Toxic Range plants- Acute resp disease Flashcards
What factors affect livestock plant poisonings?
-Management issues
-Stress conditions
-drought and evaporation
-Plant ID challenging
-Few diagnostic tests available
Management issues causing toxic range plant ingestion
-overgrazed pasture
-many toxic plants appear in spring
-lack of alternative feed
*livestock will often not eat toxin if adequate feed
Fog fever
3-methylindole poisoning occurs when cattle moved from dry to lush pastures (abrupt feed transition) or unknown cause in feedlot cattle
Who is most at risk for fog fever?
Cattle under 2 yrs in good body condition
-beef more than dairy
-not in calves
Fog fever target organ and mechanism
Target: lungs
Mechanism: excess tryptophan is converted to 3-methylindole by rumen microbes resulting in type 1 pneumocyte destruction= resp distress
Onset of fog fever
Within 12 hrs of consuming lush forage
-multiple animals affected
-occurs 5-10 days after movement
Clinical signs of fog fever
-dyspnea, coughing
-expiratory grunt
-mouth breathing, hypersalivation
-death in 2-3 days
50%morbidity, 25-50% mortality
Management of fog fever
No effective treatment
-can try and use NSAIDs, diuretics, bronchodilators
Diagnosis of fog fever
-history of movement to green pasture
-clinical signs and necropsy findings
-no confirmatory test
PM lesions of fog fever
-lungs fail to collapse
-edem
-emphysema
*caudodorsal region of lungs
DDx for fog fever
Acute dyspnea/resp distress
-nitrate, cyanide, urea, OP/carbamates, larkspur
Prognosis of fog fever
Depends on severity
-severe=poor
-mild=recover without treatment
Prevention of fog fever
-limit use of lush pasture
-feed hay before pasture turnout
-monensin supplementation
Nitrate poisoning
-Forage high in nitrate related toxicity OR ingestion of nitrate fertilizers/agricultural run off or contaminated water
How do plants become high in nitrate
Nitrate is the major form of nitrogen in the soil that plants take up and use for photosynthesis
*lower stem higher than upper and leaves
Nitrate accumulating plants
-hay cut during nitrate accumulation period
-green feed oats, oat hay
-stubble fields like canola and corn
What conditions increase nitrate accumulation due to decreased photosynthesis?
-drought
-freeze/thaw
-damage
-herbicides
Target organ and mechanism of nitrate poisoning
Target: RBCs
Mechanism: oxidation of hemoglobin leading to methemoglobin (MetHb). Means inability to carry oxygen
Why are ruminants most susceptible to nitrate poisoning?
Excessive nitrate converted to excessive nitrite. Nitrite is 10x more toxic and is absorbed from rumen into bloodstream
Clinical signs of nitrate poisoning
- sudden death- multiple cattle found dead after introduction of need feed or after grazing stressed forages
- Acute= resp distress secondary to asphyxiation
- chocolate brown blood
Nitrate toxicity management
-Medical emergency
-Antidote= methylene blue (reduce MetHb to Hb)
-remove animals from suspected pasture
Diagnosis tests of nitrate poisoning
-Antemortem: MetHb in whole blood
*nitrate/nitrite has a short half life in blood
-Postmortem: ocular fluid
-Environment= test feed, water
DDx of nitrate poisoning
Acute resp distress and sudden death
-cyanide, AIP, urea, cardiotoxic plants, ionophores
Prognosis of nitrate poisoning
poor for livestock with acute respiratory distress
Cyanide poisoning
-forage related, plant trimmings, fallen trees
-contained in plant vacuoles and released when plant damaged (leaves, bark, stems, seeds highest)
Factors affecting cyanide accumulation
1.any damage to plant
2. regrowth after impaired growth/poor growth
3. young plants
4. trampled, wilted plants
5.hail damage
6. high nitrogen and low phosphorus soil
Cyanide toxicity target and mechanism
Target: heme groups
Mechanism: inhibits ETC and inactivates Hgb= asphyxiation
Why are ruminants most susceptible to cyanide poisoning?
-Rumen microbes hydrolyze cyanogenic glycosides, increasing free cyanide in the ruminant
Clinical signs of cyanide toxicity
- sudden death or found dead after grazing stressed forages
- resp issues, tachycardia, tremors/seizures
- bright red blood
Cyanide management
-medical emergency
-intensive care in hospital
-antidotes= Sodium nitrite, sodium thiosulfate OR hydroxocobalamin
Cyanide diagnosis
-cherry red blood **
-collect rumen in airtight container and test
-test forage
-plant ID on pasture or in rumen
