Oleander toxicity

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Oleander Toxicity

Oleander (Nerium oleander) is an attractive, hardy, ornamental, evergreen shrub that is a major cause of animal poisonings worldwide. Oleander is found in tropical and subtropical regions. It has dark gray-green, leathery leaves. It's showy clusters of flowers bloom from early summer until mid-autumn.

Toxic Components

Oleander is a highly toxic plant. It contains several cardiac glycosides--the most toxic chemicals being oleandrin and neriine.
Cardiac glycoside poisoning acts by inhibiting Na+/K+ ATPase. Horses don't need to ingest very much to have fatal consequences. As little as 0.005% of its body weight in dry oleander leaves can be fatal (which equals roughly 10 to 20 leaves for an average-sized adult horse). The most frequent source for oleander exposure in livestock is yard/garden clippings. There have also been incidences where horses consumed hay that was contaminated with oleander leaves. Bored horses may also chew on plants that grow near their paddocks. Oftentimes, horses are found suddenly dead, or present with rapidly developing nonspecific signs that may resemble colic.

Clinical Presentation

If signs do appear, there is usually a 2–5-hour delay from ingestion of the plant to apparent symptoms. Signs of poisoning may begin with diarrhea, excessive salivation, depression and loss of appetite and progresses to the development of cardiac signs such as bradycardiaor tachycardia, weak and irregular pulse, heart blocks, and arrhythmias.


Muscle tremors
Colic signs
Frequently laying down
Cardiac arrhythmias
Loss of appetite
Sudden death


  • History - exposure to yard clippings or identification of oleander species in the vicinity of the horse.
  • Clinical signs
  • Necropsy - Oleandrin was detected in the stomach content.



Activated charcoal
Supportive care
Should be kept as calm as possible and placed in a quiet area
Evaluation of cardiac irregularities and possible treatment.


  • Make yourself aware of the plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.


Most cases are fatal

Scientific Research

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Risk Factors

  • Oleander that is accessible by horses either while in pastures or anywhere near the vicinity of the barn (horses do sometimes get loose).