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What is Rhododendron Poisoning?

Plants in the rhododendron genus can be found throughout the United States. They contain toxins known as cardenolides or cardiac glycosides. These toxins will obstruct the natural rhythm of the heart, irregularities or arrhythmias will result. Death will occur without seeking medical attention. Toxins are found in all parts of these plants with the highest concentration being in the fruit, flowers and immature leaves. The toxicity remains even when the plant is dried.

Since rhododendron is generally not very palatable to horses, they will leave it alone unless they are on a sparse pasture. To avoid your horse from developing rhododendron poisoning, make sure that their pasture has plenty of nutrient rich forage and is not being over-grazed.

Rhododendron is a genus of plants that are characterized by shrubs to small trees. They have leaves that are spirally arranged and may be covered with scales or hairs. Plants may be evergreen or deciduous. Many rhododendron plants are noted for their clusters of large flowers, such as the azalea.

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Symptoms of Rhododendron Poisoning in Horses

Since rhododendron poisoning includes plants that are known cardiac glycosides it is extremely important to seek immediate veterinary attention if you suspect your horse has ingested any plants that are included in the rhododendron genius. Symptoms to watch for include:

  • Diarrhea
  • Hyper-salivation
  • Weakness
  • Coma
  • Loss of appetite
  • Colic
  • Leg paralysis
  • Depression
  • Loss of coordination
  • Cardiovascular collapse
  • Seizures
  • Death

Causes of Rhododendron Poisoning in Horses

Plants within the rhododendron genus contain cardiac glycosides. Cardiac arrest occurs when your horse ingests the plant and then becomes stressed or excited. Four organ systems are affected when a horse ingests any plants in the rhododendron genus: the gastrointestinal tract, the cardiovascular system, the neuromuscular system and the respiratory system. Sudden death will occur in many cases since the horse is quickly affected by the poisoning. There have been many horse owners who have found their horses dead, still in their pastures. 

Preventing rhododendron poisoning is the only way to ensure that your horse will remain healthy. Doing regular pasture checks for poisonous plants and quickly eradicating them will keep your horse away from these poisonous plants.

Diagnosis of Rhododendron Poisoning in Horses

When you suspect that your horse has ingested a plant from the rhododendron genus, contact your veterinarian immediately for an emergency visit. While you are waiting for your veterinarian to arrive, collect any plants that you think your horse ingested, along with a sample of the hay that your horse has eaten.

Your veterinarian will conduct a full physical examination of your horse. They will ask you questions regarding the symptoms that you have seen. A fecal examination, urinalysis, and complete blood count will also be done to conclusively determine the cause of your horse’s illness.

Treatment of Rhododendron Poisoning in Horses

Treatments will begin as soon as rhododendron poisoning has been diagnosed. Your veterinarian will speak with you about your options for treatment and help you decide which the is the best for you and your horse. 

Hospitalization will be strongly recommended to begin supportive care. An IV will be inserted to make administering medications easier and less stressful on your horse. Fluid and nutrition therapy will also be provided. While in the hospital, the veterinary staff will try to keep your horse from becoming overly stressed. Too much stress will cause your horse to experience a cardiac episode that could be fatal.

Your veterinarian may administer a dose of activated charcoal, by mouth, to your horse. This is usually effective in absorbing any plant toxins that are still in your horse’s stomach. 

Anti-arrhythmia drugs may be given through the IV if your horse is experiencing any cardiac irregularities. Magnesium sulfate can be administered by mouth to treat ventricular arrhythmias.

Recovery of Rhododendron Poisoning in Horses

The prognosis for a horse suffering from rhododendron poisoning is very poor. Once treatments have begun, your veterinarian will be able to give you a more accurate prognosis based on your horse’s reaction to treatments.

Horses that recover from rhododendron poisoning may have long term effects that prevent them from returning to normal activities. Permanent heart damage has been reported in many horses who have recovered from this poisoning.

Prevention is the best way to avoid rhododendron poisoning. Eradicating any plant within the rhododendron genius from your pasture or any area your horse is allowed will prevent this type of poisoning. If you are unsure if a plant is poisonous, research that plant or ask an expert. Pasture safe herbicides can be used to kill any unwanted weeds or plants.