Horses naturally have an instinct that indicates whether or not a plant is toxic to them. Often poisonous plants are also very unpalatable, so horses will not eat them. However, things can sometimes go wrong, causing the horse to eat poisonous plants.

One reason for this may be that a horse has insufficient access to grass or other roughage. The horse is hungry and can look for other plants to eat, including poisonous ones. Another reason may be that the poisonous plants are processed in hay or haylage. By processing this way in roughage, the horse does not recognize the plants and simply eats them. This is a big risk, especially with Ragwort. The horse can no longer recognize the plants by smell because they are dried. And this plant does not lose its toxic properties in dried form. 

There is a whole list of plants that are toxic to horses. The most notorious among horse owners is Ragwort. Most horses avoid poisonous plants, but cases of poisoning in horses do occur. The symptoms of poisoning depend on the plant the horse ate. 

Ragwort is a wild plant that is common in pastures, roadside verges and natural grassland. It has yellow flowers, a purple stem and at the bottom of the stem the leaves form rosettes. The plant contains highly toxic alkaloids (poisonous compounds found in plant material) that lead to irreversible liver damage. Often the poisoning is not recognized because it accumulates in the liver. It can take years before there is enough poison in the liver for the liver to get damaged. Ultimately, the liver damage can cause death. There are other poisonous meadow plants such as St. John’s wort (Hypericum perforatum) and Alsike clover (Trifolium hybridum). Poisoning by these two plants causes the horse to suffer burns. Alsike can also cause liver damage. 

Another notorious poisonous plant is Yew (Taxus baccata). Horses will not just eat from this bush themselves, but it can happen that the pruning waste is fed. A few bites can already cause the horse to go into cardiac arrest and die within half an hour. Boxwood is another shrub that is very poisonous, it can lead to respiratory arrest. Other poisonous ornamental plants are Laburnum, Rhododendron and Cherry Laurel (Prunus laurocerasus). Symptoms of poisoning by any of these plants range from salivation to diarrhea and from colic to imminent death. 

When it comes to poisoning, prevention is better than cure. Treatment for plant poisoning often arrives too late, or is not possible. Ensure that you implement good pasture management and do not plant poisonous plants within horses’ reach. If you use a field for making hay, check carefully for poisonous plants such as Ragwort. You don’t want this to end up in the hay. Do you not make your own hay? Then buy good quality roughage from a recognized forage company. You can ask the supplier of your hay if it is free of these plants. This is a mark of quality that they can give. It is not recommended to feed roadside hay to your horse, because it may contain many poisonous plants. It is also not wise to feed garden or pruning waste to horses, because of the poisonous ornamental plants that can be found in it. 

Summary: 

• In general, horses avoid poisonous plants
• Symptoms of poisoning differ per plant
• Prevention is better than cure
• Ensure good pasture management and good quality roughage
• Do not feed roadside hay or garden waste