• Cause: ingestion of cyanogenic glycoside-containing plants can cause acute poisoning.
• Signs: usually within a few hours of exposure, include excitement, apprehension, ataxia, weakness, hyperventilation, salivation, diarrhea, 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 in adequate time to be useful.
• Prognosis: guarded to poor.

• Sudden onset of distress.
• Weakness, ataxia, tremors, recumbence.
• Dyspnea, hyperpnea.
• Hypotension.
• Cardiac arrhythmias Dysrhythmias.
• Seizures Seizures.
• Sudden death.

• Usually within 10-20 min of ingestion.

• There are many plants worldwide that contain cyanogenic glycosides, and poisoning can occur anywhere these plants grow.

• Death may be rapid but multiple animals may be involved.

• Plants:
  • Prunus spp:
    • Choke cherry (P. virginiana).
    • Black cherry (P. serotina).
    • Cherry laurel (P. laurocerasus).
    • Apricot (P. armeniaca).
    • Plum (P. domestica).
    • Apricot.
    • Peach.
    • Pincherry.
    • Ornamental cherry.
    • Nectarines.
    • Almonds.
    • Bird cherries.
    • Black thorn.
  • Other cyanide-containing plants:
    • Sudan grass and Johnson grass (Sorghum spp).
    • Arrow grass (Triglocin spp).
    • Vetch (Vicia spp).
    • Corn (Zea mays).
    • Clover (Trifolium spp).
    • California holly (Heteromeles arbutifolia).
    • June berry (Amelanchior spp).
    • Eucalyptus (Eucalyptus spp).
    • Cassava (Manihot esculenta).
    • Acacia greggii (guajillo).
    • Amelanchier alnifolia (western service berry).
    • Linum spp (linseeds and flaxes).
    • Sambucus nigra (elderberry).
    • Poison suckleya (Suckley suckleyana).
    • Marsh arrow grasses (Triglochin maritima and T. palustris).
    • Heavenly or sacred bamboo (Nandina domestica).
    • Lima beans (Phaseolus lunatus).
    • Bird’s-foot trefoils.
    • Hydrangeas (Hydrangea spp).
    • Bracken fern (Pteridium aquilinum).
    • Bahia (Bahia oppositifolia).
    • Flowering quince (Chaenomales spp).
    • Laurel (Prunus laurocerasus).
    • Linseed – must be heat treated to feed safely to cattle.
    • Herbal leys have become popular in some communities and these may potentially contain a mix of plants containing various toxins.
• Fertilizer (cyanamide).
• Pesticides/rodenticides (calcium cyanomide) Rodenticide poisoning: availability of chemicals varies between countries but bear in mind that even in countries where certain chemicals are now banned, there may be old containers still to be found on farms.
• Smoke from chemical fires, including burning vehicles Smoke inhalation.
• Cyanide in mill tailing ponds at gold mines can present a risk to cattle grazing nearby.

General

• Access to cyanogenic glycoside-containing plants.

Specific

• 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 prevents hemoglobin in erythrocytes from releasing oxygen to the tissues, so animals ultimately dying of anoxia.
• 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.
• Beta-glucosidase and hydroxynitrile lyase are present in the rumen microflora. A healthy rumen pH of ~6.5-7 allows conversion of cyanogenic glycosides to cyanide. Cattle on energy-dense rations may have subacute ruminal acidosis Subacute ruminal acidosis and although usually associated with poor health/husbandry, the lower rumen pH in such animals may in fact have some protective effects against the formation of cyanide in exposed animals.

• The onset is very variable and may be rapid (10-20 min) 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.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Kennedy A, Brennan A, Mannion C & Sheehan M (2021) Suspected cyanide toxicity in cattle associated with ingestion of laurel – a case report. Ir Vet J 74 (1), 6 PubMed.
• Ufaysa Gensa (2019) Review on cyanide poisoning in ruminants. J Biol Agriculture Healthcare 9 (6), 1-12 CORE (pdf download).
• 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 (5), 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

• Cope R B (2021) Cyanide Poisoning in Animals. MSD Manual, USA. Website: www.msdvetmanual.com.
• Panter K E (2018) Cyanogenic Glycoside-Containing Plants. In: Veterinary Toxicology. Ed: Gupta R C. 3rd edn. Academic Press, USA. pp 935-940.
• National Pesticide Information Center (2016) Rodenticides Topic Fact Sheet. Website: www.npic.orst.edu
• 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.
• HSE (online) Rodenticides. Website www.hse.gov.uk.

• 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.