Feed and water related toxicants--NPN Flashcards
3 main feed/water-related toxicants?
- Non-protein nitrogen (NPN)
- Ionophore
- Water deprivation–sodium salt
Sources of NPN toxicosis?
- Urea is most commonly used
- Excess urea in feed as an additive
- Inadequate concentrates
- Contamination of feed by urea fertilizer
- Ammonium salts and ammoniated feed products
NPN toxicosis causes liberation of what?
Ammonia
One part urea produces what?
About 3 parts protein
What does urea by urease (rumen microflora) change to?
Ammonia (NH3) and CO2
What does ammonia aminate?
Ammonia aminates ketoacids (from soluble carbohydrates) to amino acids
In NPN toxicosis, what do amino acids form? What does that then converted to?
Amino acids form bacterial protein, which is then converted to animal protein
What enhances hydrolysis of urea by urease?
Alkaline pH (urea is basic)
Most susceptible species to urea toxicity?
Ruminants (horses also susceptible)
Which is the most toxic of all NPN compounds?
Urea
What is the usual urea concentration of the grain and total ration?
- 3% of the grain ration
- 1% of total ration
Which animals are more tolerant to NPN?
Animals that are adapted or preconditioned to NPN
What are the toxic doses of NPN?
- Toxic dose in not preconditioned/adapted = 0.45g/kg
- Lethal dose in adapted animals = 1-1.5g/kg
How do age, fasting, and hydration status affect NPN toxicity?
- Age
- Animals <1 yr are more sensitive
- Very young animals (3-6wks) are tolerant
- Fasting
- Increases toxicity
- Dehydration or low water intake
- Increases toxicity
What are 3 other things that increase NPN toxicity?
- Feeds rich in urease (soybeans)
- Hepatic insufficiency
- Diet low in energy and protein but high in fiber
Is all ammonia produced in the rumen toxic?
No–ammonia produced in the rumen at normal pH (5-6.5) is in the ionized form (NH4+) which is not absorbed
What does too much urea and ammonia in the rumen result in?
- Results in elevation of the rumen pH (8-9) and ammonia is in the non-ionized form
- Non-ionized ammonia is absorbed and is converted by the liver to urea which is excreted in the urine
- Too much ammonia (more than the capacity of the liver) will produce hyperammonemia
- Non-ionized ammonia crosses cell membranes, the blood brain barrier, and the placenta
Mechanism of action
Toxicity of urea is due to what?
Ammonia
Mechanism of action
What does ammonia inhibit?
Ammonia inhibits the citric acid cycle–> lack of energy and decreased cellular respiration and tissue damage
Mechanism of action
What all does NPN toxicity increase?
- Blood ammonia
- Anaerobic glycolysis
- Blood lactate and systemic acidosis
- Blood glucose
- BUN
- Serum potassium and phosphorus
- Transaminases and PCV
Mechanism of action
What might be the cause of death with NPN toxicosis?
Cardiac or respiratory failure
Clinical signs of NPN toxicosis?
- Rapid onset (0.5-3hrs)
- Restlessness, aggression, muscle tremors, salivation, teeth grinding, colic, bloat, rumen stasis, sternal recumbency while standing on the hind limbs, convulsions, and death w/in 1-2 hours
- Usually no diarrhea
Lesions of NPN toxicosis?
- No characteristic lesions
- Main lesions due to vascular damage
- Congestion and degeneration in liver and kidney
- Ammonia odor
- Usually dead animals are extremely bloated
Laboratory diagnosis?
- Analysis of feed for urea content
- Analysis of ammonia in whole blood, rumen fluid, and vitreous fluid (depends on the lab)
- The specimens (except blood) should be frozen immediately
- Elevated rumen pH (7.5 or more)
- Blood chemistry
Diagnosis?
- History of exposure
- Clinical signs
- Ammonia odor
- Lab diagnosis
DDx?
- Agents which cause colic such as caustics or inorganic arsenic
- Lead
- Metaldehyde
- Chlorinated hydrocarbon pesticides
- Organophosphates
- Grain engorgement, nitrate poisoning, enterotoxemia and cyanide poisoning
How can you differentiate NPN toxicosis from agents that cause colic such as caustics or inorganic arsenic?
Caustics/inorganic arsenic generally cause diarrhea (often bloody) and no nervous signs
Difference between NPN toxicosis signs and signs of lead, metaldehyde, or chlorinated hydrocarbon pesticide poisonings?
No abnormal posturing, jumping over objects and maniacle behavior in urea poisoning as in chlorinated hydrocarbon poisoning
How can you differentiate between NPN toxicosis and organophosphate toxicosis?
Organophosphates cause parasympathomimetic signs and respond to atropine therapy
What is done to distinguish NPN toxicosis from grain engorgement, nitrate poisoning, enterotoxemia, or cyanide poisoning?
Differentiated by necropsy and lab tests
NPN toxicosis treatment?
- Bloat should be relieved first
- Acetic acid 5% or vinegar to cattle (2-6L) or sheep and goats (0.5-1.0L) followed by a large volume of water
- Treatment should be repeated every 4-5hrs for 48hrs
- Normal saline for dehydration
- Sodium bicarbonate IV for acidosis
- Rumenotomy
