At our general meeting on
November 15th, 2003, Maureen Connor, a weed specialist, was kind enough
to come and give a talk to the members regarding noxious weeds and
how they could be dangerous to our horses. She gave a wonderful talk,
complete with slide presentation and dried weed specimens. She also
gave out calendars and weed identification books to the members to
assist them in identifying and controlling noxious weeds. Here is
a small portion of that information. We hope it will encourage you
to research the topic more and become active in the war on weeds!
Montana State currently
estimates that 8-10% of Montana is infested with noxious weeds.
The losses from livestock eating noxious weeds in 17 western states
was estimated at $107 million dollars, according to the 1978 Journal
of Range Management. So, you can see this is a big problem, one
we all need to be educated about if we are to help control the spread
of noxious weeds and to keep our horses safe and our pastures healthy.
Did you know
that horses can develop picas (addictions)
to toxic plants once they start eating them? In general, most horses
will not seek out weeds to eat if there are other nutritious items
available. However, there is no guarantee that your horse won't
eat one either. Horses in dry lots are particularly vulnerable as
noxious weeds tend to grow in areas like corrals where the ground
has been stressed. A general rule of thumb is, if it's growing in
your corral, it can't be good! This doesn't mean you only find toxic
plants in corrals; they grow wherever conditions are right including
pastures, on mountainsides, near streams, you name it! That means
there could be toxic weeds found in hay, so you should always look
in your hay or the farmground it was cut from to make sure there
are no weeds. And remember, where there are weeds, there are seeds,
which means feeding seed infested hay in a place that didn't have
that weed could spread the weed there!
What do you
do if you find noxious weeds on your property?
Be aware that herbicides can make toxic plants MORE palatable (for
instance, Houndstongue). It is important to contact someone knowledgeable
about weeds and weed control to accurately identify the weed and
determine the best method of controlling that weed in your particular
situation. Your County Extension Agent, County Weed Coordinator,
University, or a commercial weed sprayer can be very helpful sources
of information. There is a Noxious Weed Trust Fund that helps people
with the financial burden of weed control. Access to these funds
is available through local weed management such as the County Weed
Coordinator. It would also be wise to contact your veterinarian
to discuss possible health problems related to toxic plants, and
proper treatment for those problems.
could be harmful to my horse?
that weed poisoning is a tricky subject with no absolutes. Age,
size and general health of horse, type of plant ingested, amount
of plant ingested, time of year/conditions when plant grew before
it was ingested and other factors can all affect how toxic, if at
all, a plant is to your horse. That being said, some weeds that
have possible toxic effects are as follows:
All stages of plant growth may be toxic and could cause permanent
liver damage. If a horse eats 6% Houndstongue of it's daily
intake for 2 weeks, it may accumulate a lethal dose. Prognosis
is death in less than 6 months due to liver failure in that
situation. Houndstongue is easily identified by it's seeds,
which look like teardrop shaped, small burrs. You've probably
found them in your horse's mane or tail, or in your socks
or shoelaces at some point! Do yourself a favor-if you find
Houndstongue seeds stuck somewhere they shouldn't be, don't
pick them off and drop them on the ground. That is how the
weed spreads. Pick them off and throw them in the garbage!
At least landfill sites have the ability to keep such pests
from growing as they have methods to keep anything
from living in a landfill site!
- TANSY RAGWORT:
of a horse's body weight could be a lethal dose. Like Houndstongue,
it also affects the liver. It has been found to maintain it's
toxicity in hay. It can contaminate the milk of grazing animals,
- YELLOW STAR THISTLE:
horses LIKE it. Fortunately, it is not real common in Montana
yet. If ingested it can cause Chewing Disease, where a horse
cannot chew and swallow it's food or water properly. This
condition is incurable and is fatal. The same toxin is found
in Russian Knapweed.
- RUSSIAN KNAPWEED:
Yellow Star Thistle). This too can cause Chewing Disease.
Not to be confused with Spotted Knapweed, which is very common
in Montana. Spotted Knapweed is a noxious weed, but it is
not toxic to horses.
- TALL BUTTERCUP:
toxin in this plant makes horses (and humans!) lips swell
on contact, so it is unlikely (but not impossible) that horses
would eat it. If ingested it could contribute to gastrointestinal
upset, or colic.
- LEAFY SPURGE:
contains latex, which can cause sensitivities in the skin
or eyes-especially on white or light colored horses including
Paints and Appaloosas. Leafy Spurge is common in Montana,
and is extremely difficult to control. Seeds can spring up
to 15 FEET from the mother plant! The tap root is enormous
and can be as deep as the soil is-we're talking a tap root
that can be underground 20 feet with little sprouts all the
way down, just waiting to spring forth a new plant! Herbicides,
flea beatles, sheep and goats are all ways to try and control
it's spread, however it is extremely difficult to control.
- ST. JOHNSWORT:
this is the same thing you find in the alternative medicine
or health food section of stores. AKA Goat Weed or
Klamath Weed, St. Johnswort can cause SERIOUS photosensitivity
in horses who eat it. This condition can become so serious,
a horse's entire skin might slough away from it's body, which
of course is very painful and fatal. It has been said that
there is enough of this plant in Montana alone to fill all
the needs of those who use it for alternative medicine in
the entire world.
cause Nitrate Poisoning in cattle. Kochia is very common,
especially around corrals. It can shift it's response to herbicides
rapidly, so changing your spray every year can help.
- COMMON TANSY:
isn't likely that your horse would eat this as it is very
strong. In fact, some old fashioned remedies called for making
a tea out of this plant. However, it can cause abortion, colic,
cardiac and respiratory suppression, so make sure your horse
doesn't have access to it.
- CANADIAN THISTLE:
not particularly dangerous to horses, this plant can cause
Nitrate Poisoning in cattle, so we thought we'd mention it!
Many horse people also own cows!
- YELLOW TOADFLAX:
cause gastrointestinal upset in horses. It looks like a Snapdragon
with it's pretty yellow flowers.
- WHITE BRYONY:
is a climbing plant. 15 berries are enough to possibly kill
- HOARY ALYSSUM:
cause laminitis and edema (swelling) in limbs.
- COCKLEBURR AND BURDOCK:
These are not
toxic but bear mentioning as the spiny burrs from these plants
have been known to cause corneal ulcers in equines.
These and other weeds could have harmful
effects on your livestock. Symptoms may go unnoticed until it is
too late to save the animal. Horses who have had previous problems
with weed toxicity are more vulnerable to future encounters with
toxic plants, as previous damage could exist that you were unaware
It is important to the well being of
our livestock and our environment to control these noxious weeds
and prevent their spread. The best way to do this is to get involved,
get educated, and be persistant! This is not a short term project,
but something you have to be diligent about year after year. Remember,
the cheapest and safest method of weed control is PREVENTION!
Here are some links to aid
you in researching plants that may be harmful to equines:
Montana War On Weeds
State University Guide To Poisonous Plants
Cooperative Extension: Fact Sheet
of Wisconsin: Weed Science
State Extension Service: Noxious Weeds
Your Local County Extension Agent
Or, you can always utilize a search engine on the internet,
as there is a multitude of information out there!
*Cara Moore and MHJA are not responsible
for typographical errors or misstated information. We encourage you
to utilize your County Extension Service, Veterinarian, County Weed
Coordinator, University, or Commercial Weed Sprayer to obtain complete
and factual information pertaining to this material before making
any decisions regarding weed control or any diagnosis of health problems
you believe may pertain to weed poisoning.