This article has not yet been professionally approved. The information is based on the sources listed below.
Poisonous plants for horses: recognising ragwort and others
Which poisonous plants on pasture, verges and in hay are most dangerous for horses, why ragwort in hay is so treacherous and how to prevent problems.
The short answer
The most dangerous poisonous plants for horses include ragwort, autumn crocus, yew and sycamore 1. Ragwort remains poisonous in hay and silage, but no longer tastes bitter there 2. The liver damage develops gradually from many small amounts 3. So check pasture and hay regularly and call your vet immediately if you suspect poisoning.
Overview of the most important poisonous plants
The Bavarian State Research Center for Agriculture (LfL) lists the most common poisonous plants for horses with their location and risk level 1. A selection:
| Plant | Where it grows | Risk |
|---|---|---|
| Ragwort | Verges, dry pastures | extremely poisonous |
| Autumn crocus | Meadows in low mountain ranges and the Alpine foothills | extremely poisonous |
| Yew | Woodland edges, hedges, gardens | extremely poisonous |
| Thuja | Hedges and gardens | extremely poisonous |
| Sycamore | Seeds, seedlings on damp pastures | highly poisonous |
| Bracken | Woodland meadows, woodland edges | highly poisonous |
| Meadow buttercup | Damp meadows, only poisonous when fresh | poisonous |
Selection from the LfL overview based on Kamphues and colleagues; risk level as stated there 1.
Ragwort: why it is so treacherous
Ragwort contains pyrrolizidine alkaloids. Horses are particularly sensitive to these substances 34.
The danger lies less in single large amounts than in many small ones. The liver damage accumulates with every intake and is irreversible 3. Signs of disease often only appear weeks to months later; in horses, neurological signs caused by liver failure, such as head pressing, are the most prominent 3.
Poisonous in hay too
When hay is made, the bitter compounds break down, but the toxins remain. Ensiling does not reduce the content either 2. Because the smell and bitterness are missing, horses eat the plant along with the hay 4.
This does not only apply to ragwort. Autumn crocus and marsh horsetail remain poisonous in hay and silage. Meadow buttercup, on the other hand, is only poisonous when fresh 4.
Prevention on pasture
The fact sheet from the German Federal Institute for Risk Assessment (BfR) names these steps against ragwort 2:
- Maintain a closed sward and reseed gaps.
- Mow areas before the seeds ripen.
- Dig out individual plants including the root.
- Avoid a shortage of feed on pasture, because horses will then also eat poisonous plants.
- Check hay and silage.
How big is the risk?
The European Food Safety Authority rates the risk of pyrrolizidine alkaloid poisoning for livestock and companion animals in the EU as generally low 5. However, the consequences for an affected horse are severe 3.
Since June 2026, the European Commission has recommended monitoring these substances in feed, including in hay, grass silage, lucerne and herbs. Horses are considered possibly more exposed because of their lucerne intake 6.
If you suspect poisoning
If your horse has eaten a poisonous plant or shows signs of illness, call your vet immediately. If possible, take the suspected plant or a sample of the feed with you. Until it has been clarified, do not feed any hay from the same batch.
Key takeaways
Frequently asked questions
Is ragwort in hay poisonous?
Yes. Drying breaks down the bitter compounds, but the toxins remain 2. This is why horses no longer avoid the plant in hay 4.
Which plants are most poisonous to horses?
In the LfL overview, ragwort, autumn crocus, yew, monkshood, foxglove and thuja, among others, are in the highest risk category 1.
How quickly does ragwort poisoning show?
Often only weeks to months after the horse started eating it, sometimes even after it is no longer eating the plants. Horses with clear signs of disease rarely recover 3.
Do horses eat poisonous plants voluntarily?
On pasture, they avoid many poisonous plants, but not always. When feed is scarce, horses will also eat ragwort, and animals without grazing experience often do not avoid poisonous plants 2.
Sources & studies
The content is based on the references listed below. It does not replace individual veterinary or feeding advice.
Show list of sources (6)
- Bayerische Landesanstalt für Landwirtschaft (LfL): Gruber Tabelle zur PferdefütterungPractical reference table with requirement and feed values based on the GfE recommendations; the basis of many ration calculations in German-speaking countries. Chapter 9.3, Table 39: most common poisonous plants for horses with habitat, toxicity and risk level (after Kamphues et al. 2014)
- Bundesinstitut für Risikobewertung (BfR): Jakobskreuzkraut – Vorbeugung und Bekämpfung auf Pferdeweiden. MerkblattOfficial leaflet (undated, image credits up to 2014): during haymaking the bitter substances break down but the toxins remain. Ensiling does not reduce the PA content. Long-term intake can cause severe liver damage. Animals without grazing experience often do not avoid poisonous plants; when feed is short, horses eat common ragwort. Recommendations: closed sward, overseeding, mowing before seeds ripen, digging out individual plants with the root, checking hay and silage
- Bildfell R (2022): Pyrrolizidine Alkaloidosis in Animals. Merck Veterinary ManualSpecialist overview, full review April 2022, updated September 2024: cattle, horses, farmed deer and pigs are the most susceptible. The liver shows the cumulative, progressive effects of repeated small doses; hepatocyte enlargement (megalocytosis) is irreversible and pronounced in horses. Poisoning also via hay, silage and pellets; at least some of the toxins survive drying. Symptoms often appear only weeks to months after intake begins, even after it has ended; in horses mainly hepatic encephalopathy (e.g. head pressing). Animals with clinical signs rarely recover. Senecio jacobaea contains jacobine
- Steilen C, Hergenröther K (2020): Giftpflanzen im Grünland. Dienstleistungszentrum Ländlicher Raum (DLR) Eifel, Bitburg, September 2020State authority of Rhineland-Palatinate. Common ragwort (pp. 6–8): horses are the most sensitive, followed by cattle. In hay and silage the deterrent smell is lost but the toxicity remains; the alkaloids are not broken down by drying or ensiling. Chronic poisoning, because the toxins accumulate in the liver; even small amounts can be fatal; chances of recovery are low. Autumn crocus (pp. 13–14): horses very sensitive, toxicity not reduced in hay and silage. Marsh horsetail (p. 16): as few as 1–3 shoots/m² can be harmful to fatal when grazed; the effect remains in hay and silage. Meadow buttercup (pp. 16–17): poisonous when fresh, no longer in hay
- EFSA Panel on Contaminants in the Food Chain (CONTAM) (2011): Scientific Opinion on Pyrrolizidine alkaloids in food and feed. EFSA Journal 9(11):2406EFSA risk assessment. According to the abstract, the risk of PA poisoning for farm and companion animals in the EU is generally low; most recently reported poisonings are due to accidental exposure. Abstract only (DOAJ) checked
- Empfehlung (EU) 2026/1210 der Kommission vom 9. Juni 2026 zur Überwachung des Vorkommens von Pyrrolizidinalkaloiden in Futtermitteln. ABl. L 2026/1210 vom 10.06.2026Recitals: all animal species are susceptible to acute and chronic PA poisoning; horses and rabbits may be more exposed because of high lucerne intake; the risk in the EU is generally considered low. Member States are to monitor, among other things, grass silage, hay, dried forage (lucerne, sainfoin), herbs and herbal extracts from PA-containing plants and compound feed containing herbs; 27 PAs including senecionine; limit of quantification 10 µg/kg; results to EFSA by 30 June 2028. Content checked via the BOE copy of the Official Journal (Spanish version)