Which plants support and which plants are toxic to our horses?

Which plants support and which plants are toxic to our horses? A great interest in plants that heal took place in the 16th and 17th centuries. This led to several important herbals. The image is from that of John Gerarde (1634), frontispiece above.

The number of different species of wild plants declined in the countryside. And so has our general knowledge of their properties. Herbals in the 17th Century were commonplace. They summarised knowledge about the nature of plants and their healing properties. Gerarde’s Generall Historie of Plantes (1593) is a famous example. Culpeper’s The English Physitian, later renamed The Complete Herbal, is also famous. The Herbal by Culpeper (1652) gave detailed information about what could be eaten. And which parts of each plant had medicinal uses.

Not all herbs are beneficial

Whilst many medicines are based on plants, not all herbs are beneficial. Many are toxic for both humans and animals. Horse pastures used to have a much wider variety and composition of herbs than is the case today. Before the 1940’s, a meadow may have contained over a hundred different varieties of plant. This compared only ten species in a modern pasture”, (Allison, 1997, revised 2011). 


For example, of Apples, Culpeper tells the reader that: “They are very proper for hot and bilious stomachs, but not to the cold, moist, and flatulent. The more ripe ones eaten raw, move the belly a little; and unripe ones have the contrary ef ect. A poultice of roasted sweet apples, with powder of frankincense, removes pains of the side: and a poultice of the same apples boiled in plantain water to a pulp, then mixed with milk, and applied, take away fresh marks of gunpowder out of the skin…Roasted apples are good for the asthmatic; either raw, roasted or boiled, are good for the consumptive, in inflammations of the breasts or lungs…” Apples are said to clean the liver, cure constipation, and tone the gums. A half and half mixture of apple cider vinegar and water make a rinse to restore hair, scalp and skin.

The diversity of meadow plants has decreased.

The diversity of meadow plants has decreased. The need to identify toxic plants disappeared, also diminished. Plant diversity in natural pastures with wilding and organic farming is now increasing. This mirors changes in the way in which land is more generally cultivated. This includes the return of toxic varieties. For these reasons it is important to be able to identify the species in one’s pasture. In this way we can assess the risks for our horses. 

The most common toxic plants for horses are thought to be Ragwort, Laburnum, Bracken, and Yew. We will look at why these are toxic in a future posts. There are, however, a large number of other plants that are toxic to varying degrees.

In his book, “A guide to plants poisonous to horses” Keith Allison has offered great service. He guides the horse carer through some 50 of the most common species which pose problems for equines. 

As many know, horses (indeed all animals), are capable of self-medication through zoopharmacognozy. The horse depends upon a pasture rich enough in helpful varieties which they can select. A horse-carer wishing their horses to self-select must encourage a healthy pasture. This, in itself, reduces the risk of horses ingesting toxic varieties. One of the highest risks lies in weed-infested, horse-sick paddocks. Here, horses are driven to ingest species that they would not normally eat. These plants are normally avoided by horses.

The question of water balance

Another issue affecting potential plant toxicity, is water balance. Under drought conditions, the toxin concentrations of certain plants may increase. Here, the plant becomes more toxic for a given mass ingested. Other species, can become more toxic in wet weather, so this is also something to look out for in very moist areas. Highly invasive species ( docks, ragworts, and buttercups) grow successfully in highly grazed pastures. Docks, with their deep tap roots drain the soil of both water and nutrients. They reduce the capacity of the soil to support grasses. As the grass struggles, so these invasive varieties proliferate. This makes it more likely that horses might eat them for want of other sources of nourishment.

Classes of toxins

Whilst many plants are toxic, they are not all toxic in the same way. There are five main classes of toxins that may affect horses. These are the Alkaloids, the Glycosides, Nitrates & Nitrites, Oxalates, and the Photosensitives. In a future article, I will look at each class in more detail. I will give examples of how each class of chemical acts, and some idea of representative species.

Other articles about plants appear on my Professional Facebook Page.
If there is a plant you would like me to write about, please get in touch via Contacts.

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A guide to Plants Poisonous to Horses
Allison, K.,(2011, first edition 1997) 
J.A. Allen, London.

The Herball or Generall Historie of Plantes
John Gerarde (1597), London.

The English Physitian, 
later renamed as The Complete Herbal
Nicholas Culpeper, (1652), London.


Dr Peter Jeffs received his Diploma in Systematic Kinesiology in 2016, from the Bristol School of Advanced Kinesiology). He specializes in working with horses. He holds an Honours degree in Botany from Durham University (UK), a PhD. from Cambridge, and currently studies Permaculture with the Ecological Land Management Mastery Program, based in NORCAL, USA. He aims to bring his knowledge of Kinesiology to working with horses, herbs, and land. He is based in Wiltshire, UK, near Avebury.

He also runs an active Facebook page that shares much information about plants, horses, and wellness