far from pastures.
- Identify and remove hydrangeas from fence lines.
Frequently asked questions
Can Equio identify Bigleaf Hydrangea from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Bigleaf Hydrangea 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.