Our horses, donkeys, and ponies live in a world full of vegetation. However, in their pastures, on trails, or at the edge of paddocks, hidden dangers often lurk, such as toxic plants and trees that can compromise the health and well-being of our equines.
It is crucial for owners and riders in general to be familiar with potentially deadly plants. In this article, we will describe various toxic plants and trees that may pose a threat, outlining the signs of poisoning, associated risks, and essential preventive measures to protect their health.
Toxic Plants and Trees
Main Toxic Plants
The following non-exhaustive list of toxic plants are the most frequently found and are all deadly. They should be removed from pastures, paddocks, and their surroundings.
Common Yew : the yew often grows to the size of a shrub. Its needles and seeds are highly toxic to equines, among others. The taxines present in yew are cardiotoxic (chemicals that are toxic to the heart, causing muscle alterations or cardiac dysfunction) and can cause severe arrhythmias (abnormalities affecting the normal heart rhythm) if ingested.
Ragwort (Senecio jacobaea) : this plant contains toxins that are not eliminated by the horse’s liver, poisoning it. The lethal dose of ragwort corresponds to 3 to 5% of the horse’s body weight, i.e., 15kg for a 500kg horse.
Foxglove (Digitalis purpurea) : poisoning by this plant is generally caused by contaminated hay. Its toxin causes respiratory paralysis in horses, leading to death.
Rooted Pigweed (Potentilla spp.) : it can be confused with dandelions, leading to mistakes by the horse. Their rosette of leaves has rounded, hairy lobes (small white hairs), distinguishing them from dandelions. If ingested by an equine, it triggers Harper’s syndrome (involuntary hyperflexion of one or both hind limbs).
Highly Toxic Plants for Horses
These plants are not commonly found but must be removed from pastures, paddocks, and their surroundings. If they are present in hay, they must be identified, contaminated bales removed, checked to ensure no other horse has eaten them, and the supplier notified. If a horse ingests even a small amount, the veterinarian should be called immediately.
- Poppy : excitement, nervousness, respiratory issues, cramps, colic, acute gastroenteritis.
- Flax : colic, convulsions, ataxia, motor disorders, death.
- Bracken fern : ataxia, excitement, death.
- Colchicum : abortion in pregnant mares, digestive disorders, respiratory paralysis.
We recommend visually identifying all these plants to recognize them properly and prevent any poisoning of your equines.
Other Plants to Know
To help prevent poisoning, here is a non-exhaustive list of other plants to avoid along with the symptoms they cause if ingested.
Low-toxicity plants for horses : They may cause symptoms in horses, without being an emergency, due to their low toxicity.
- Common Tansy : phases of aggressiveness.
- False Flax : acute gastroenteritis.
- Clover : colic, laminitis, trifoliosis (food poisoning caused by excessive clover consumption in herbivores).
- Laburnum : motor disorders.
- Beech nuts : colic.
Toxic Trees
On trails or even in the pasture, horses may nibble on overhanging tree branches. However, it is important not to let them eat just anything. The following non-exhaustive list presents the main toxic trees for them.
Sycamore Maple : ingestion of its fruits and young shoots causes severe illnesses in horses. It can affect the respiratory system, heart, or postural muscles. Such ingestion is often fatal. Poisonings increase in spring with young shoots and in autumn with falling fruits. Due to the high risk, removal of these trees from areas frequented by horses is recommended.
Black Locust (Robinia pseudoacacia) : when flowering, it produces highly fragrant clusters of white flowers. Its bark is very toxic and ingestion can lead to numerous severe symptoms in horses: digestive disorders, prostration, mydriasis (pupil dilation), cardio-respiratory issues (tachypnea and tachycardia), and high hyperthermia. Beware of horses gnawing on wooden posts, as some may be made from black locust!
Oleander : a tree commonly found in southern France, easily recognizable when in bloom. It is highly toxic, causing death in horses by cardiac arrest, even at very low doses: the lethal dose is 0.005% of the horse’s body weight, i.e., 25g for a 500kg horse.
What to Do in Case of Ingestion
Recognize and React
If you suspect your horse has ingested toxic plants, try to find its name online. If unknown, keep a sample to take to your veterinarian as soon as possible. At the slightest doubt, contact your veterinarian.
Horse digestion can be slow, so side effects or poisoning symptoms may take time to appear. Meanwhile, regularly check your horse’s pulse, breathing, and temperature, and follow your veterinarian’s advice. They will determine whether treatment requires a visit.
The situation becomes urgent if you observe any of the following symptoms:
- excessive salivation
- dry mucous membranes
- skin inflammation (dermatitis)
- pupil dilation (mydriasis)
- tremors
It is important to note that most of these symptoms are not specific to poisoning and can occur for other reasons. Therefore, they should be reported to your veterinarian promptly regardless of the cause.
Preventing Poisoning
Here are some tips to best prevent poisoning:
- If your horse is permanently in a pasture, identify the species present at the start of each season and after any major storm.
- Mow the edges of pastures and paddocks.
- Track toxic plants and remove them from reach over time. For example, move horses before autumn if the pasture is surrounded by oaks.
- Some plants remain toxic after mowing. Learn about their toxicity to know whether complete removal is necessary.
This article does not list all toxic plants and trees. To learn more, the Swiss National Stud Agroscope created a smartphone app called Toxiplant, which lists the seventy most harmful plants for your horses. It provides images of toxic vegetation, characteristic poisoning symptoms, and essential first aid guidance.
