Submitted By: Krishona Martinson, Regional Extension
Educator
In early October 2004, there were several reports of horse
poisoning from white snakeroot. These reports have not all
been confirmed, however, recognizing poisonous plants and proper
pasture management are two tools to reduce poisonous plant toxicosis
in the fall.
When an animal goes off feed, loses weight, does not
come up with the herd, or appears unhealthy, poisonous plants
may be the cause. Poisonous plants contain toxic compounds which can
injure, reduce performance or even kill horses. Reductions in
performance include;
exercise intolerance, weight loss, weakness, rapid pulse and
unthriftiness. Poisonous plants should be given consideration
as the potential
cause, especially if the following situations exist:
1. Forage supply in a pasture is sparse due to overgrazing, drought
or poor late season growth
2. Animals have recently been moved into a new pasture
3. Animals have been released into a pasture when hungry
4. Herbicides have been used to control weeds
5. Pasture has recently been fertilized with nitrogen
6. A new forage source has been fed.
Most plant poisonings in pastured animals occur in the early
spring, late fall, or during a drought when feed is short. Plants
that an animal normally would not touch become a potential source
of food and a potential source for poisoning, just because
the animal is hungry and in search of food. Also, some herbicides
may increase the palatability of some weeds, especially
broadleaf weeds. Therefore, it is important to read the herbicide
label and follow all grazing restrictions. If there are poisonous
plants in the pasture, it is best to keep all livestock
out until the plants have died.
This release is focused
on the plants that most commonly cause toxicosis of horses on
pasture in the fall; white snakeroot, maple leaves,
acorns, and hoary alyssum. The plant description,
toxic dose, and clinical signs of toxicity are summarized.
White snakeroot (Eupatorium rugosum) is a perennial plant that
reaches a height of one to three feet tall. Leaves are opposite
with
toothed edges and taper to a pointed end. Flowers are
small and white and generally appear in late August. A 1000 pound
horses eating about 2 pounds of fresh or dried white snakeroot
may develop toxicosis. White snakeroot is poisonous to all
grazing animals during the growing season, when dried in hay,
or when present above the snow in winter. It is found is shaded
areas,
woods, clearings, hardwood pastures and waste places
on moist and fertile soils throughout
Minnesota. Symptoms of poisoning include; depression,
labored breathing, muscle tremors, hanging the head
down, and death. The onset of symptoms is usually noticed 1 to
3 days after
eating.
Red maple (Acer rubrum) is a large native tree
found in moist woodlands and swamps throughout Minnesota. Horse
poisonings have also been associated with other members of the
Acer genus, such as silver maple. Ingestion of 1 to 2 pounds
of dried leaves by a 1000 pound horse is often associated with
toxicosis. Leaves
are opposite, generally triangular with three or five lobes,
coarsely toothed, and silvery white beneath. Poisonings
result from consumption of wilted leaves and has
only been reported for horses.
Toxicity is most prevalent from June through October,
but may be greatest in autumn foliage from dried,
wilted leaves. Symptoms
generally develop one to four days after ingestion
of leaves and include rapid breathing and heart rate,
weakness, depression, jaundice,
cyanosis, brownish discoloration of blood and urine,
coma, and death. Cases
of maple toxicosis in horses are believed to occur
in Minnesota each autumn.
Most species of oaks (Quercus sp) contain toxic phenolic compounds
(tannins). Large quantities of young leaves and sprouts are toxic
when consumed in spring, as are green acorns
when ingested in the fall. Poisoning occurs when
over half the diet is oak buds or acorns, for several days. Symptoms
appear several days
after the period of consumption and include abdominal
pains, weakness, anorexia, colic,
constipation, depression, diarrhea, presence of
blood in urine, jaundice, and death.
Hoary alyssum (Berteroa incana) has been linked to fever and stocking
up, or swelling of the lower legs, in horses ingesting it in hay
or on pasture. Toxic doses for hoaryl alyssum
are difficult to give since about half of dosed horses don't appear
to react adversely to the plant at all. Generally speaking,
hay or pastures consisting of 30% or more of
hoary alyssum should not be fed to horses.
If your horse develops any of these clinical signs, please
call your veterinarian to determine if one of these poisonous
plants is to blame, or if another disease with similar symptoms
is present.
The key to avoiding problems with poisonous plants
is proper identification of the plant, or tree,
and preventing the horses from getting access
to them. Examine pastures, hay fields,
roadsides and fence rows for poisonous plants.
In a drought year, or a year when feed
is short, take extra precautions to look over
new areas planned for grazing or haying such
as roadsides, wooded areas or sloughs. Toxic
plants may be present in new pasture plantings
when the cover crop is not adequate, or in
established plantings after winter kill.
Other management tips to avoid problems include: rotating pastures
to prevent overgrazing, avoid turning hungry animals into new
pastures, fence off areas in pastures where
poisonous plants occur and have
adequate supplies of clean, fresh water for
all grazing livestock.
Visit the Extension
Horse Web site at www.extension.umn.edu/horse for
additional information and pictures of poisonous and noxious
weeds. Information
in the article was obtained from the Extension
Publication Plants Poisonous to Livestock written
by Lisa Axton and Beverly Durgan and an
interview of Dr. Mike Murphy, Toxicologist
at the College of Veterinary Medicine.
Krishona Martinson
Regional Extension Educator, Crops
University of Minnesota Extension
Service
Andover Regional Center
Bunker Hills Activity Center
550 Bunker Lake Blvd NW
Suite L1
Andover, MN 55304-4190
Phone: 763-767-3842 or 888-241-0719
Cell Phone: 612-360-4533
Fax: 763-767-3885
E-mail: bjork026@umn.edu |
