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Plants and Trees Poisonous To Horses


 To Purchase the Book
Horse Owners Field Guide to Toxic Plants
Click below:


To Search Cornell University's
Poisonous Plants Database,

Click here for more information

For a University of Pennsylvania
list of Poisonous Plants, click here:

Click here for more information

For a Purdue University
School Of Veterinary Medicine
list of Poisonous Plants, click here:
Click here for more information

For a printable PDF of
"A Guide To Plants
That Are Poisonous
To Horses and Livestock"


For other helpful links on
plants and trees that are
poisonous to horses,
click on the pictures & links below:

Click here for more information

Colorado State Univ.

Note: When in doubt regarding plantings around your horses, and how safe/unsafe they are, contact your local Cooperative Extension Office and they can help! To locate your closest U.S. Department of Agriculture Cooperative Exension office: CLICK HERE

For poisonous plants in the U.K.:
Click here for more information


Poisonous Plants and Trees
That Can Harm Your Horse
Portions of this below are from an article in the
March, 2001 issue of EQUUS magazine
By Joanne Meszoly

As praiseworthy as trees are, there are a few situations where horses and trees don't mix. In some cases, fruit- or nut-bearing trees contribute to colics when horses gorge on their produce. In others, falling branches or uprooted trees injure nearby horses. But the gravest dangers arise with the few tree species that are toxic enough to sicken or kill horses.

Of the nonornamental native trees, the most deserving of the skull-and-crossbones warning are those that produce cyanide in their wilted leaves. Cyanide suffocates animals by blocking oxygen transport via the red blood cells. The red maple (Acer rubrum) is one such tree whose leaves are harmless most of the year until wind damage or seasonal change causes them to fall from the tree and wilt. Red maple leaves have serrated edges and can turn either red or yellow in the fall. "There are other trees that shed red leaves in the fall, but the red maple has some distinctive features," says Anthony Knight, BVSc, MRCVS, who specializes in toxic trees and plants at Colorado State University. "The underside of the red maple leaf tends to be silvery in color." Signs of poisoning, including lethargy, discolored urine and darkened gums, may not appear for four days.

Equally toxic are cherry (black cherry, chokecherry, and fire cherry) peach and plum trees, all members of the Prunus species. These leaves also produce cyanide when wilted, affecting horses within a few hours of ingestion.

To be safe, remove these deadly trees or relocate horses away from pastures bordered by or containing them. In general, horses are not likely to eat leaves or any other tree parts unless they are quite hungry. However, when curiosity or boredom spurs exploratory bites, the horse may ingest enough of the deadlier species to do harm.

The following trees have no place in horsekeeping areas because of their toxicity or potential for causing digestive distress. They are listed below in order of the risk they pose to horses, starting with the most hazardous. For more information and pictures of many of the below, click on the name:

Some plants and trees that may be present in your pastures or fields could be dangerous or even deadly to your horse. You may see these innocent looking plants every day and not even know that they pose a threat! If you suspect that you may have any of the following around you, you should consult with a vet knowledgeable in toxicology and get them removed before your horse finds them.

First and foremost is the red maple tree. Yes that's right, the common red maple. If ingested, the leaves of the maple contain substances that can cause a breakdown of your horse's red blood cells leading to severe problems. If you have any red maples in your pastures, get them removed immediately and if you don't have them, then definitely don't plant any.

Mountain Laurel is another plant to avoid. Yes for those in PA, our state flower can be toxic to horses.

Rhododendrons and azaleas need to be avoided as well. These 3 plants contain toxins that can cause diarrhea, weakness, impaired vision, and heart problems and can be deadly within 1-2 days.

Milkweed is a toxic plant that we've all seen and chances are your horse may have too. Worse yet, he may think it's a tasty treat. Unfortunately milkweed can cause seizures, lack of coordination and colic in horses and may lead to death 1-3 days after ingestion. One more complicating factor is that milkweed is still toxic after drying so if any of it accidentally winds up in your horse's hay, they could be in big trouble. Please be certain that you know where your hay is coming from.

You may be a bit more familiar with the need to avoid water hemlock as it is quite toxic to humans as well as horses. It is commonly found near streams or in swampy, wetland areas, so be very cautious about letting your horse graze in these regions if you don't know what types of plants are out there. It can cause violent seizures and muscle twitching closely resembling tetanus.

Also causing similar signs is poison hemlock. Poison hemlock can be found in fertile, moist soils in areas such as woodlots, fencerows, and waste areas.

Two other toxic plants found in similar types of environments are sorghum grass and wild cherry trees, which contain cyanide. In PA and other parts of the northeastern and eastern part of the US white snakeroot is apparent. White snakeroot is often found in forest soils or at the interface between forests and croplands. Again the plant is toxic both fresh and dried, so watch out for your hay. Horses can get very depressed or weak if they have eaten this plant, and may show signs similar to congestive heart failure.

Big warning on this next one... black walnut trees. These are very common and shavings or sawdust from these trees sometimes get used as horse bedding. Interestingly, ingestion is not the problem here. Instead, this will likely cause laminitis in your horses hooves. Additionally, some parts of the hoof can become necrotic. If your horse is having problems with laminitis, you may want to inspect your bedding carefully for black walnut shavings. Black locust trees are also particularly toxic to horses and some types of oak trees can be as well, although more so to sheep and cattle. Finally yew, although not commonly grown freely in pastures can be a serious problem if carelessly discarded into a pasture or if animals escape and gets access to landscaped areas.

This is by no means a complete list and I would recommend that any horse owner buy a book containing a comprehensive listing of toxic plants and trees to make sure that your horse doesn't have access to any of them. As I mentioned many of these toxic plants could kill within 1-3 days of being eaten, so avoidance is much better than trying to cure the problem after it happens. As always if you suspect your horse may have eaten a toxic plant or tree, consult your veterinarian immediately. I sincerely hope that this helps to make your horse's life a safe and happy life!


Beware: Acorns Can Cause Colic and Founder

Oaks and their toxicity to horses

Acorns and Stomaches

Acorn Toxicity in Horses

Another link for information on plantings and weeds/grasses that are toxic to horses: CLICK HERE

And here's another excellent article on the subject: CLICK HERE

Note: When in doubt regarding plantings around your horses, and how safe/unsafe they are, contact your local Cooperative Extension Office and they can help! To locate your closest U.S. Department of Agriculture Cooperative Exension office: CLICK HERE



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