Find out the Poisonous Plants for Horses in Australia

Part 1 of our 2 part series on Poisonous Plants for Horses

Poisonous Plants and Toxic Substances – A Guide for Horse Owners

What are the poisonous plants for horses?

Certain plants and substances are toxic to horses and pose serious health risks if ingested or touched. Some can even kill and quite quickly if not treated promptly.

Although horses are generally quite astute about avoiding toxic plants, possibly because many of them don’t taste very nice, they will eat certain ones.

Knowing what plants are toxic to horses in your particular area, and ensuring your paddocks are clear of them, is therefore important.

Poisonous Plants for Horses in Australia

Well-known plants in Australia that can be toxic to horses include…

Yew

The evergreen yew tree and its various parts, such as needles and bark, contain highly toxic alkaloids that can be fatal to horses.

Red Maple

Consumption of wilted or dried leaves from the red maple tree can lead to red blood cell damage and kidney failure in horses.

Paterson’s curse

Also known as Salvation Jane, this plant is toxic to horses when consumed in large quantities. It contains pyrrolizidine alkaloids that can cause liver damage and other complications. It can also lead to photosensitivity and skin inflammation.

Arum lilies

These are also known as calla lilies, these attractive white flowered plants are nevertheless toxic to horses due to the presence of calcium oxalate crystals in their leaves and stems. When horses ingest these plants, the crystals can cause irritation and inflammation in their mouths, throat, and digestive system. This can lead to symptoms such as drooling, mouth ulcers, difficulty swallowing, and colic. In severe cases, it can even result in kidney damage or failure.

Ragwort

This weed is toxic to horses both when fresh and when dried in hay. It contains hepatotoxic pyrrolizidine alkaloids, which can lead to irreversible liver damage and even death.

St. John’s Wort

This plant contains phototoxic compounds called hypericin and hyperforin. When horses consume St. John’s Wort and then get exposed to sunlight, it causes burns and severe photosensitivity.

Lantana is a well known poisonous plant for horses

Lantana contains toxic compounds called triterpenoids and alkaloids. Consuming this plant can cause liver damage, gastrointestinal issues, and muscle weakness in horses.

Onion Grass or Onion Weed

Onion Grass, also known as Guildford Grass, produces compounds known as n-propyl disulfide and n-butyl disulfide, which damage red blood cells and can lead to haemolytic anaemia in horses. Symptoms may include weakness, abdominal pain, and pale mucous membranes.

Avocado trees

Avocado leaves and fruit contain a substance called persin, which is toxic to horses. It can cause heart and lung congestion, oedema, and colic.

Oleander is a poisonous plant

All parts of the oleander plant, including leaves, flowers, and stems, contain toxins called cardiac glycosides. Ingestion can lead to severe gastrointestinal upset, difficulty breathing, and even heart failure.

Deadly nightshade

The deadly nightshade plant is highly toxic to horses. Its berries contain an alkaloid called atropine, which can cause severe colic, drowsiness, difficulty breathing, and potentially even death.

Cape tulip

The bulbs of the cape tulip plant are poisonous to horses. Ingestion can cause severe liver damage, leading to jaundice, weight loss, and potentially death.

Box hedge

All parts of the box hedge plant, especially the leaves, are highly toxic to horses. They contain alkaloids that can cause severe gastrointestinal upset, colic, and potentially even death.

Bracken fern

While not immediately toxic, prolonged consumption of bracken fern can cause thiamine deficiency in horses, which can result in neurological disorders such as staggering, tremors, and weakness.

Sweet pea

Sweet pea plants, including the seeds, flowers, and pods, contain amino acid toxins that can cause irreversible neurological damage in horses if ingested regularly. Symptoms include weakness, loss of coordination, and paralysis.

Yellow burr weed

This plant contains pyrrolizidine alkaloids that can damage the liver of horses if consumed in large quantities over an extended period. Symptoms can include weight loss, jaundice, and photosensitivity.

Inkweed is a common poisonous plant for horses

Inkweed contains toxins that can cause gastrointestinal irritation, colic, and diarrhoea in horses. It can also damage the kidneys and liver if consumed in large amounts.

African boxthorn

All parts of this plant, including the berries, leaves, and thorns, are toxic to horses. The toxin present can cause severe colic, gastrointestinal upset, and, in some cases, death.

Annual rye grass

Annual rye grass is not toxic in its own right but can be infected by a fungus called Claviceps purpurea, which produces toxic alkaloids known as ergot alkaloids that cause a condition in livestock called rye grass toxicity. These compounds can cause symptoms such as tremors, seizures, gangrene, and usually death in horses. Unfortunately, the toxins can spread to surrounding vegetation, which is why all hays grown in known infested areas should be tested.

Marshmallow weed

Marshmallow weed can accumulate high levels of nitrates, particularly when grown under certain conditions like excessive fertilization or stress. Ingesting a large volume of plants with high nitrate content can lead to nitrate poisoning, which affects the horse’s ability to transport oxygen in the blood and can result in symptoms like rapid breathing, weakness, staggers, and even death.

This list is by no means complete – many other plants are also toxic to horses. Do you research and identify which ones may be present in your area.

These plants are toxic to horses due to various toxic compounds they contain, such as alkaloids, glycosides, and amino acid toxins. Consumption, or even just touching some of them, can lead to a range of symptoms, including gastrointestinal upset, liver damage, anomia, neurologic disorders, and even death. It is essential to prevent horses from accessing areas where these plants grow and to ensure their pasture and hay are free from these toxins.

To be continued…

Find out more in Part 2 where we’ll consider how you can identify poisonous plants for horses, keep your horse safe from them, how to identify the common signs of toxicity in horses, and what to do.

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