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Poisonous Plants

Cyanide-containing Plants Minimize

Sorghum/sudan grass (Sorghum spp.) and fruit trees in the Prunus spp.

OTHER CYANOGENIC PLANTS:

  • Hoecus lunatus - Velvet Grass
  • Hydrangea species - Hydrangea
  • Linum species - Flax
  • Lotus corniculatus - Birdsfoot Trefoil
  • Phaseolus lunatus - Lima Bean
  • Pyrus malus - Apple
  • Sambucus canadensis - Elderberry
  • Suckleya suckleyana - Poison Suckleya
  • Trifolium repens - White Clover
  • Triglochin maritima - Arrow Grass
  • Vicia sativa - Vetch Seed
  • Zea mays - Corn
Toxic Principle
cyanogenic glycosides or cyanogens (amygdalin, prunasin, dhurrin, linamarin)

Hydrogen cyanide (HCN) is formed when the glycosides are hydrolyzed by enzymes in plants or by rumen microorganisms:


Cyanogenic glycosides → sugar + aglycone
Aglycone → HCN + aldehyde or ketone

The glycosides occur in vacuoles in plant tissue while the enzymes are found in the cytosol. Damage to the plant from wilting, trampling, mastication, frost, drought, bruising etc. results in the enzymes and glycosides coming together causing hydrogen cyanide to be formed. b-glycosideases are also produced by rumen microorganisms. The optimal pH for enzyme activity is near neutrality, so release of HCN is more rapid in the rumen than in the highly acid stomach of monogastrics. For this reason, ruminants are more sensitive to cyanogens than nonruminants.

Toxicity
Cyanide is lethal at dosages of 0.5 to 3 mg/kg b.w. Ingestion of 100 g of wild cherry leaves with ~ 200 mg CN per 100 grams would be lethal to a 100 lb. animal.
MOTA
Once free cyanide is released from the plant tissue and is absorbed it reacts with ferric iron (+3) in cytochrome oxidase which halts cellular respiration. Oxyhemoglobin cannot release oxygen for electron transport in the cytochrome system since the cyanide – cytochrome oxidase will not function in electron transport.
Diagnosis
Clinical signs
  • Animals are commonly found dead due to rapidity of cyanide’s effects
  • When observed, signs may include excitement, general muscle tremors, dyspnea, salivation, defecation, urination followed by clonic convulsions and death.
Laboratory diagnosis
Measurement of cyanide in GI contents.
Lesions
bright red color to blood and mucous membranes, detection of plant material in GI tract.
Treatment
General
remove from source
Specific
sodium nitrite at 10 to 20 mg/kg with 500 mg/kg sodium thiosulfate as needed. The treatment is directed at breaking the cyanide – cytochrome bond with the nitrite forming methemoglobin. Methemoglobin has a greater affinity for cyanide than does cytochrome oxidase, so it strips cyanide from the enzyme. The thiosulfate then reacts with the cyanide via the enzyme rhodanase forming thiocyanate which is readily excreted in the urine.
Prevention
Test forage prior to feeding. Cyanide is volatile, so opening bales of hay 24 hours before feeding allows the cyanide to dissipate.
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