Poisonous plants for horses:
which plants are dangerous and how can you identify them?

Poisonous plants for horses: which plants are dangerous and how can you identify them?

As pastures become more bare after summer and horses are fed more hay during autumn, it is especially important to be aware of poisonous plants. Some plants are not only dangerous when eaten fresh but also retain their toxic properties after drying. In addition, acorns, leaves and seeds from trees can end up in horse pastures during autumn.

But which plants are poisonous to horses? How can you recognise the risks, and what can you do to prevent your horse from eating toxic plants? We’ve outlined the most important things you need to know.

Which plants and trees are poisonous to horses?

Not all plants growing in and around horse pastures are safe for horses. Some contain substances that can be harmful if ingested. The severity of poisoning depends on several factors, including the type of plant, the amount consumed and the circumstances.

Here are some well-known poisonous plants and trees that horse owners should be aware of:

• Ragwort: Contains pyrrolizidine alkaloids, which are harmful to the liver. This plant remains toxic even when dried in hay.
• Acorns and oak leaves: Contain tannins that can be harmful when consumed in large quantities, particularly to the kidneys and gastrointestinal tract.
• Sycamore seeds and young seedlings: The sycamore maple (Acer pseudoplatanus) poses a particular risk. It contains hypoglycin A, a substance that can cause atypical myopathy.
• Yew: An extremely poisonous plant that can cause serious health problems even when relatively small amounts are consumed.
• Boxwood: Contains toxic alkaloids that can cause health problems if ingested.
• Foxglove: Contains substances that can affect heart function.
• Horsetail: Some species of horsetail contain substances that can cause health problems when consumed over a prolonged period, including vitamin B1 deficiency.
• Water hemlock: A highly poisonous plant commonly found in wet areas and along waterways.

Regularly check which plants are growing in and around your horse’s pasture. Don’t forget to inspect the vegetation on the other side of the fence as well. Horses can sometimes reach further than you might think!

Why is ragwort in hay so dangerous for horses?

Ragwort is one of the best-known poisonous plants for horses. It contains pyrrolizidine alkaloids, substances that can be converted into harmful compounds in the body after ingestion, causing liver damage.

What makes ragwort particularly dangerous is that the effects are not always immediately visible. Repeated consumption can gradually damage the liver, even when your horse initially shows few or no symptoms.

Ragwort poses a particular risk when present in hay. Horses often avoid fresh ragwort because of its unpleasant taste, but this taste becomes less noticeable during drying. However, the toxic substances remain present, meaning horses may unknowingly consume ragwort through their forage.

That’s why it’s important to check not only your horse’s pasture but also the hay you feed. Look out for unwanted plants and preferably choose forage from a known and reliable source. If you suspect a batch of hay contains ragwort, do not feed it to your horse and have the hay assessed.

Which poisonous plants and trees pose the greatest risk in autumn?

Autumn brings specific risks for horses. As grass becomes shorter and trees begin shedding their leaves and seeds, horses may come into contact with poisonous plants and plant material that would normally be out of reach.

Acorns and oak leaves

Acorns and oak leaves contain tannins. These substances can be harmful, especially when horses consume large quantities. Sensitivity varies between horses, and tannin levels can also differ.

Are there oak trees in or directly next to your horse’s pasture? Regularly check how many acorns and leaves have fallen onto the ground. Ideally, fence off areas where large quantities of acorns have accumulated.

Sycamore seeds and atypical myopathy

The sycamore maple poses a particular risk during autumn because of its winged seeds, often called helicopter seeds. These seeds may contain hypoglycin A, a substance associated with atypical myopathy. Atypical myopathy is a serious condition that disrupts energy metabolism in the muscles. Young sycamore seedlings can also pose a risk, particularly during spring.

Not all maple species carry the same level of risk. That’s why it’s important to identify which trees are growing around your horse’s pasture.

Poisonous garden cuttings

Plants that naturally grow in pastures aren’t the only potential danger. Garden waste and cuttings from plants such as yew, boxwood and other poisonous garden shrubs can also pose a risk.

Never dispose of garden cuttings in a horse pasture. Make sure branches and leaves from neighbouring gardens cannot fall or be placed within your horse’s reach.

How can you recognise signs of poisoning in horses?

The symptoms of plant poisoning in horses can vary considerably depending on the plant involved and the amount consumed. Some toxic substances cause symptoms quickly, while others may only produce noticeable effects after a longer period.

Possible warning signs include:

• Lethargy: Your horse seems unusually tired, responds differently than normal or isolates itself from other horses.
• Changes in droppings: These may include diarrhoea or unusual manure production.
• Excessive salivation: Your horse drools more than usual or shows abnormal chewing behaviour.
• Unsteadiness or muscle problems: Your horse moves in an uncoordinated way, stumbles or has difficulty walking.
• Signs of colic: These may include abdominal pain, restlessness, looking at the abdomen or rolling.
• Changes in appetite: Your horse suddenly eats less or refuses feed.

These symptoms can also have other causes. In addition, not every case of poisoning produces obvious symptoms immediately.

Do you suspect your horse has eaten a poisonous plant? Contact your veterinarian immediately, even if your horse is not showing any symptoms yet. Remove the suspected toxic plant from your horse’s reach and, if possible, keep a sample or take a photograph to help identify the plant.

How can you prevent your horse from eating poisonous plants?

Prevention is always better than cure. Fortunately, there are several simple steps you can take to reduce the risk of your horse consuming poisonous plants.

1. Regularly inspect your horse’s pasture. Identify which plants are growing and pay particular attention to seasonal changes.
2. Prevent overgrazing. When little grass is available, horses may be more likely to eat other plants. Make sure your horse has access to sufficient suitable forage.
3. Check your hay. Look out for unwanted plants and pay close attention to the quality and origin of your forage.
4. Pay attention to trees surrounding the pasture. Especially during autumn, check for fallen acorns, leaves and sycamore seeds.
5. Remove poisonous plants safely. Make sure horses cannot access uprooted plants or garden cuttings. Some plants remain toxic even after they have been removed or dried.

By regularly checking your horse’s surroundings, you can significantly reduce many of these risks.

A safe horse pasture starts with good knowledge

Poisonous plants are not always easy to recognise, and some species remain dangerous even after drying. By regularly inspecting your horse’s pasture, carefully checking the quality of forage and being aware of seasonal risks, you can help reduce the likelihood of plant poisoning.

Not sure whether a particular plant is safe for your horse? Always identify the plant before allowing it to remain in the pasture or offering it to your horse. And if you suspect your horse has eaten something poisonous, always contact your veterinarian immediately.