How can I protect my horse from poisonous plants?

Hoary alyssum

Alongside black locust, the most common cases of poisoning occurring in Germany are caused by hoary alyssum (in pasture) (Drozdzewska et al., 2024). 

Poisoning with hoary alyssum (berteroa incana) is only moderately toxic to horses. However, cases are becoming more frequent: particularly in drier regions, where the plant occurs on more than half of horse pastures in some cases and can also make up a considerable proportion of the vegetation. 

Hoary alyssum is very robust and resistant to ultraviolet radiation. Warm and dry summers therefore favour its spread – very much to the detriment of heat-sensitive pasture plants. The young plant does not yet taste bitter in spring. Hoary alyssum remains toxic even when dried in hay. 

Symptoms: Oedema, gastrointestinal irritation and colic can be symptoms of poisoning. 

What helps: Pastures and meadows with controlled grazing, regular fertilisation and more intensive use are generally less affected.

Common ragwort

Common ragwort (jacobaea vulgaris), also known as tansy ragwort, is dangerous for horses. The stems of the plant are reddish at the base and otherwise green. You can recognise the plant by its bright yellow flowers, which grow in umbels. It reaches a height of 20 to 130 cm. Common ragwort is mainly found along roadsides and railway embankments, as well as in fields and damp meadows. However, it can also occur in nutrient-poor paddocks. For your horse, common ragwort is particularly dangerous when ingested over a long period, even in small quantities. In the paddock, it is normally not grazed along with other plants. However, the plant is extremely insidious: it remains toxic even in hay and silage, and in this form it is eaten unnoticed by horses.

Symptoms: Symptoms can include, for example, loss of condition and weight, loss of appetite, colic, liver damage, lethargy, restlessness, etc. In the worst case, death occurs due to liver failure.

What helps: When controlling common ragwort, it is important to prevent it from seeding. To do this, the first individual plants must be removed as early as possible. Since common ragwort flowers between June and September, removal should begin in early summer. Thorough pasture maintenance, fertilisation, more intensive use and overseeding are the best methods of control.

Black locust

Black locust trees (robinia pseudoacacia) are highly toxic to horses and popular as ornamental trees – so it comes as no surprise that, alongside hoary alyssum, they are responsible for the most common cases of poisoning in Germany after consumption (Drozdzewska et al., 2024), whether the tree grows as an ornamental on the yard or wild in the pasture. 

The tree is drought-tolerant and extremely resilient. The plants accumulate their toxin primarily in the seeds and the bark. 

Symptoms: As little as 70 g of bark can cause gastrointestinal disturbances, while 100 g of bark is likely to cause disturbances of the central nervous system (CNS). 

What helps: Black locust trees should not grow in your horse’s pasture. We also advise removing the wood of felled trees. Your horse must not have access to black locust in the yard either.

Foxglove

Foxglove (digitalis) is an extremely poisonous plant. As little as 25 g of dry matter in hay or 150 g of fresh leaves can be fatal to horses. Foxglove grows in mountain forests, open woodland, gardens and on sunny slopes. It has bell-shaped, red flowers ─ the flowering period is in August. The plants grow to between 30 and 150 cm in height. 

Symptoms: After ingestion, symptoms such as colic, bloody watery diarrhoea, bloody urine, drowsiness, muscle tremors, staggering and rapid breathing may occur, and death from cardiac arrest can result. Foxglove is also extremely dangerous for humans: a dose of just two leaves can be fatal. 

What helps: As foxglove is a protected species, it may not simply be removed. You can transplant it from the horse pasture to other areas not used for grazing, or fence off the areas of the paddock where foxglove grows – however, given the already limited grazing areas available, this is usually difficult to put into practice.

Sycamore maple

Seeds of the sycamore maple (acer pseudoplatanus) or also Norway maple (acer platanoides) contain the toxic substance hypoglycin A. If horses ingest the toxic seeds themselves or seedlings, symptoms of poisoning can occur, also known as atypical myopathy. 

Symptoms: The leading symptom is the massive destruction of the muscles. The released muscle pigment also discolours the urine brown. Further symptoms are signs of colic, sweating, stiff gait or muscle tremors, increased respiratory and heart rate, up to recumbency and death, often within 72 hours. Horses even try to eat right up to the end while recumbent. Young horses are frequently affected. 

What helps: To prevent your horse from eating the toxic plant parts, feeding additional hay is usually sufficient for pastured horses. This prevents the ingestion of the “smallest feed remnants”, and thereby also the toxic seeds, when pasture growth is sparse. It is of course safer if the trees are removed or stand far enough away from the paddock. Otherwise, the only remedy is to thoroughly remove the seeds and seedlings of the sycamore maple. Water into which the seeds fall also contains the toxins. In addition, maple seeds also remain toxic in hay and silage. In addition to hay feeding, an optimum supply of selenium and vitamin E is important for the horses.

Marsh horsetail

As its name suggests, marsh horsetail (equisetum palustre) is found in damp meadows and along riverbanks. It can be recognised by its narrow green shoots, from which narrow, roundish leaves emerge, arranged in tiers. Marsh horsetail closely resembles field horsetail, which, however, is not toxic. On the contrary: it is even used in natural medicine. You can recognise field horsetail by the fact that it grows in different locations: it is found predominantly in fields and meadows, but can also be found at field margins and on lawns. Unlike marsh horsetail, it therefore prefers dry locations. 

Symptoms: Marsh horsetail causes so-called “staggers” in horses, which manifests itself through strong agitation, twitching of the head muscles, movement disorders, muscle tremors and paralysis of the hindquarters. Horses with a tendency towards metabolic disorders are particularly susceptible. The plant also has a strongly toxic effect in hay and silage.

Yew

The yew (taxus) is another plant that is extremely toxic to your horse. It is also dangerous for humans. The black, poisonous seeds of this evergreen conifer are surrounded by a red aril. The variety native to Europe bears the Latin name “taxus baccata”.

Symptoms: In horses, even the ingestion of small amounts (100 to 200 g of needles) can lead to death within a few minutes. Poisoning can cause colic, trembling, convulsions and increased salivation. However, it is not only the needles of the yew that are toxic – the seeds, wood and bark also contain the toxin taxine. In humans, simply inhaling the pollen can trigger a strong feeling of dizziness. 

What helps: Yews have no place in pastures or riding facilities. Even cut yew branches require the greatest caution, as they remain highly toxic. They must never be disposed of in pastures!

Box tree

It is often found in gardens, parks or as tournament decoration – frequently trimmed into artistic shapes. However, box (buxus) is highly toxic! Eating just 700 to 900 g of leaves can be fatal for a full-grown horse.

Symptoms: Poisoning manifests itself through colic, severe diarrhoea, movement disorders, cramps or symptoms of paralysis. Death occurs due to cardiac and respiratory paralysis.

What helps: As with yew, the same applies to box: avoid the risk and do not use box on the premises. Particular caution is required near gardens and in parks, where box is often used as a bed border.

Thuja

Thuja, also known as the tree of life, is often used as decoration at competitions, just like box trees. The leaves are arranged in a scale-like pattern and display light or dark shades of green. However, this evergreen plant also has a very high level of toxicity.

Symptoms: Thuja is particularly dangerous for pregnant mares, as poisoning can trigger uterine cramps in the final third of pregnancy. Further signs of poisoning include salivation, colic, diarrhoea and cramps. A dose of more than 500 g of thuja can already trigger respiratory paralysis and lead to death.

What helps: Just as with box, thuja should not be planted as competition decoration or as a hedge. Particular caution is also advised around private gardens, parks or cemeteries.

Cherry laurel

The popular cherry laurel (prunus laurocerasus) is also life-threatening for your horse. If 0.5 to 1 kg of leaves are eaten at once, this can lead to death. In addition to the leaves, the fruits are also highly toxic. The plant, also known as cherry laurel, develops creamy white, candle-like, upright flower spikes in spring, from which small, black berries develop by August. Chewing the plant releases hydrocyanic acid in the stomach.

Symptoms: Poisoning manifests itself through increased salivation, accelerated breathing, and mucous membranes that first turn bright red and then bluish. In extreme cases, ingestion of the poisonous plant can lead to death within seconds.

What helps: As cherry laurel is frequently used as an ornamental shrub in gardens and parks in this country, particular caution is advised when out riding.

Autumn crocus

The beautiful autumn crocus (colchicum autumnale) is regarded as the most poisonous grassland plant and is frequently found in species-rich, extensively used and damp meadows. 1,200 g of the fresh plant is considered lethal. The plant parts also remain poisonous in silage and hay.

Symptoms: Poisoning occurs repeatedly, which can lead to mucous membrane inflammation, colic, bloody diarrhoea and, later, muscle paralysis, respiratory arrest and death.

What helps: Suitable control measures include digging out individual plants in early May or, in the case of heavy infestation, topping cuts or intensive trampling grazing in April, e.g. by sheep.