Horsetail Poisoning in Horses

Horsetail Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Horsetail Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Horsetail Poisoning?

The plant is not attractive for your horse to eat, but it may get mixed up in the hay making process and the contaminated hay will cause poisoning. Because of its high silicate content, it is not the preferred food for your horse. This plant is considered a living fossil, as it has been around since the Palaeozoic era (about 250-540 million years ago) Poisoning first shows as a general dullness to the haircoat, followed by slightly uncoordinated movements. If it is not treated, loss of muscle tone and control follows. Recovery is possible if caught early and treated.

This ancient fernlike plant is found in warm temperate climates. The plant can have a detrimental effect on your horse if eaten in large quantities.

Symptoms of Horsetail Poisoning in Horses

  • Nervousness of your horse as it copes with a degenerating system 
  • Staggering movements
  • Imbalance 
  • Inability to get up once your horse lies down 
  • Loss of weight and wasting away
  • Paralysis
  • Convulsions
  • Loss of muscular control 
  • Anxiety 


  • The toxin in this plant is not really understood, but it is known to inhibit the production of Vitamin B1 which is vital for your horse to extract energy from carbohydrates, proteins and fats
  • It has a high silicate content which is not palatable to your horse
  • This noxious plant is known as Equisetum arvense 
  • It is toxic even when dried


Causes of Horsetail Poisoning in Horses

  • Horsetail is found in pastures, wet areas, banks of the stream and makes itself at home in sandy wet soil
  • Poisoning by contamination (this plant can sometimes get mixed in with hay during hay cultivation) 
  • Young horses often experiment with eating new plants and this can lead to toxic results 
  • Horsetail often grows in late spring 


Diagnosis of Horsetail Poisoning in Horses

The symptoms affecting your horse are hard to miss, and keen observation of the grazing field may reveal horsetail flourishing within the grass. This plant is a survivor and has roots that grow down a long way into the soil so pulling it out is not an option – if you leave any roots it will regrow with vigour. Remove your horse from horsetail infected growth, for peace of mind it would be advisable to get your veterinarian out to confirm the symptoms are from eating the toxic plant. After giving your horse a physical examination, your veterinarian may prescribe a treatment which involves laxatives to rid the eaten food quickly from the system.

Following this, an intramuscular injection can be administered to build up vital vitamin B1 levels. But like many plant related illnesses prevention is always better than having to treat your sick horse. It is vital to remain on the alert for windblown seeds taking root and infesting the grasslands. These noxious plants seem to spread very easily and will soon take over the paddock unless steps are taken to keep them out.



Treatment of Horsetail Poisoning in Horses

There is no known proven formula or treatment for your horse if it has been poisoned by field horsetail. If your horse is removed from the pasture in the early stages of toxic ingestion, then a good chance of a full recovery is possible. There have been many case studies where the affected animal recovered after a bout of poisoning, the determining thing was the extent to which the horse had been affected, and how much of the weed had been eaten. Therefore, observing your horse’s behavior is vital to pick up on the early signs of a problem.

Keep in mind that these toxins can build up in your horse over time, until it reaches the critical point when your horse will succumb to it. This is why it is vital to catch it early. Allowing your horse to recover with quality food, good nutrition, and fresh water will aid recovery. Your veterinarian may prescribe treatment of large amounts of thiamine to overcome the toxic effects. This is because the toxin destroys Vitamin B1 causing a deficiency. It also interferes with carbohydrate metabolism which results in weight loss and other symptoms.



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Recovery of Horsetail Poisoning in Horses

Your horse may need to be stabled while it overcomes the effects of eating the horsetail plant. It takes time for a toxic weed like this to pass through the system and allow the animal to recover. With care, your horse can return to good health rapidly. Pasture management is vital to ensure no noxious weeds are creeping into the grass. While you are checking your paddock, check over the fence to ensure the horsetail is not coming from there. The plant is not attractive to eat, nor does it taste good to your horse. They will only eat it if they are exceptionally hungry, for example, it the pasture has been overgrazed and there is a lack of food. Most poisonings are accidental – that is the animal has eaten hay that has come from a paddock where the plant was growing.



Horsetail Poisoning Questions and Advice from Veterinary Professionals

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