Redroot Pigweed
Amaranthus retroflexus
Horse
Moderate
Any suspected ingestion is an immediate veterinary emergency. A very large consumption (several kilograms) over several days, typical of overgrazed pastures where only pigweed survives in summer.
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote. Intravenous fluid therapy, calcium supplementation, and symptomatic management.
- Time to signs
- A few hours to a few days
- Prognosis
- Guarded if kidney failure is triggered. Good if stopped in time.
- Remove the horse from the contaminated area.
- Contact a veterinarian immediately.
- Monitor for clinical signs.
- Veterinary blood and kidney panel.
Its ID card
- Height
- 30 cm – 1.2 m
- Flowering
- July to October
- Toxic parts
- Entire plant (stems and leaves accumulate toxins).
- Toxin
- Nitrates and Oxalates
- Habitat
- Summer crops (corn, sunflower), vegetable gardens, dry wastelands, near manure piles.
- Soil indicator
- Soils very rich in nitrogen/manure, tolerates drought very well.
- Regions
- Entire Europe (Cosmopolitan)
- In hay
- Yes — stays toxic once dried
- Palatability
- Good when the plant is young, making it all the more dangerous. It becomes rough and unpalatable as it ages.
When the risk rises
August to October (when it is saturated with nitrates).
Spotting it in the field
Lambsquarters (Chenopodium album) — smell : odorless or a slight herbaceous smell.
- Vigorous herbaceous plant (up to 1m).
- Stem often reddish at the base, hairy.
- Oval leaves, light green to grayish, with prominent veins underneath.
- Inflorescences in dense, rough, prickly spikes (small green brushes).
Signs to watch for
Both acute and chronic (cumulative) toxicity due to nitrate accumulation.
Dose : Several kilograms of fresh plant ingested over several days. The exact amount depends on nitrate/oxalate concentration and individual horse sensitivity.
- Muscle weakness and tremors (calcium drop due to oxalates)
- Cloudy or bloody urine (crystals in kidneys)
- Difficult breathing, very dark colored blood (nitrate poisoning)
- Edema (swelling) under the belly
- Incoordination (ataxia)
Who is affected
Other species : Lethal to cattle and pigs (fulminant nitrate poisoning).
In pregnant mares : nitrates block oxygenation of the fetus, leading to abortion.
Getting rid of it
Method : Hand-pull before flowering, wearing gloves. Mow infested areas before seeding. Avoid overgrazing.
- Inspect pastures and hay areas for pigweed, especially in late summer.
- Avoid overgrazing, which can promote weed growth.
- Ensure a balanced diet to reduce the temptation to eat toxic plants.
- Mow or pull pigweed before it goes to seed.
Frequently asked questions
Can Equio identify Redroot Pigweed from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Redroot Pigweed 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.