Yew toxicity

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Yew Toxicity

Yew Poisoning

Yew (Taxus spp.) are a common ornamental tree or shrub found worldwide, often used as hedges. In its tree form, Taxus spp are densely branching evergreens with a massive trunk, reaching up to 20 m tall. The leaves are dark green, linear and up to 3 cm long, with a pointed tip, and appear to spread in two rows on either side of the shoot.

Yew toxic components
All parts of Taxus spp. are very poisonous and contain a complex mixture of alkaloids. Taxines A and B are two of the major chemicals found in the mixture, which is absorbed rapidly and interferes with calcium channels in cardiac myocytes, resulting in cardiac arrest and death within 30 minutes of ingestion. Other toxins that are also found in Taxus spp. are ephedrine, a cyanogenic glycoside (taxiphyllin) and a volatile oil.

Consumption of as little as 0.1% body weight in Taxus spp. leaves is lethal to horses. Symptoms are rarely observed since horses die quickly following ingestion. Most cases have resulted from horses gaining access to yard/hedge clippings. Taxus spp. is one of the plants where the poison is not destroyed when the plant dies. Thus, branches removed from a yew by high winds or pruning will retain their poison.

Taxus spp have caused many poisonings in livestock since ancient times. Plants of Taxaceae, or yew family are known to be palatable to horses. Risk of toxicity increases during the winter months, as the palatability and concentration of toxins increases in the leaves.

Symptoms

Ataxia
Trembling
Collapse
Abnormally low heart rate
Mild colic
Diarrhea
Sudden death

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Necropsy

Treatment


TreatmentDetails
Activated charcoal
Supportive care

Prevention

  • Do not plant yew trees anywhere near horses.
  • Be mindful not to dispose of yew tree clippings in areas where horses could access them.
  • Make yourself aware of the weeds and 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.
  • Do not put Christmas decorations which could potentially contain yew evergreen, anywhere near where horses can access it.

Prognosis

Poor

Scientific Research References

Good Overviews

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Risk Factors

  • Hanging up Holiday decorations made from the yew tree that are accessible to horses.
  • Allowing horses access to yew trees in horse pastures or planting near horse stables.

Also Consider