FAC27: Farm Animal Toxicology (Plant Poisons) Flashcards
(43 cards)
What are the common causes of plant toxicity cases?
- Poor pasture availablity
- Overgrazing/poor pasture management
- Forage conservation
- Accessibility to poisonous plants
- Grazing experience
- Transportation
- Environmental factors
- Species suceptibility
What are the different types of plant toxins?
Alkaloids
Glycosides
- Cyanogenic glycosides
- Goitrogenic glycosides (glucosinolates)
- Cardiac glycosides
- Saponins
Nitrates/Nitrites
Oxalates
- Photosensitising agents
- Primary
- Hepatogenous
Proteins, peptides, and amino acids
Tanins
How do alkaloids cause toxicity?
They are structurally similar to ACh, dopamine, and serotonin > mimic or block the action of neurotransmitters
How do cyanogenic glycosides cause toxicity?
Cyanogenic plants contain an enzyme system capable of converting glycosides to hydrocyanic acid > inactivates the cytochrome oxidase system in mitochondria > starves cells of oxygen
How do goitrogenic glycosides cause toxicity?
Glucosinolates interfere with thyroid hormone synthesis. Thiocyanates impair uptake of iodine by the thyroid gland.
They cause goitre, reduced growth rates, and/or diarrhoea
How do cardiac glycosides cause toxicity?
They have a specific action on the myocardium, increasing contractility and slowing the heart rate > heart problems.
How do saponins cause toxicity?
absorbed very slowly but can cause gastroenteritis
How do nitrates/nitrites cause toxicity?
Nitrites are formed in the rumen after ingestion of nitrate from soil
Absorbed nitrites combine with haemoglobin in the blood to form methaemoglobin, which is incapable of transporting oxygen > anoxia
How do you differentiation HCN poisoning from nitrite poising?
Nitrate: blood is dark brown in colour
HCN: bright red
How do oxalates cause toxicity?
Rumen absorbes free oxalate and precipitates calcium oxalate crystals in submucosal arteries > damages lung capillaries and causes pulmonary oedema, nephrosis (due to crystals), hypocalcaemia
How does photosensitisation cause toxicity?
Accumulation of photosensitive metabolites under the skin and their reaction with sunlight to cause necrotic damage
How does primary photosensitisation cause toxicity?
Movement from poor to lush green pasture and fail to adapt to increased amounts of chlorophyll
How does secondary photosensitisation cause toxicity?
Biliary excretion of phylloerythrin (a normal degradation product of chlorophyll that is normally excreted in bile) is obstructed due to various liver diseases
How do the amino acids in Brasscia crops cause toxicity?
The amino acid S-methyl cysteine sulfoxide (SMCO) is converted in the rumen during normal fermentation to dimethyl disulphide. This metabolite causes poor growth rates and haemolytic anaemia.
How do tanins cause toxicity?
Hydrolysable tannins are broken down to toxic metabolites in the digestive tract of cattle and sheep
How do you treat cyanogenic glycoside toxicity?
IV sodium thiosulphate and sodium nitrite
How do you treat goitrogenic glycoside toxicity?
Glucosinolate induced goitre cannot be managed by iodine supplementation, while thiocyanate induced goitres can
How do you treat cardiac glycoside toxicity?
Supportive fluid therapy, atropine, and propranolol
Oral administration of charcoal and rumenotomy have been effective
How do you treat nitrite toxicity?
IV infusion of methylene blue
How do you treat oxalate toxicity?
Short term: calcium borogluconate therapy
But most relapse and die
How do you treat photosensitising agent toxicity?
Remove from sun
How do you treat tanin toxicity?
Liquid paraffin with milk, mucilage, and appetite stimulants
Saline purgatives are contra-indicated because of kidney damage
What plants contain alkaloids?
Yew, Laburnum, Ragwort, Hemlock, Lupin,
What plants contain cyanogenic glycosides?
Linssed and Cherry Laurel
