Plants poisonous to livestock

Poisonous plants can be found in pastures and stored forages. Be sure to check your pastures for poisonous plants before turning your livestock out to graze.

Livestock can be poisoned or injured by certain plants while grazing or being fed stored feed. Many common weeds in Michigan can poison livestock. Some poisons act very fast. In these cases, by the time the symptoms are evident, the chances of saving the animal are very slight. It is 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. In the chart below are several pasture plants that are toxic to livestock. An internet search can help to visually identify these plants.

Table 1. A partial list of plants common in Michigan that are capable of affecting animal health and the causal agent (toxin) they contain.




bracken fern


 woods and open areas; all part poisonous



pastures, esp. wet areas; causes sharp drop in milk production; toxin lost on drying forage


prussic acid

common in fencerows and woods



cultivated fields, pastures; esp. sandy soils; seedlings and seeds toxic

hemp dogbane

apocynin & other glycosides

all plant parts have milky sap; fields and roadsides

hoary alyssum


horses are particularly sensitive



wet or dry areas of pastures and roadsides; all parts toxic

horse nettle


seldom eaten because of spines


alkaloids and others

all plant parts toxic


nitrate and oxalate

common field weed; high in feed value


solanine and other glycoalkaloids

all parts poisonous under certain condition; ripe berries almost nontoxic



acorns and young leaves and shoots are of concern


oxalate and nitrate

common field weed; many species; prostrate and tumble pigweed common in pastures

poison hemlock               

many alkaloids

roadsides, edges of fields and waste areas where soil is moist; all parts highly toxic

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.

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