Horses are herbivores, which means that their diet is based exclusively on plants and lots of fiber. Most horse owners feed them hay or grain, and some let them graze peacefully on a pasture throughout the day. However, there are plenty of plants out there that are poisonous to horses.
It’s worth noting that horses don’t know how to identify poisonous plants per se. However, most horses will generally avoid toxic plants. They will either dislike their smell and taste or they will just bite off a few leaves by accident and move on. Some of the most dangerous plants for horses include horsenettle, begonia, eucalyptus, ragwort, oleander, seaside daisy, Japanese yew, privet, sycamore, and foxglove.
Today we’re going to have a closer look at each of these plants. We’ll learn how to identify them, what are their main side effects, and what to do if our horses end up eating them somehow.
10. Begonia (Begonia obliqua).
There are more than 1,000 species of Begonia in the wild, and more than 10,000 hybrids. What makes this plant particularly dangerous for horses is that it can cause kidney failure. In cats and dogs, it merely causes vomiting and salivation. That’s not to say it shouldn’t be avoided by these pets, it’s just that it’s less likely to cause any serious damage.
Horses are more vulnerable to the soluble calcium oxalates in begonias than other animals. Since there are so many different types of begonias and so many hybrids, their toxicity levels will vary from region to region. In some parts of the world, people eat these plants because they like their sour taste. Horses are not particularly fond of sourness, so they will likely not ingest a Begonia plant unless they have nothing else to eat.
However, some of these plants might find their way into the horse’s feed by accident. If the ingested quantity produces side effects, you’ll likely have to call your vet and take appropriate measures to nurse your horse back to health.
9. Ragwort (Jacobaea vulgaris).
Ragwort is known for causing problems in pastures. It’s a pesky weed that thrives in wastelands or on pastures that aren’t often grazed. In some parts of the US, the local authorities can legally order landowners to dispose of this weed. It definitely does more harm than good on private property.
The reason why Ragwort is particularly poisonous to animals is that it contains a wide assortment of alkaloids. While these alkaloids don’t deposit in the liver, their byproducts can actually damage a horse’s DNA.
The plant is native to Britain and continental Europe, but fortunately, documented cases of ragwort poisoning are rare. That’s mainly because horses don’t generally ingest the plant due to its bitter taste. If a horse does end up eating enough ragwort, it will usually develop irreversible cirrhosis of the liver. Common symptoms of ragwort poisoning include lack of coordination, depression, and yellow mucus membranes.
8. Horsenettle (Solanum carolinense).
A member of the nightshade family, horsenettle is a perennial herbaceous plant, native to the southeastern United States. For horses, all parts of the plant are poisonous to some degree, but its toxicity levels vary depending on its growing conditions. One of the plant’s natural defenses comes in the form of solanine glycoalkaloid which is a toxic alkaloid.
Horses that eat horsenettle in large quantities will develop clear symptoms, including diarrhea, dilated pupils, and confusion. They might also experience loss of appetite and general weakness. In some rare cases, horsenettle will prove deadly to horses, but only if the horse has eaten more than two pounds of the plant.
I wrote an entire article about Horse Nettle and its toxicity to horses. In it, you can learn how to identify this plant, how to remove it from your property, and how to tell if your horse has eaten it to a dangerous degree. Make sure to check it out if you’d like to learn more about this plant.
Are Eucalyptus leaves poisonous for horses? There’s no debate about it: eucalyptus is harmful to equines, but only if ingested in large quantities. This seems to be a trend for many toxic plants, although there are a few of them that can cause death from a single mouthful.
Eucalyptus is not one of these plants, but the chemicals that it contains can cause contact dermatitis. Moreover, the leaves also contain cardiac glycogen, which increases blood pressure by making the heart pump harder. Most Eucalyptus plants are native to Australia, so if you and your horse live in the United States, the chance of poisoning is definitely lower.
Horses will generally avoid Eucalyptus if they have something else to munch on. The problem is that horses kept in paddocks or stables for extended periods might just choose to the nearest plant available, and in large quantities, even if that plant proves to be toxic.
To horses with heart conditions, Eucalyptus can do some serious damage. To healthy horses who just happen to bite off a few leaves once or twice, it will be largely harmless. It still contains damaging toxins, though, which is why I had to include it in this list. Bottom line, don’t allow your horse to eat Eucalyptus, just to be on the safe side.
6. Privet (Ligustrum vulgare).
Privet is an evergreen shrub that’s part of the olive family. Usually, you’ll find this shrub in near proximity to fences or hedgerows, and even on abandoned farmlands. It can grow up to 15 feet tall, and it has dark blue berries as well as small white flowers. Horses generally avoid eating privet because it gives off an unpleasant odor when they bite into it.
Privet is also a very common ornamental hedge. Its berries and leaves are poisonous to horses, but the good news is that they mostly cause gastrointestinal issues. There are some cases in which horses have developed much more serious conditions, though. These include paralysis and convulsions, as the toxins can also affect an equine’s nervous system. In some cases, horses have died from eating privet.
It’s worth keeping in mind that the privet berries have the highest concentration of glycosides. While there’s no specific cure to treat privet poisoning in horses, fluid and electrolyte therapy can help ease symptoms and bring the horse back to its feet.
If you suspect that your hay and feed supply might contain privet mixes or any other plants that might be harmful to your horse, be sure to check it regularly or even switch suppliers altogether.
5. Sycamore (Acer pseudoplatanus).
Sycamore is a large deciduous, broad-leaved tree that can grow up to 115 feet tall. Its seeds can spread up to 3 times the height of the parent tree, and even further during severe weather conditions. Sycamore poisoning in horses is extremely serious, and it accounts for a large number of deaths every year.
That’s because horses ingesting seeds or emergent seedlings from a Sycamore tree will develop a fatal condition named atypical myopathy. This disease targets the horse’s muscles, particularly those that enable it to stand up and breathe. Moreover, since the heart is also a muscle, the condition could affect it as well.
Horses that suffer from sycamore poisoning will generally look lethargic, will have a hard time working, and they might become very stiff and trembly. As the disease progresses, the horse will suddenly collapse and die, unless it receives treatment shortly after poisoning. It’s worth noting that even with treatment, some horses will die of atypical myopathy anyway.
As for the plant’s toxicity levels, it’s been reported that only a few dozen seeds or seedlings are enough to cause the disease.
4. Seaside daisy (Erigeron glaucus).
Who knew that something as cute as a daisy could prove life-threatening for your horse? The Seaside daisy is particularly nasty for horses, as it can cause severe disturbances in the animal’s digestive system. Also known as Erigeron glaucus, this daisy is native to the pacific coastal areas of the United States. It thrives in sandy soil and beaches, so if your property is near a beach or a spot of sand on the Pacific coast, you might want to check it for daisies.
This perennial can grow up to 3 feet tall, and it has branching stems. The flowers have yellow cores flanked by purple, blue, or white petals. The Seaside daisy is not particularly difficult to spot if you know what to look for.
If your horse comes in contact with it, the Seaside daisy can cause rashes, hives, and scabs. If ingested, the plant causes a particularly bad type of diarrhea, which can be life-threatening if not treated promptly. Therefore, there are two types of Seaside daisy poisoning in horses: the one that comes in contact with the skin, and the one that results from ingestion.
When treating Seaside daisy skin disorders, the vet might opt to use certain shampoos or sprays that will diminish inflammation and itchiness. If ingested, treatment will consist of fluid and electrolyte therapy complemented by protein supplements and other medication intended to rejuvenate the horse’s intestinal flora.
3. Foxgloves (Digitalis).
As beautiful as they may be, Foxgloves are incredibly dangerous and toxic for horses. Depending on its species Foxgloves may contain numerous deadly physiological and chemically related cardiac and steroidal glycosides. For this reason, this plant is commonly known as dead man’s bells in some parts of the world.
The chemicals in Foxgloves affect the heart, especially digitoxin. This is actually used in certain heart medications, and in controlled doses, it can do plenty of good. Take too much of it, though, and you get fatal arrhythmias.
If horses ingest as little as a few hundred grams or 7 ounces of these flowers, they will likely experience serious side effects, some of which might prove deadly. These include staggering, collapse, depression, and bloody diarrhea.
To treat Foxglove poisoning in horses, the vet will likely use a combination of activated charcoal, oral liquid paraffin, and fluids in order to reduce the absorption of the toxin.
Foxgloves are common on horse pastures. They have beautiful bell-shaped” flowers, and they are known to grow quite tall. If you see any on your own property, you might want to relocate them so your horses won’t eat them by accident.
2. Japanese yew (Taxus cuspidata).
Sometimes, the Japanese yew is planted on purpose as a decorative shrub. In the wild, it grows in both shaded and sunny areas, in well-drained soil with access to consistent moisture. When ingested, Japanese yew is one of the most toxic plants for horses, as even a very small quantity can prove fatal.
To be more specific, if a horse eats as little as 0.1 percent of its body weight in Japanese yew leaves, it has a very good chance to die. There is no antidote for yew poisoning at the time of writing, but atropine is widely used to treat its symptoms. The toxic elements remain within the plant all-year-long, with maximum levels being achieved in winter. Even if dried, Japanese yew is still toxic.
In order to identify this plant, look carefully for its needles, which are light to yellow-green in spring and dark green in the later seasons. The yew can grow as tall as 50 feet, and it has a very fine texture.
1. Oleander (Nerium).
You’ll find Oleander most commonly in the Southern parts of the United States. It is a common ornamental plant that’s kept both outdoors and indoors. It’s also arguably the most poisonous plant for horses. Upon ingestion of Oleander, humans and livestock will experience disturbances in their gastrointestinal system, heart, and central nervous system.
In horses, Oleander is known as a primary source of colic. Its main toxin is oleandrin, which causes heart arrhythmias that lead to cardiac arrest and death. All parts of the plant are toxic for horses, but the leaves are particularly dangerous. As little as 1 ounce of green leaves can be lethal to a horse.
Horses typically die 8 to 10 hours after consuming a deadly dose of Oleander. The problem is that symptoms rarely last more than 24 hours before death occurs, and sometimes they are difficult to spot. Some of the more common symptoms of Nerium poisoning include colic, muscle tremors, diarrhea, ataxia, and difficulty breathing.
Horses won’t eat the leaves in most cases simply because they don’t like the taste at all. However, dried up Oleander leaves retain their toxicity, and they can end up in a horse’s feed, or on a pasture between tall blades of grass.
What To Do if Your Horse Has Eaten a Poisonous Plant.
While it’s always advised to feed your horse high-quality hay and grain sourced from reputable suppliers, it might still end up eating something toxic throughout its lifetime. Even the most careful of horse owners are sometimes faced with a difficult prospect: their horse has eaten a poisonous plant of some kind. What can they do about it?
- Call your vet. If you suspect that your horse has ingested a toxic plant, it’s important to call your vet as soon as possible and have him or her perform a series of tests in order to determine the correct treatment course. If you can help by identifying any potential “plant suspects” all the better.
- Identify the plant. Look for poisonous plants on your property, particularly those that grow where your horse grazes throughout the day. Look for half-eaten plants, broken branches, or any berries. Use the information I provided above to identify the plant and inform your vet of its presence.
- Don’t panic. While some plants are able to put down a horse in a few days or even a few hours, most toxic plants will cause gastrointestinal issues, which are not fatal. Keep calm around your horse and reassure him as much as you can. It’s going through a painful and difficult time, but it can still pick up on your emotions.
- Remove the plants. As your horse recovers from eating a toxic plant, it’s your responsibility to remove the plant from your property. Decide whether you want to use a chemical or a mechanical solution for this, and get to work removing those plants from your horse’s reach.