Japanese Pieris Poisoning in Horses

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

What is Japanese Pieris Poisoning?

Japanese pieris (its botanical name Pieris Japonica) is also known as Japanese andromeda and lily-of-the-valley bush and it can be quite toxic to horses. This is typically a landscape shrub from the Ericaceae family which originated in Asia and is generally found growing in the acidic soils of Eastern United States. The toxin process which takes place after ingestion can be deadly to equine with a few days if not treated.

Japanese Pieris poisoning results from horses ingesting any and all parts of the plant itself or consuming the nectar from the flowers. Its offending toxin is thought to be grayanotoxin, also known as andromedotoxin, which affects how various cells function.

Symptoms of Japanese Pieris Poisoning in Horses

The symptoms of Japanese pieris poisoning in horses come from the andromedotoxin process and these are some of the symptoms which can develop within 6 to 8 hours of ingestion of the plant:

  • Salivation which is excessive
  • Abdominal pain
  • Weakness
  • Recumbency
  • Increased heart rate
  • Increased respiratory rate - inhalation pneumonia is often a cause of death
  • Seizures and convulsions noted in severely poisoned animals
  • Coma and death


Japanese pieris poisoning results from the andromedotoxin or grayanotoxin process. This is just one of many plants in the Ericaceae family which contain the toxin which can result in severe poisoning and death of the afflicted horse. The toxin contained in Japanese Pieris has been noted to cause problems in the gastrointestinal system, renal and liver problems as well as secondary aspiration pneumonia in horses who have ingested this plant and others from its botanical family.



Causes of Japanese Pieris Poisoning in Horses

The poisoning caused by ingestion of Japanese pieris results from the chemical reaction which takes place in the digestive system. As the intestinal system digests the plant’s leaves and flowers, the andromedotoxin binds to receptor sites on various cell membranes, causing them to malfunction. The cell membranes to which the andromedotoxin binds are responsible for starting and stopping the cell as it performs its normal function in the body. The andromedotoxin interferes or interrupts this activation/inactivation process, limiting the cell’s normal function. As noted above, the cells involved are intestinal, renal, hepatic and central nervous system.



Diagnosis of Japanese Pieris Poisoning in Horses

Though the symptoms noted above are quite similar to other diseases and conditions of the equine, it is imperative that when you notice the symptoms, get medical care for your horse immediately. Also as noted above, some of the digestive symptoms can present within a few hours of ingestion and death can occur within a day or two if treatment is not initiated. The diagnostic process of this poisoning will involve a complete history from you, a thorough physical examination of the afflicted equine and most likely some blood and tissue samples for lab evaluation.

The comprehensive blood panels most likely recommended by your veterinary profession will provide insight into the likelihood of the type of poisoning and the degree to which it has progressed. This information will be utilized to develop an appropriate treatment plan. Getting the required medical intervention as quickly as possible is vital to the survival of your horse.



Treatment of Japanese Pieris Poisoning in Horses

Treatment will likely begin with removal of the horse from the source of the poisoning and quietly and calmly taking him to a safe and quiet place where abundant, clean, good quality feed and water are readily available. Calling the vet should be your next step in treatment of any horse in whom you suspect poisoning. Most likely the main treatment plan will include the steps you took to remove the horse from the source of the poisoning and then supportive care.

Activated charcoal has been used successfully to neutralize the poisoning and quiet the digestive system. Keeping the horse quiet, calm and safe will reduce the stress on the animal, stress being one of the components which is known to lead to worsening of the symptoms of poisoning. The earlier that medical intervention is provided, the better the prognosis of your horse. And, it is important to note that younger horses may be at higher risk for serious complications and death.



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Recovery of Japanese Pieris Poisoning in Horses

Getting appropriate medical care as quickly as possible is vital to the survival of your afflicted horse. If appropriate medical intervention is provided sooner rather than later, your horse will likely recover nicely, depending on the severity and the amount of the plant consumed. Prevention is your best option for protecting the rest of your herd and the best method of prevention is to first acquaint and educate yourself on what poisonous plants are germane to your area. Next, ascertain if they are in the pastures in which your allow your herd to graze. Be sure to monitor the hay being fed as well to assure that these poisonous plants aren’t mixed with good hay, especially if it was harvested from pastures. Many poisonous plants are just as toxic to your horse in the dry stage as they are in the green or fresh stage.



Japanese Pieris Poisoning Questions and Advice from Veterinary Professionals

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