Common weeds poisonous to grazing livestock

Identify the common weeds in Ontario that can poison livestock.

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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 Image	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 Image	wet pastures stream banks pond edges lake edges wet ditches edges of wet woods	cattle horses sheep goats
Bracken Fern* Pteridium aquilinum Image	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
Bracken Fern* Pteridium aquilinum Image	open fields woodlands low ground dry, rocky soil	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 Image	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 Image	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 Image	(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 Image	wet areas	cattle	acute inflammation of the gastro-intestinal 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 Image	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 Image	fence rows open woods	cattle	same as with march arrow-grass poisoning
Lupine Lupinus polyphyllus Image	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 Image	roadsides pastures	horses cattle	photo- sensitivity 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 Image	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 unconscious death
Jimsonweed Datura stramonium Image	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 Image	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 Image	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 Image	bogs wet evergreen woods	cattle sheep goats	drooling watery eyes runny nose vomiting complete or partial blindness drowsiness convulsions paralysis
Tansy Ragwort* Senecio sp. Image	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 Image	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 Image	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
White Snakeroot Eupatorium rugosum Image		sheep	above, except sheep stand with legs apart
Cocklebur* Xanthium chinensis Image	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 Image	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. Image	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

Updated: March 14, 2024

Published: July 20, 2022