Common Weeds Poisonous to Grazing Livestock

Table of Contents

  1. Introduction
  2. Common Weeds Poisonous to Grazing Livestock
  3. Related Links

Introduction

Livestock can be poisoned or injured by certain plants while grazing or fed in stored feed. The OMAFRA Factsheet "Poisoning of Livestock by Plants", Agdex 130/643, reviews the types of poisoning which can occur and the effects on animal health and production.

Many common weeds in Ontario can poison livestock. This Factsheet identifies these weeds and describes the symptoms of poisoning. Because some poisons act very fast (as with the hemlocks) by the time the symptoms are evident, the chances of saving the animal are very slight. It is, therefore, important to learn to recognize these weeds beforehand and prevent poisoning from occurring. Most of these weeds can be controlled chemically or mechanically. In some cases, it may be more practical to simply fence off infested areas so that the animals do not have access to particularly hazardous weeds.

It should be noted that most of these weeds are unpalatable and animals will usually not graze them if given the choice. One of the most important steps in preventing animal suffering or loss is good pasture management. Keeping the desirable forage species producing throughout the grazing season, reduces the possibility of animals grazing poisonous weeds.

If symptoms of poisoning should occur, it is recommended that you call your veterinarian as soon as possible.

Common Weeds Poisonous to Grazing Livestock

Weed Where generally located Livestock affected Symptoms
Poison Hemlock *
Conium maculatum

Poison Hemlock
  • waste areas
  • road sides
  • dry ditches
  • cattle
  • horses
  • sheep
  • goats
  • death may occur within 15 minutes
  • frothing at the mouth
  • uneasiness
  • pain
  • dilated pupils
  • clamping of jaws
  • grating of teeth
  • vomiting
  • weak, rapid pulse
  • diarrhea
  • bloating
  • convulsions
  • respiratory failure
  • death
Water Hemlock *
Cicuta maculata

Water Hemlock
  • wet pastures
  • stream banks
  • pond edges
  • lake edges
  • wet ditches
  • edges of wet woods
Bracken Fern *
Pteridium aquilinum

Bracken Fern
  • open fields
  • woodlands
  • low ground
  • dry, rocky soil
  • horses
  • symptoms are slow to develop
  • loss of flesh
  • jaundice
  • loss of appetite
  • weakness
  • staggering gait
  • excitability
  • paralysis
  • cattle
  • sheep
  • symptoms are slow to develop
  • high fever
  • labored breathing
  • drooling
  • hemorrhaging from nostrils
  • blood in urine and feces
  • convulsions
Marsh Arrow-Grass
Triglochin palustris

Marsh Arrow-Grass
  • marshes
  • alkaline soils
  • cattle
  • sheep
  • symptoms appear rapidly
  • rapid, difficult breathing
  • almond odor to breath
  • animals go down with head turned to one side
Horsetail *
Equisetum arvense

Horsetail
  • poorly drained soils
  • low, sandy, acid soils
  • cultivated fields
  • roadsides
  • waste areas
  • woods
  • horses
  • cattle
  • sheep
  • symptoms are slow to develop
  • jaundice
  • loss of appetite
  • weakness
  • staggering gait
  • excitability
  • paralysis
Pokeweed *
Phytolacca americana

Pokeweed
  • (southern Ontario only)
  • waste areas
  • meadows
  • edges of woods
  • cattle
  • symptoms occur two or more hours after plants are eaten
  • retching spasms
  • vomiting
  • purging
  • convulsions
Marsh Marigold *
Caltha palustris


  • wet areas
  • cattle
  • acute inflammation of the gastrointestinal tract
  • vomiting
  • colic
  • bloody urine
  • diarrhea
  • twitching of the eyelids
  • weak pulse
  • loud breathing
  • reduce milk production
  • tainted milk red in colour and bitter tasting
Tall Buttercup *
Ranunculus acris

Tall Buttercup
  • pastures
  • meadows
  • roadsides
  • cattle
  • horses
  • sheep
  • goats
  • inflammation and blisters where plant juice touched the animal
  • mouth blisters cause drooling and loss of appetite
  • other symptoms similar to those for marsh marigold
Wild Cherries Black
Prunus virginiana
# Choke
## Pin
Wild Cherries - Black
  • fence rows
  • open woods
  • cattle
  • same as with march arrow-grass poisoning
Lupine
Lupinus polyphyllus

Lupine
  • pastures
  • meadows
  • roadsides
  • waste areas
  • sheep
  • cattle
  • horses
  • nervousness
  • labored breathing
  • convulsions
  • frothing at the mouth
  • frenzy
  • aimless running about
Saint-John's Wort *
Hypericum perforatum

Saint-John's Wort
  • roadsides
  • pastures
  • horses
  • cattle
  • photosensitivity
  • inflammation of the unpigmented portion of the skin
  • affected area becomes sore and reddened and may peel
  • tongue and mouth may be affected
Nightshade *
Solanum sp.
# Eastern Black
## Black Hairy Climbing

Nightshade
  • open dry woods
  • cultivated fields
  • pastures
  • fence rows
  • waste areas
  • farm yards
  • cattle
  • horses
  •  
  • sheep
  • goats
  • abdominal pain
  • stupidity
  • dilation of pupils
  • loss of appetite
  • diarrhea
  • loss of muscular coordination
  • unconsciousness
  • death
Jimsonweed
Datura stramonium

Jimsonweed
  • cultivated fields
  • farm yards
  • cattle
  • horses
  •  
  • sheep
  • goats
  • dilation of the pupils
  • impaired vision
  • fast, weak pulse
  • nausea
  • loss of muscular coordination
  • violent, aggressive behaviours
  • trembling
  • milk is tainted
Milkweed *
Asclepias sp.
# Whorled
## Common

Milkweed
  • dry, open areas
  • pastures
  • around woods
  • roadsides
  • waste areas
  • cultivated fields
  • cattle
  • sheep
  • loss of appetite
  • constipation
  • drooling
  • excitable
  • difficult breathing
  • rapid, weak pulse
  • convulsions
  • death
  • horses
  • persistent colic
Cockle *
Saponaria officinalis
# Purple Cockle
## Cow Cockle Bouncingbet

Cockle
  • pastures
  • cultivated fields
  • roadsides
  • waste areas
  • horses
  • cattle
  • restlessness
  • grinding of teeth
  • drooling
  • colic
  • diarrhea
  • rapid breathing
  • weak pulse
  • coma
  • death
Laurel
Kalmia sp.
Sheep Pale or Bog

Laurel
  • bogs
  • wet evergreen woods
  • cattle
  • sheep
  • goats
  • drooling
  • watery eyes
  • runny nose
  • vomiting
  • complete or partial blindness
  • drowsiness
  • convulsions
  • paralysis
Tansy Ragwort *
Senecio sp.

Tansy Ragwort

  • pastures
  • hayfields
  • waste areas
  • roadsides
  • horses
  • cattle
  • nervousness
  • chills
  • pale mucous membranes
  • loss of coat lustre
  • strong, rapid pulse
  • high temperature
  • staggering gait
  • weakness
  • death
Spurge *
Euphorbia sp.
Cypress Leafy

Spurge
  • cultivated fields
  • waste areas
  • roadsides
  • horses
  • goats
  • cattle
  • sheep (leafy is non-toxic to sheep)
  • contact with sap
    • causes inflammation of skin
  • eating causes
    • diarrhea
    • vomiting
    • swelling around mouth and eyes
    • abdominal pains
    • muscle tremors
    • sweating
    • tainted milk has reddish colour, bitter taste
White Snakeroot
Eupatorium rugosum

White Snakeroot
  • wooded areas
  • persists after woods are thinned out
  • stream banks
  • horses
  • cattle
  • goats
  • depression
  • inactivity
  • arched body
  • hind feet place close together
  • excessive salivation
  • nasal discharge
  • nausea
  • rapid, labored breathing
  • sheep
  • above, except sheep stand with legs apart
Cocklebur *
Xanthium chinensis

Cocklebur
  • cultivated fields
  • stream banks
  • beaches
  • farm yards
  • horses
  • cattle
  • sheep
  • symptoms appear within a few hours
  • weakness
  • unsteady gait
  • twisting of neck muscles
  • depression
  • nausea
  • vomiting
  • labored breathing
  • rapid, weak pulse
  • death
Sneezeweed
Helenium automnale

Sneezeweed
  • wet areas
  • roadside ditches
  • stream banks
  • cattle
  • horses
  • sheep
  • symptoms are slow to develop
  • loss of vigor
  • loss of flesh
  • rapid pulse
  • labored breathing
  • loss of muscular control
  • drooling
  • high temperature
  • dizziness
  • spasms
  • convulsions
# Squirrel Corn
## Dutcheman's Breeches
Dicentra sp.

Squirrel Corn and Dutcheman's Breeches
  • wooded areas (maple woods)
  • cattle
  • symptoms develop 48 hours after plants are eaten
  • trembling
  • frothing at the mouth
  • vomiting
  • diarrhea
  • labored breathing
  • convulsions

* Described in Ontario Weeds, Publication 505

Related Links


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: S.E. Robinson - University of Guelph; J.F. Alex - University of Guelph
Creation Date: 01 February 1987
Last Reviewed: 01 November 2011