Equis ISSN 2398-2977

Toxicity: cyanide

Synonym(s): Cyanide poisoning

Contributor(s): Birgit Puschner, Nicola Bates


  • Cause: ingestion of cyanogenic glycoside-containing plants can cause acute poisoning.
  • Signs: usually within a few hours of exposure, include apprehension, ataxia, weakness, hyperventilation, recumbency, cardiac arrhythmias and death.
  • Diagnosis: clinical signs, post-mortem findings, and analysis of feed or stomach contents.
  • Treatment: removal of toxic plants, avoid stress, and supportive care. There are antidotes for cyanide poisoning, but they may not be available.
  • Prognosis: guarded to poor.



  • Prunus spp:
    • Choke cherry (P. virginiana).
    • Black cherry (P. serotina).
    • Cherry laurel (P. laurocerasus).
    • Apricot (P. armeniaca).
    • Plum (P. domestica).
  • Other cyanide-containing plants:
    • Sudan grass and Johnson grass (Sorghum spp) Toxicity: sorghum.
    • Arrow grass (Triglocin spp).
    • Vetch (Vicia spp).
    • Corn (Zea mays).
    • Clover (Trifolium spp) Clover (Trifolium spp).
    • California holly (Heteromeles arbutifolia).
    • June berry (Amelanchior spp).
    • Eucalyptus (Eucalyptus spp).
    • Cassava (Manihot esculenta).

Predisposing factors


  • Access to cyanogenic glycoside-containing plants.


  • Highest concentrations of cyanogenic glycosides are in the leaves.
  • Young and rapidly growing plants have the highest concentrations of cyanide.
  • Plant trimmings remain toxic as long as the leaves are green and have not completely dried.
  • Insect-, frost-, and drought-damaged cyanogenic plants have been associated with a greater risk for cyanide poisoning.
  • Cyanide in mill tailing ponds at gold mines can present a risk to wild horses.


  • Hydrolysis of cyanogenic glycosides releases hydrogen cyanide (hydrocyanic or prussic acid). Hydrolysis occurs during plant cell injury or microbial action in the gastrointestinal tract.
  • Hydrogen cyanide is readily absorbed from the gastrointestinal tract, binds iron (Fe3+) in cytochrome oxidase and inhibits mitochondrial oxidation-reduction reactions, cellular respiration, and ATP production.
  • Cells with high metabolic rate and oxygen demand are particularly sensitive.


  • The onset is very variable and may be rapid (1-2 h) or delayed.
  • Animals can die within a few minutes of onset of clinical features or several hours later.


  • Access to cyanogenic glycoside-containing plants can result in herd outbreaks.
  • Clinical course can be variable within a group of horses.


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Mosing M, Kuemmerle J M, Dadak A & Moens Y P (2009) Metabolic changes associated with anaesthesia and cherry poisoning in a pony. Vet Anaesth Analg 36 (3), 255-60 PubMed.
  • Tegzes J H, Puschner B & Melton L A (2003) Cyanide toxicosis in goats after ingestion of California holly (Heteromeles arbutifolia). J Vet Diagn Invest 15, 478-480 PubMed.
  • Vetter J (2000) Plant cyanogenic glycosides. Toxicon 38 (1), 11-36 PubMed.
  • Jackson T (1995) Cyanide poisoning in 2 donkeys. Vet Hum Toxicol 37 (6), 567-568 PubMed.
  • Salkowski A A & Penney D G (1994) Cyanide poisoning in animals and humans: a review. Vet Hum Toxicol 36 (5), 455-466 PubMed.
  • Terblanche M, Minne J A & Adelaar T F (1964) Hydrocyanic acid poisoning. J S Afr Vet Med Assoc 35, 503-506.

Other sources of information

  • Panter K E (2018) Cyanogenic Glycoside-Containing Plants. In: Veterinary Toxicology. Ed: Gupta R C. 3rd edn. Academic Press, USA. pp 935-940.
  • Burrows G E & Tyrl R J (2013) Rosaceae. In: Toxic Plants of North America. Ed: Burrows G E & Tyrl R J. 2nd edn. Wiley-Blackwell, USA.
  • Wright B, Bebbington A & Leuty T (2008) Prunus Poisoning Horses and other Livestock. Ontario Ministry of Agriculture, Food and Rural Affairs, Ontario, Canada. Website: www.equineguelph.ca (pdf download ).
  • Pickrell J A & Oehme F (2004) Cyanogenic Glycosides. In: Clinical Veterinary Toxicology. Ed: Plumlee K H. Mosby, USA.


  • ASPCA Animal Poison Control Center. Website: www.aspca.org. Tel: +1 (888) 426-4435.
  • Veterinary Poisons Information Service (VPIS). Website: www.vpisglobal.com. Tel: +44 (0) 2073 055 055.