Poisonous Weeds in Pastures

Poisonous Weeds in Pastures

Introduction
Livestock managers seem to have an increasing awareness that poisonous plants can affect livestock. Part of this is due to the ever increasing population of horse owners and the growth in management intensive grazing systems. Poisonous plant questions are also more frequent in dry years as droughts create situations in which animals often graze plants they would otherwise not eat and producers may harvest fields or plants that are not usually harvested to have adequate feed stock for the winter. Additionally, weeds not usually considered toxic might become poisonous under certain condition. For example, weeds may become more palatable to livestock following an herbicide application in a pasture or fencerow. This may result in animals eating plants they would normally avoid consuming. All areas of the country have different species of concern and your local extension agent or university may be of assistance.

What are the Plants That Cause Animal Poisoning?
The book “Poisonous Plans of the Midwest” (Evers and Link 1972) includes 70 species. Indiana lists 53 plants as potentially poisonous to animals on their “Indiana Plants Poisonous to Livestock and Pets” web site The Indiana Plants Poisonous to Livestock and Pets site(http://vet.purdue.edu/depts/addl/toxic/cover1.htm)

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

Species
Toxin
Comments

bracken fern
thiaminase
woods and open areas; all part poisonous

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

chokecherry
prussic acid
common in fencerows and woods

cocklebur
hydroquinone
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
unknown
horses are particularly sensitive

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

horseweed
alkaloids
seldom eaten because of spines

jimsonweed
alkaloids and others
all plant parts toxic

lambsquarters
nitrate and oxalate
common field weed; high in feed value

nightshades
solanine and other glycoalkaloids
all parts poisonous under certain condition; ripe berries almost nontoxic

oaks
gallotannins
acorns and young leaves and shoots are of concern

pigweeds
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


Excerpts taken from article by Jerry Doll, University of Wisconsin, Poisonous Weeds of Pastures & Forages