Toxic Plants - Series 4 Article 3 - Northeastern US Plants That Can Be Toxic To Livestock
By Merry Bogert
Caveat and general statements regarding toxicity:
1) Not every toxic plant is discussed in
these articles and, just because a plant is not discussed in the article does
not mean it is not toxic.
2) Some plants are species-specific with
regards to toxicity – in other words, not all plants are toxic in the same way
with all animals or people
3)
The “poisonous plant triangle” applies to any potentially toxic plant.
This term means that three things are required for a particular plant to be
toxic:
(a) the presence of some particular chemical
in the plant, AND
(b) a susceptibility or sensitivity to that
chemical by the animal or person
ingesting or contacting the plant, AND
(c) consumption/contact with sufficient
quantity to cause a reaction.
All three must be present in order
for a plant to be toxic to an individual animal or person at one particular
point in time.
4)
Toxicity can range from dermatitis (a skin reaction, such as is seen with
poison ivy) to gastro-intestinal issues and even death.
5)
Most accidental ingestions are unintentional and often involve children
attracted to brightly colored berries, flowers, etc.
Northeastern US Plants that
can be toxic to Livestock
A
well-managed pasture is key to avoiding toxicity in grazing animals of any
kind.
Any owner of grazing livestock should monitor pastures for undesirable
weeds and take action to minimize their presence. An abundance of high quality
(and good-tasting) grasses will often confer some level of protection, since
the toxic plants often don’t taste as palatable. But as summer heats up and dry
conditions prevail, cool season grasses will languish, allowing undesirable
weeds to assume a larger proportion of edible plant material – sometimes to unfortunate
and expensive result.
The term
“toxic” does not necessarily imply deadly, although some plants are potentially
so. Among the most dangerous toxic plants, jimsonweed (Datura spp.) probably has the fastest onset of symptoms (within
minutes), with poison hemlock (Conium
maculatum) and water hemlock (Cicuta spp.)
not far behind. Symptoms include central nervous system depression, thirst,
convulsions, respiratory failure, coma, and death.
Toxic trees
include red maple (causes severe anemia), black locust (rarely fatal, but with
alarming symptoms), oak (its tannins affect the GI tract), walnut (bark and nut
hulls), and cherry (especially wilted wild cherry leaves, which release cyanide
as they are digested).
Toxic shrubs
include ornamentals such as rhododendrons/azaleas, mountain laurel, and yew. Of
these yew (Taxus) poses the greatest
threat – it can kill within thirty minutes of ingestion if only a mouthful of
the leaves is consumed by a horse. While most ornamental shrubs are not found
in pastures, sometimes clippings can be tossed into an adjacent pasture by a well-meaning
neighbor who thinks that the green leaves might be food for the grazing animals.
It is imperative that owners of livestock inform their neighbors of the danger
posed by yard clippings.
A Yew shrub. Photo by Tom Guthrie, MSU Extension
A list of
toxic ornamental plants/flowers that might be growing home gardens adjacent to
pastures is extensive and is contained in the University of Maryland
publication cited below.
Other
dangerous plants include nightshade, milkweed, hemp dogbane, pokeweed, buttercups,
soapwort, bracken fern, horsetail, and star of Bethlehem (especially the bulbs),
just to name a few.
White
snakeroot (Eupatorium rugosum) causes
trembling, weakness, excessive salivation, and constipation. Its toxic
alkaloids pass through the milk and cause milk sickness in nursing young or, as
happened with the mother of Abraham Lincoln, death from drinking the contaminated
milk.
Cocklebur (Xanthium spp.), especially the
seedlings, is very toxic and especially so for horses. Alsike clover (Trifolium hybridum) is often included in
pasture seed mixes for hay, but should be avoided if you have horses. It is one
of the plants that causes photosensitivity with blistering and oozing skin
lesions and can also cause “big liver disease” with weight loss, jaundice,
encephalopathy, and cerebral dysfunction. Soapwort/bouncing bet (Saponaria officinalis) can also cause acute
liver toxicity due to its saponins.
Johnson
grass (Sorghum halepense) is related
to sorghum and to Sudan grass, all of which contain compounds in their stems
and leaves - and especially concentrated in wilting leaves from drought or
frost - that release cyanide when digested. Called “sorghum poisoning”, it
affects horses particularly, but can also affect cattle and sheep. It is
characterized by central nervous system effects, rapid and labored breathing,
frothing at the mouth, bright red mucous membranes, muscle weakness and
twitching. Death ensues rapidly if large amounts of the affected grass have
been consumed.
I’ll end
this section the way it began: careful pasture management can prevent a lot of
problems, including unnecessary loss of livestock and high veterinary bills.
For more
information, please see the following links:
1. Cornell University’s College of
Agriculture and Life Sciences:
2. Rutgers University’s Agricultural
Experiment Station Fact Sheet on “Poisonous Weeds in Horse Pastures”: https://njaes.rutgers.edu/fs938/
3. Pennsylvania State University
Extension fact sheet “Poisonous Pasture Weeds”:
https://extension.psu.edu/poisonous-pasture-weeds
4.
University of Maryland Extension online publication has excellent
photographs that accompany each listed plant, along with the plant’s
description, poisonous parts, and signs of poisoning: https://extension.umd.edu/sites/extension.umd.edu/files/_docs/locations/frederick_county/Ag%20Pubs%20Common%20Plants%20Poisonous%20to%20Horses%20and%20Livestock%20in%20MD%20Draft%204-14.pdf
