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Plants Poisonous to Horses November 23, 2009 7:51 AM

Plants Toxic to Horses - Deadly Nightshade


Deadly nightshade likes sandy soil and thrives even in dry conditions. I've become very familiar with this plant's vining habits on my own property. It has a white star shaped flower and the fruit looks like a large black current. All parts of this plant are toxic to humans and pets.


The leaves are dark green and smooth textured somewhat similar to that of a tomato plant. (It is in the same family as tomato, potato and pepper plants which is why you don't want your neighbor pitching his garden scraps over your fence.) Nightshades can be difficult to eradicate.


Horses are unlikely to eat nightshade or any other toxic plant unless there is no other feed available or it is baled into the hay and eaten accidentally. Signs of nightshade poisoning may include:


  • colic like symptoms
  • loss of muscle control
  • disorientation
  • dilated pupils
  • death


Also known as Eastern Black Nightshade.


Resource: Ontario Ministry of Agriculture and Rural Affairs, Poisoning of Horses by Plants, Penny Lawlis - Animal Care Inspector/OMAFRA.


If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:52 AM

Plants Toxic to Horses - Buttercups


I photographed these buttercups on the margin of a marshy area in a pasture. The flowers are yellow and cup shaped with sharply lobed leaves off of a thin stem. The grass around them was well grazed. Horses will avoid eating buttercups if there is more desirable feed available. After a hard frost or dried in hay buttercups are no longer toxic.


Buttercups may cause:


  • irritation of the mouth area
  • colic like symptoms
  • diarrhea


Resource: Indiana Plants Poisonous to Livestock and Pets Cooperative Extension Service, Purdue University


If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:53 AM

Plants Toxic to Horses - Bracken Fern


Bracken fern is very common, growing along roadsides, in fields, in light bush areas and even gardens. In the spring 'fiddleheads' unfurl into triangular fronds up to 3ft (1m) high. I've had horses snatch a mouthful of fern while riding and they seem to find it palatable. Bracken fern dried and baled into hay is still toxic. If a horse eats a large quantity of this fern the toxins can cause a Vitamin B1 deficiency.


Symptoms of bracken fern poisoning may include:


  • loss of coordination
  • depressed heart rate
  • arrhythmia
  • weight loss
  • eventual death if not promptly treated


If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:54 AM

Plants Toxic to Horses- Horse Tails


The soil around my old property is largely sand and gravel. It drains quickly, making it the perfect for this variety of horsetail. Other varieties grow in more marshy areas. If the plant is dried into hay the toxin may have a greater effect than in the fresh plant. The toxin in this plant destroys the Vitamin B in the horse's blood.

Symptoms of Horsetail poisoning are:


  • weakness
  • stumbling
  • arrhythmia of increased pulse
  • death
  • irritability

If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:55 AM

Plants Toxic to Horses - Lamb's Quarters


In some areas this plant is called pigweed or lamb's quarters. The plant I've photographed here is what we call lamb's quarters. It has smooth, light colored leaves and a woody red stem. The 'flower' looks rather like small pale green cauliflower cluster.


A horse would have to eat a large quantity of lamb's quarters for the toxin to take effect. Unless there is no other feed available it is unlikely a horse will eat this plant.

If a horse consumes a large quantity of lamb's quarters symptoms may include:


  • weakness
  • lack coordination
  • respiratory distress
  • coma
  • kidney failure


Resources: Indiana Plants Poisonous to Livestock and Pets Cooperative Extension Service, Purdue University


If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:56 AM

Plants Toxic to Horses - Lily of the Valley


This common garden plant is toxic to humans and pets, including horses. Lily of the Valley is unlikely to be growing in a pasture. It could be accidentally ingested if someone were to throw garden clippings close to a fence line where curious horses might be able to reach. Garden and lawn clippings should be disposed of out of reach of horses.


If you suspect poisoning from any plant or substance call your veterinarian immediately.


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 November 23, 2009 7:57 AM

Plants Toxic to Horses - Milkweed


Milkweed is a very common pasture plant. Elliptical shaped leave branch off of a central stem. When any part of the plant is torn it will ooze a white, sticky sap. The flowers grow in a ball shaped cluster and when in full bloom are a lavender color. The pods develop to about 3" and in fall split open to release brown seeds that float through the air on downy fibers. All parts of the plant are toxic. Living and dried plants (accidentally baled into hay) are toxic. Like most toxic plants horses will avoid milkweed unless they have no other food source. Signs of milkweed poisoning are:


  • disorientation
  • loss of muscular control
  • spasming
  • rapid and weak pulse
  • respiratory paralysis

Milk weed poisoning is rarely fatal.


Resource: Ohio State University, Bulletin 762-00: Horse Nutrition, Poisonous Plants


If you suspect poisoning from any plant or substance call your veterinarian immediately.



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 November 23, 2009 7:57 AM

Plants Toxic to Horses - Pigweed


Pigweed can be very toxic if eaten in large quantities. Horses are unlikely to eat this plant unless there is no other food available. This weed seems to grow everywhere--from pastures to vegetable gardens, roadsides to barnyards. It is still toxic if dried and baled into hay. Pigweed, and its relative lamb's quarters can cause kidney failure. Other symptoms of pigweed ingestion may include:


  • respiratory distress
  • weakness
  • lack of coordination
  • coma

Resources: Indiana Plants Poisonous to Livestock and Pets Cooperative Extension Service, Purdue University


If you suspect poisoning from any plant or substance call your veterinarian immediately.



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 November 23, 2009 7:59 AM


Plants Toxic to Horses - Red Maple


I love the red maples on our property for their brilliant fall color. But I am glad that these trees are situated too far away for curious ponies to get at them.


The bark of red maples is smooth and grayish. The twigs are reddish brown.


The fresh leaves are considered relatively safe, but wilted and fallen leaves can be toxic--but tasty, to horses. The toxins affect the red blood cells. Three pounds of ingested red maple leaves is considered lethal.


Leaves can remain toxic for several weeks after they've fallen. Don't dispose of red maple leaves in manure piles or compost heaps that might be in reach of your horses. Red maple leaves can cause problems if baled into hay.


Red maples grow throughout eastern United States and Canada.

Symptoms of red maple poisoning are:


  • dark brown urine
  • rapid pulse
  • increased respiration
  • coma

Resource: Indiana Plants Poisonous to Livestock and Pets, Cooperative Extension Service, Purdue University Rebecca J. Goetz, writer, extension assistant Thomas N. Jordan, extension weed scientist John W. McCain, extension weed scientist Nancy Y. Su, assistant


If you suspect poisoning from any plant or substance call your veterinarian immediately.



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 November 23, 2009 8:00 AM

Plants Toxic to Horses - Red Oak


Before we bought our former property I very nearly passed it over because of the three large red oaks behind the house. The leaves of red oaks are toxic to horses. Thankfully they are far enough away from the paddocks that the horses can not reach them.


While I've had my horses snatch a mouthful of oak leaves while riding with no apparent harm, a large quantity can be dangerous.


Various varieties of oaks live throughout North America. Horses will eat the leaves if there is no other food available. Water may be contaminated by fallen leaves. Acorns are also toxic if eaten in quantity.


Signs of oak poisoning are:


  • colic symptoms
  • diarrhea
  • darkened urine
  • depression


Resource: The Ohio State University Extension: Horse Nutrition Bulletin 762-00 - Trees and Shrubs


If you suspect poisoning from any plant or substance call your veterinarian immediately.



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 November 23, 2009 8:02 AM

Plants Toxic to Horses and Ponies - St. John's Wort


When I first moved to former home I noticed the lovely field of yellow flowers next door. From mid-July to mid-August St. John's Wort blooms in our dry sandy soil. If you crush the flowers between your fingers, it will leave a rusty reddish stain. Some people soak the flowers in a vegetable oil base to make what is believed to be a healing oil. I found out the hard way that it is not a good way to treat a sunburn on a horse's nose--it actually makes it worse. St. John's Wort causes photo sensitivity--whether it is ingested or as an oil applied to the skin.


If you suspect poisoning from any plant or substance call your veterinarian immediately.



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List of above plants... November 23, 2009 8:05 AM


St. John's Wort

Red Oak

Red Maple



Lily of the Valley

Lamb's Quarters (or Pigweed)

Horse Tails

Bracken Fern


Deadly Nightshade


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 November 23, 2009 8:06 AM


If you know of others please post them (with a photo would be helpful).



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 November 23, 2009 8:08 AM

Another list compiled by ASPCA...


Toxic to Horses

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More... November 23, 2009 8:10 AM

Next  [ send green star]
 November 23, 2009 11:03 AM

Thanks Katii!!! Here is another list:


  • Acorns
  • Alder Buckthorn
  • Black Bryony
  • Black Nightshade
  • Box
  • Bracken
  • Broom
  • Buckthorn
  • Buttercup
  • Celandine - Greater
  • Charlock
  • Cherry Laurel
  • Chickweed
  • Clover
  • Columbine
  • Corncrockle
  • Cowbane
  • Cuckoo Pint
  • Darnel
  • Deadly Nightshade
  • Foxglove
  • Ground Ivy
  • Groundsel
  • Hellebore
  • Hemlock
  • Hemlock Water-Dropwort
  • Hemp Nettle
  • Henbane
  • Herb Paris
  • Horse Radish
  • Horsetail
  • Iris
  • Laburnum
  • Larkspur
  • Lily of the Valley
  • Linseed
  • Lupin
  • Marsh Marigold
  • Meadow Saffron
  • Melilot
  • Mercury
  • Monk's Hood
  • Oak
  • Pimpernel
  • Poppy
  • Potato
  • Privet
  • Ragwort
  • Rhubarb
  • Rododendron
  • Rush
  • St Johns Wort
  • Sorrel
  • Spurge
  • Thorn Apple
  • White Bryony
  • Woody Nightshade
  • Yew



There are others not on these lists, like oleander for example. Some are very serious risks and some aren't, so don't panic if you have some of them on your pasture. If in doubt ask a vet. As I said before, it also depends on your horse. Katie is guaranteed never to eat anything bad. Others are not so picky!!

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Watch for Poisonous Weeds in Hay November 23, 2009 12:16 PM


Most weeds are not palatable and will be avoided by pastured livestock if adequate forage is available. However, in hay, most livestock cannot differentiate weeds from beneficial long-stemmed forage, which can result in accidental ingestion and possibly a loss in performance or even death.


Three weeds commonly found in the upper Midwest that remain toxic when dried in hay are hoary alyssum, wild parsnip, and poison hemlock.


Hoary alyssum is toxic only to horses. It's a perennial weed that is commonly found in pastures and hay fields after areas experience drought. Hoary alyssum is light green to gray in color with white flowers. The seeds are small and oblong and easily seen in baled hay. Horses that ingest hoary alyssum might experience stocking-up or swelling of the limbs, founder, and even death. The toxic dose of hoary alyssum is estimated at 20% (of the plant ingested) in hay, but is known to affect some horses differently. Some horses have a zero tolerance to hoary alyssum.


Wild parsnip is a biennial that is toxic to cattle, horses, and sheep and is infesting ditches and fields in Minnesota. Leaves are course, with saw-toothed edges. Flowers are yellow, and umbrella-shaped. Wild parsnip can contain a toxin called furanocoumarins and can create severe skin irritations. High levels of the toxin have been found in all parts of the plant, including the seeds. The toxic dose of wild parsnip is not known. Signs and effects of toxicity include severe sunburn (photosensitivity). If you suspect wild parsnip toxicity, remove the plant source. Move all affected animals to a shaded area. A topical treatment can be applied to skin lesions. Since wild parsnip is commonly found in ditches, hay harvested from ditches containing wild parsnip should not be fed to livestock.


Poison hemlock is found in wet sites or along streams. Poison hemlock is a biennial that produces a rosette of leaves near the ground in the first year of growth, followed by an erect, flowering stalk the second year. Leaves have a lacy appearance and smell like parsnip when crushed. Flowers are white and are borne in umbrella shaped clusters. The tap root resembles a small white carrot. Poison hemlock contains alkaloids that are toxic to cattle and horses when 0.5% and 0.25% respectively of body weight are ingested. Clinical signs include death, salivation, and excitement. Treatment is rarely possible.


Remember to work with a veterinarian if you suspect a plant poisoning. Several clinical signs associated with plant toxicity can also be associated with other severe and deadly disorders. Evidence of poisonous plant ingestion, clinical signs, and diagnostic tests should be used to confirm poisoning from a toxic plant.


More information and photos of toxic plants.



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 November 23, 2009 12:17 PM

Lynn, I'll bet the others are listed at the pages those numbered links go to.



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 November 23, 2009 1:13 PM

Watch for Poisonous Weeds in Hay..........absoilutely, Katii. That is why it is very important to have a good reliable source of hay. Bad hay can cause all sorts of problems apart from poisoning!
But back to the poison plant thing, ragweed or ragwort will be rarely ingested in its growing state because of it's unpleasant taste so most cases of poisoning is from the plant found in hay in its dry state, because it is more palatable when dried. A horse needs to eat about a kilo of it to do any harm. But if you are feeding bad hay and the horse is hungry.....................................
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 November 24, 2009 8:41 AM

Maybe I missed it in the lists, but one we have here is Datura, also known as Jimsonweed.  Beautiful trumpet shaped flowers in shades of cream and lavender.  Horses can become addicted to it if they develop a taste for it.  It is toxic and hallucinogenic.  I remember reading some years ago that some kids in Fla. became very ill experimentig with it.


Re: poison weeds in hay - we recently had a very unfortunate expeerience at the rescue ranch. Two of the cows, both Herefords, became very ill and eventually died, dispite anything the vet could do.  The post-mortum showed liver failure due of some type of toxin, but couldn't be specific.  All we could figure is that there was something in the hay, probably just one flake, that those two shared.  The strange thing was that out of a herd of 16, mixed breeds, those two were the only ones affected.

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 November 24, 2009 11:52 AM

Good info, thanks! Thinking about it, I've rarely seen a horses eat leaves. Too, I know we have lots of oaks & maples in the area and have never heard of a problem.


I'm going to hazard a guess that oak & maple leaves, on a whole, just aren't very appetizing to horses. If they ate them, I'm guessing they'd have to be pretty damn hungry & desperate. I'm going to guess, too, that they'd have to consume a helluva lot for toxic levels.


That's one of the reasons I like having lots of quality pasture! Horses with plenty of good grass usually don't look for alternatives.  

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 November 24, 2009 1:20 PM sorry about the cows!

Barb, in my experience you are right. If horses have enough good stuff to eat, they don't eat sh*t, except for a TB mare I had who would have eaten old socks if they were lying around!! For example, I know someone whose horse got poisoned from eating buttercups because they were on bad pasture with no hay given to them and were just starving.


Good pasture isn't an option here, so providing good quality hay year round is the only is probably a bit more expensive!

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