Onion / Shallot
Allium cepa / Allium ascalonicum
Horse
Severe
Any suspected ingestion is an immediate veterinary emergency. Consumption of several bulbs over a few days (often via a compost pile).
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote. Symptomatic and supportive treatment: blood transfusion, intravenous fluids, oxygen therapy.
- Time to signs
- 24 to 72 hours
- Prognosis
- Guarded if anemia is rapid and causes kidney shutdown. Good if detected early (dark urine is the first warning sign).
- Immediately remove the source of ingestion.
- Ensure complete rest for the animal.
- Contact a veterinarian urgently.
- Prepare for blood sampling.
- Blood transfusion if necessary.
Its ID card
- Height
- 30 cm – 1,2 m
- Flowering
- June to August
- Toxic parts
- Primarily the bulb (even when cooked!), as well as the green tops (leaves).
- Toxin
- Organosulfur compounds (n-propyl disulfide)
- Habitat
- Kitchen gardens, illegal dumps, accessible manure/compost piles.
- Soil indicator
- Rich, cultivated soils.
- Regions
- Entire Europe (Cultivation and culinary waste)
- In hay
- Yes — stays toxic once dried
- Palatability
- Variable. Most horses dislike it, but some curious or hungry individuals (especially in winter) may eat it with other vegetables, or even develop a taste for sweet onion.
When the risk rises
Winter (period of scarcity and access to manure piles rich in kitchen scraps).
Spotting it in the field
None, the smell is characteristic. — smell : strong, characteristic acrid smell when crushed.
- Well-known globular bulb.
- Hollow tubular stems.
- Characteristic strong odor.
- Green, hollow, cylindrical foliage.
Signs to watch for
Both acute and chronic (cumulative) toxicity
Dose : The toxic dose varies considerably, but regular ingestion of small amounts (e.g, kitchen scraps in manure) over several days can be more dangerous than a single large ingestion. For a 500 kg horse, a few bulbs (approximately 200-300g) ingested over a short period can be sufficient to trigger significant toxicity. Toxicity is cumulative.
- Dark brown to black urine (coffee grounds, severe hematuria)
- Yellowish (jaundice) or very pale mucous membranes
- Exhaustion at the slightest effort, tachycardia (heart racing)
- Strong onion smell on breath and feces
- Mild colic
Who is affected
Other species : Extremely deadly for dogs and cats (1 small onion can kill a dog).
In pregnant mares : abortion possible due to anoxia (lack of oxygen for the fetus).
Getting rid of it
Method : Pull bulbs before flowering to prevent seed dispersal. Burn plant waste to destroy toxic compounds. Ensure rigorous management of kitchen waste.
- Never discard onion, shallot, or garlic scraps in areas accessible to horses.
- Secure compost and manure piles to prevent horse access.
- Educate staff and visitors about the dangers of onions to horses.
- Monitor horses closely, especially in winter when they are more likely to seek alternative food sources.
Frequently asked questions
Can Equio identify Onion / Shallot from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Onion / Shallot 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.