Perennial ryegrass Toxic?

Updated 2026-03-06| 3 min read| 4,530 found this helpful

Only ryegrass infected with invisible endophytic fungi is toxic, with 87% of tested German populations carrying the endophyte

Toxicity stems from indole alkaloid Lolitrem B and ergot alkaloid Ergopeptin Ergov produced by the fungus

Most affected animals recover fully within 10 days of stopping consumption of infected plant material

FAQ

Is Perennial ryegrass toxic to Humans?

No documented toxicity symptoms in humans per available data (Non-toxic)

Is Perennial ryegrass toxic to Cats?

No documented toxicity symptoms in cats per available data (Non-toxic)

Is Perennial ryegrass toxic to Dogs?

No documented toxicity symptoms in dogs per available data (Non-toxic)

Is Perennial ryegrass toxic to Horses?

Mild cases present with muscle tremors in the neck, shoulders, and flanks; severe cases involve full-body tremors, extended immobility, and impaired gastrointestinal motility (Low)

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Toxicity Details

Humans

Non-toxic

No documented toxicity symptoms in humans per available data

Cats

Non-toxic

No documented toxicity symptoms in cats per available data

Dogs

Non-toxic

No documented toxicity symptoms in dogs per available data

Horses

Low

Mild cases present with muscle tremors in the neck, shoulders, and flanks; severe cases involve full-body tremors, extended immobility, and impaired gastrointestinal motility

Toxicity Snapshot

Toxic PartsOnly plant specimens infected with the endophytic fungus Epichloë festucae var. lolii are toxic

Exposure RouteIngestion of infected plant material, typically via contaminated forage or feed

Toxic CompoundsLolitrem B (diterpene indole alkaloid); Ergopeptin Ergov (ergot alkaloid)

First Aid & Prevention

First 30 Minutes

• Immediately remove all suspected infected ryegrass forage/feed from animal access
• Move affected animals to a quiet, low-stress resting area to avoid exacerbating tremors
• Collect a sample of consumed plant material for endophyte infection testing

Contact Vet Immediately

• Animal displays visible muscle tremors, difficulty moving, or loss of coordination
• Animal has reduced appetite, abdominal discomfort, or reduced gastrointestinal motility
• Symptoms persist more than 24 hours after removing access to suspect ryegrass

Prevention

• Test pasture ryegrass populations for endophyte infection before allowing livestock grazing
• Use certified endophyte-free perennial ryegrass seed when planting forage pastures
• Monitor grazing livestock regularly for early signs of tremors or mobility issues

Treatment & Prognosis

• Administer veterinarian-directed gastrointestinal decontamination for recent large ingestions
• Provide supportive symptomatic care to manage tremors and correct gastrointestinal dysfunction
• Ensure continuous access to clean water and unrestricted rest until symptoms fully resolve

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Professional Toxicology

Scientific NameLolium perenne L.

AliasesEnglish ryegrass、Winter ryegrass

Toxicity Grade

HumansNon-toxic

CatsNon-toxic

DogsNon-toxic

HorsesLow

Target Organs

Nervous systemGastrointestinal tractMusculature

Mechanism of Action

• Endophytic fungus Epichloë festucae var. lolii lives invisibly in intercellular spaces of the plant, producing toxic alkaloids

• Lolitrem B disrupts normal neuromuscular function to cause tremors, and reduces gastrointestinal tract motility

• The fungus is transmitted to new plants via infected seeds, with 87% of tested German populations carrying the endophyte

Other Species Risk (CliniTox)

Information from CliniTox veterinary text.

Cattle: Mild infections cause muscle tremors in the neck, shoulders, and flanks; severe cases lead to full-body tremors and extended immobility, with full recovery within 10 days of removing infected feed

Sheep: Develops identical neuromuscular and gastrointestinal symptoms as cattle and horses following consumption of endophyte-infected perennial ryegrass

Confusion Risk

The following plants look similar and may be confused:

Italian ryegrass Lolium multiflorum

Visually nearly identical to perennial ryegrass with overlapping forage uses and growing ranges; Italian ryegrass is an annual species, while perennial ryegrass regrows yearly

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Related Toxic Plants

Darnel ryegrass

Lolium temulentum

Moderate toxicity, contains neurotoxic alkaloids that cause disorientation, gastrointestinal distress, and seizures in humans and livestock

Johnson grass

Sorghum halepense

Moderate to High toxicity, produces cyanide and toxic nitrates that can cause fatal poisoning in grazing livestock

Bulbous canary grass

Phalaris aquatica

Moderate toxicity, contains indole alkaloids that cause neurological damage and sudden death in grazing ruminants

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Data Sources

1. CliniTox (Universität Zürich)

This information is for reference only and does not constitute medical advice. If ingestion or poisoning is suspected, seek medical or veterinary attention immediately.