Nonprotein Nitrogen (NPN) Flashcards
What is the most commonly used NPN ?
Urea
others: ammonium nitrate, ammonium carbonate, ammonium chloride, and ammonia birate
Which NPN is the most toxic?
UREA
it is the most efficient therefore the most economical but also the most toxic
T/F: Urea is toxic
FALSE
Urea itself is not toxic
***lethal synthesis of ammonia is the problem
What is the MOA of urea toxicosis?
Lethal synthesis of ammonia + lack of energy due to inhibition of the TCA cycle + decreased cellular respiration/tissue damage
What is the normal rumen pH? What is the state of ammonia in that pH?
Normal rumen pH = 6.5
ammonia (weak base) will be mostly ionized at that pH - so it is trapped and inactive
When the pH increases (greater than 7)- ammonia will become non ionized and get absorbed –> Toxicosis
1 urea molecule will produce ___ equivalents of animal protein
3
(300% protein profit) super efficient
What does urea require in the rumen to be transformed into Ammonia + Carbon Dioxide?
Urease from the rumen microflora and water
The ammonia will then be broken down into amino acids to form microbial proteins –> animal proteins
What pH will enhance hydrolysis of urea by urease?
Alkaline pH
Urea is basic
T/F: Horses are susceptible to NPN toxicosis
TRUE
although cattle are considered the most susceptible since NPN is often used in their feed
What is the usual concentration of Urea in cattle feed?
What is the toxic dose?
Usual: 3% of the grain ration and 1% of total ration
**Animals adapted to NPN are more tolerant
Toxic: 0.45 g/kg (in non adapted animals)
Lethal dose in adapted animals = 1-1.5 g/kg
Moderately toxic in non adapted animals
Slightly toxic in adapted animals
What animals are more sensitive to NPN toxicosis?
Animals less than one year, greater than 3 months
*very young animals (3-6 weeks) are tolerant since they do not have a developed rumen at that time
T/F: Fasting will increase urea toxicity
TRUE
so will dehydration or low water intake
Will feeds rich in urease increase or decrease the toxicity of Urea?
INCREASE
ex: soybeans
Will hepatic insufficiency increase or decrease the toxicity of Urea? Why?
Increase
If the liver is not fully functional - it will not metabolize ammonia appropriately leading to an accumulation
*the liver SHOULD convert ammonia to urea, which is then excreted in the urine
A diet low in energy and protein but high in fiber will ____ urea toxicity
Increase
Too much urea and ammonia result in elevation of the rumen pH (up to ______), then ammonia is in the _____ form
pH up to 8-9
ammonia will be in the non ionized form allowing it to be absorbed and have a toxic effect
Does non ionized ammonia cross the BBB and placental barrier?
YES
as well as other cell membranes
Too much non ionized ammonia = hyperammonemia
What acid-base condition will hyperammonemia cause?
Metabolic acidosis
Increase in anaerobic glycolysis, increase in lactate
Also increased: BG, BUN, K, Phos, PCV
what is the usual cause of death associated with Urea toxicosis?
Cardiac failure (hyperkalemia) and respiratory failure (seizures)
What clinical signs are associated with Urea toxicosis?
Rapid onset ( 30min - 3 hr)
Restlessness, colic, muscle fasciulations, ataxia, convulsions, teeth grinding/salivation, bloat, rumenal tympany
**no dhr
Death within 1-2 hours
T/F: Characteristic lesions of urea toxicosis aid in diagnosis
FALSE
there are no characteristic lesions - death occurs too rapidly
What are the main lesions noted with urea toxicosis?
lesions due to vascular damage
Congestion and degeneration of the liver and kidney
Ammonia odor (subjective - not reliable)
Usually dead animals are severely bloated
What specimen sample is the most stable PM in a patient that died from urea toxicosis?
Ocular fluids - from the vitreous body
- can also perform urea and ammonia analysis on whole blood, rumen content, and analyze feed
- all specimens besides blood should be frozen immediately
What may be DDX for urea toxicosis?
agents which cause colic such as caustics or inorganic arsenic
but these generally cause DHR and no neuro signs (which is the opposite of Urea tox)
other: lead, metaldehyde, chlorinated hydrocarbon pesticides, organophosphates, nitrate, cyanide
