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    Things That Are Toxic To Horses

    Bay horse eating in a field of yellow flowers.

    It can be a challenge to ensure horse residents have healthy, happy lives after coming to a sanctuary, and there are many different aspects of care to consider each day. Unfortunately, toxic and poisonous hazards are sometimes overlooked in the hustle and bustle of operating a sanctuary. While minor exposure to many of these toxins are unlikely to cause serious problems, large amounts can cause severe health issues and sadly, even death. There are also some toxins that are highly dangerous even in small amounts.

    In order to help ensure you never run into this problem, we have compiled this resource of common plants and other potentially toxic things that been known to be a problem for horses.

    Plants That Are Toxic To Horses

    Please see The Open Sanctuary Project’s Global Toxic Plant Database and filter Species Afflicted by equines in order to see a list of plants across the world that are toxic to horses. Please note that, while comprehensive, this list may not contain every single plant toxic to horses!

    Other Potential Horse Toxins

    Cantharidiasis (Blister Beetle Poisoning)

    Blister beetles contain cantharidin, a toxic substance that is used as a defense mechanism against predators. There are more than 200 different species, and they can be found from Mexico to Southern Canada, and from the east coast of the United States as far west as New Mexico. Cantharidin can severely injure or kill horses when even a small amount is ingested. Horses come into contact with cantharidin by ingesting alfalfa hay that has been infested by blister beetles. The oily substance can contaminate the hay even if the beetles were crushed into the feedstuff. Crushing or chemically eradicating the beetles does not diminish the toxin potency.

    Inspecting individual flakes of alfalfa hay before providing them to residents can help reduce the likelihood of poisoning. Dispose of any contaminated flakes, even if you have removed the beetle, as the toxin can still be left behind.  First-cutting hay is less likely to be contaminated than hay harvested later in the year, as the insects likely haven’t yet swarmed by then. Harvest alfalfa before it fully blooms to reduce the chances of beetle contamination. Hay is less likely to be contaminated by crushed beetles when harvested with a self-propelled mower or windrower. Crimping hay crushes the beetles into the hay.

    Horses that ingest a massive amount of toxin may show signs of severe shock, and unfortunately, die within hours. Classic clinical signs are dark, congested mucous membranes, and frequently drinking small amounts of water or submerging the whole muzzle in water and “water playing.” Other progressive signs include colic, depression, anorexia, ulceration of oral mucosa, diarrhea, polyuria (excessive diluted urination) leading to dysuria (difficulty urinating), sweating, delayed capillary refill time, tachycardia (abnormally rapid heart rate), tachypnea (abnormally rapid breathing), muscle rigidity, collapse, dehydration, and synchronous diaphragmatic flutter.

    If you suspect Blister Beetle Poisoning, contact your veterinarian immediately. If early veterinary care is provided, afflicted horses have a chance of recovery.

    Hardware Disease

    Hardware Disease refers to the injuries that can result from any animal resident eating something they shouldn’t, especially pieces of human-made hardware like nails, screws, and staples. Hardware disease can have devastating effects on any resident. Check out our resource on Hardware Disease prevention here.

    Lead Toxicity

    Lead was once used in paints and pesticides, and can also be found from natural environmental sources. Even if you have never used any products containing lead, it may still be present in old barn or fence paint, or in the soil. Places where old machinery and leaded gas have been stored may also have caused contamination, as would old treated lumber and railroad ties. Horses may ingest the lead in the environment through the consumption of grass, clover, and dandelion or from chewing or licking on tainted surfaces.

    Having the soil tested at your sanctuary is an easy way to learn if the environment is safe for residents. You can check with a local environmental conservation service, or agricultural extension office to inquire about testing. It is usually a fairly quick and easy process. Prevent your residents from accessing buildings and fences with old paint, as they may chew or lick these objects and ingest lead.

    Horses with low levels of lead toxicity do not generally exhibit signs. In more serious cases, you may see the following symptoms:

    • loss of appetite
    • weight loss
    • lethargy and weakness
    • incoordination
    • anemia
    • unusual manure consistency or diarrhea
    • respiratory distress or blindness

    Consult a veterinarian immediately if you suspect your horse has ingested lead or is beginning to show symptoms of lead poisoning.


    Mycotoxins are a toxin produced by molds (fungi) that are harmful to many animals. Mycotoxins can affect horses through contaminated food or bedding. Moist, warm environments make a perfect recipe for mold reproduction. The type and amount of mycotoxin a horse digests affects whether the health issues are immediate and short-lived or may become chronic issues. Some  general signs of poisoning include:

    • appetite loss
    • weight loss
    • respiratory issues
    • increased susceptibility to infectious diseases (poor immune function)
    • poor growth rate

    Prevention is key in avoiding serious health issues. Luckily, there are a number of steps you can take to help ensure resident horses do not suffer the ill effects of mycotoxin poisoning:

    • Be sure to keep food, grain, and hay storage areas clean, dry, and cool
    • Try to keep food storage areas protected from mice and rats and other wildlife, as they can chew holes in food bags, increasing the likelihood of grain being exposed to damp conditions
    • Always feed the oldest bags of food first. Try to use up open bags within a few weeks after opening in the winter and in even less time in the summer
    • Clean any storage bins or cans thoroughly to remove old grain that gets stuck in cracks and crevices
    • Check with your food manufacturer or supplier to see if they regularly test for the presence of mycotoxins in grains before mixing food. If they do not, avoid using them and find another supplier
    • Avoid corn screenings (small parts of corn grain that routinely carry very high levels of fumonisins) completely!

    If you are concerned about the possibility of mycotoxin contamination, have your food stores tested. This could be especially important if you have a horse that shows initial signs of mycotoxin exposure.

    Opossum Feces

    Possums are wonderful animals that do a lot for our local ecosystems. Unfortunately, possum feces can carry the protozoan that is responsible for causing equine protozoal myeloencephalitis (EPM). This is a serious neurological disease that affects horses. Ingesting feed contaminated with this protozoan can put a horse at risk of contracting EPM. Sometimes, a possum may get into a food storage area and leave waste behind on hay that horses will eventually eat. Be sure you check hay for waste and dispose of any contaminated hay.

    You can read more about compassionate ways to manage wildlife populations at your sanctuary here!

    Other Animal Food

    While you may think it may be okay to substitute horse food for cow, goat, or bird food for a few days until you can get into town to get more horse food, you would be mistaken. Non-medicated cow, goat, and bird foods are not good for your horses, and medicated feeds can be fatal!

    Medicated food for many other animals at sanctuaries contain Rumensin or Bovatec and other ionophores (antibiotics) to control disease. However, ionophores are EXTREMELY toxic to horses. The safest bet is to only give species-appropriate food to horses, and design you food storage rooms to prevent cross-contamination. Be sure food areas are secure from curious residents that may try to sneak in for a midday snack!

    Horses that have ingested food with ionophores may exhibit restlessness, sweating, incoordination, and colic. Sadly, affected horses often die within 12 to 36 hours after exhibiting symptoms. Horses that ingested a smaller amount may recover but the toxin may cause permanent cardiac damage.  

    Pesticides, Herbicides, And Rodenticides

    It may not come as a surprise that herbicides and rodenticides can cause toxicosis in horses if ingested. If horses ingest plants that have been sprayed with phenoxy acid herbicides, they can become ill or even die. For this reason, it is imperative that horses are not given treated plants or are allowed access to pastures that have been treated with herbicides.

    While rats and mice can pose challenges for sanctuaries, it is important to respect them and use compassionate mitigation practices. Many rodenticides are anticoagulants and act by preventing the blood to clot. These products may be appealing to horses as well, and they may attempt to lick or eat them if discovered. For this reason, it is imperative that they do not come into contact with these poisons. There are many new and innovative ways to address rodent populations that are more effective and compassionate.

    Pesticides may affect the nervous system in horses and can be fatal if not treated with the antidote. Early treatment is critical. If you suspect a horse may have ingested any of the poisons above, contact your veterinarian immediately. Blood tests may confirm poisoning.


    Venomous snakebites are not common, but when they occur, should be treated seriously and immediately. The most common location for a horse to be bitten are on the nose or leg. It is possible for a snake to bite several times, so if you notice a snakebite, look for others. Snake venom varies by species, and the severity of a bite can also be influenced by size, age, and the number of bites. Most venoms can impair blood clotting and damage the heart, while some others contain neurotoxins. Signs of a snakebite may include:

    • Pain
    • Swelling at the bite site
    • One or more puncture wounds
    • Sloughing of tissues near the bite site
    • Cardiac arrhythmias
    • Impaired ability for their blood to clot
    • Shock
    • Collapse
    • Paralysis
    • Death

    Seek veterinary care immediately if a horse is bitten by a venomous snake. Do NOT try to suck the venom out or place a tourniquet. Keep the horse calm while seeking immediate veterinary care. Depending on the severity of the bit, treatments may include antivenin, pain medications, fluid therapy, wound treatment, tetanus vaccination, and antibiotics. Check out our Compassionate Wildlife Practices At Your Animal Sanctuary for some tips on how to dissuade snakes from your property.

    Wood Stains And Paints

    Some wood stains and paints can be toxic to horses. Horses may try to chew on painted surfaces and can become ill if the stain or paint is toxic. Try and purchase paints and stains that are specially made for barns and fencing and listed as animal or “livestock” friendly.

    While this list isn’t exhaustive, it can certainly help you keep resident horses safe, healthy, and happy! 


    Cantharidin Toxicosis From Blister Beetles In Horses | Today’s Veterinary Nurse

    Is There Lead In Your Pasture? | Of Horse

    Animal Friendly Barn And Fence Paint For Horse Stalls | Stuff For Petz

    Plants Toxic To Horses | PennState Extension (Non-Compassionate Source)

    Don’t Give Cattle Feed To Horses! | Kentucky Equine Research (Non-Compassionate Source)

    The Danger Of Mycotoxins | The Horse (Non-Compassionate Source)

    Toxin Topic: Snakebites And Horses | The Horse (Non-Compassionate Source)

    Non-Compassionate Source?

    If a source includes the (Non-Compassionate Source) tag, it means that we do not endorse that particular source’s views about animals, even if some of their insights are valuable from a care perspective. See a more detailed explanation here.

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