Nonprotein Nitrogen (NPN)

Question 1

What is the most commonly used NPN ?

Answer 1

Urea

others: ammonium nitrate, ammonium carbonate, ammonium chloride, and ammonia birate

Question 2

Which NPN is the most toxic?

Answer 2

UREA

it is the most efficient therefore the most economical but also the most toxic

Question 3

T/F: Urea is toxic

Answer 3

FALSE

Urea itself is not toxic

***lethal synthesis of ammonia is the problem

Question 4

What is the MOA of urea toxicosis?

Answer 4

Lethal synthesis of ammonia + lack of energy due to inhibition of the TCA cycle + decreased cellular respiration/tissue damage

Question 5

What is the normal rumen pH? What is the state of ammonia in that pH?

Answer 5

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

Question 6

1 urea molecule will produce ___ equivalents of animal protein

Answer 6

3

(300% protein profit) super efficient

Question 7

What does urea require in the rumen to be transformed into Ammonia + Carbon Dioxide?

Answer 7

Urease from the rumen microflora and water

The ammonia will then be broken down into amino acids to form microbial proteins –> animal proteins

Question 8

What pH will enhance hydrolysis of urea by urease?

Answer 8

Alkaline pH

Urea is basic

Question 9

T/F: Horses are susceptible to NPN toxicosis

Answer 9

TRUE

although cattle are considered the most susceptible since NPN is often used in their feed

Question 10

What is the usual concentration of Urea in cattle feed?

What is the toxic dose?

Answer 10

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

Question 11

What animals are more sensitive to NPN toxicosis?

Answer 11

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

Question 12

T/F: Fasting will increase urea toxicity

Answer 12

TRUE

so will dehydration or low water intake

Question 13

Will feeds rich in urease increase or decrease the toxicity of Urea?

Answer 13

INCREASE

ex: soybeans

Question 14

Will hepatic insufficiency increase or decrease the toxicity of Urea? Why?

Answer 14

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

Question 15

A diet low in energy and protein but high in fiber will ____ urea toxicity

Answer 15

Increase

Question 16

Too much urea and ammonia result in elevation of the rumen pH (up to ______), then ammonia is in the _____ form

Answer 16

pH up to 8-9

ammonia will be in the non ionized form allowing it to be absorbed and have a toxic effect

Question 17

Does non ionized ammonia cross the BBB and placental barrier?

Answer 17

YES

as well as other cell membranes

Too much non ionized ammonia = hyperammonemia

Question 18

What acid-base condition will hyperammonemia cause?

Answer 18

Metabolic acidosis

Increase in anaerobic glycolysis, increase in lactate

Also increased: BG, BUN, K, Phos, PCV

Question 19

what is the usual cause of death associated with Urea toxicosis?

Answer 19

Cardiac failure (hyperkalemia) and respiratory failure (seizures)

Question 20

What clinical signs are associated with Urea toxicosis?

Answer 20

Rapid onset ( 30min - 3 hr)

Restlessness, colic, muscle fasciulations, ataxia, convulsions, teeth grinding/salivation, bloat, rumenal tympany

**no dhr

Death within 1-2 hours

Question 21

T/F: Characteristic lesions of urea toxicosis aid in diagnosis

Answer 21

FALSE

there are no characteristic lesions - death occurs too rapidly

Question 22

What are the main lesions noted with urea toxicosis?

Answer 22

lesions due to vascular damage
Congestion and degeneration of the liver and kidney
Ammonia odor (subjective - not reliable)
Usually dead animals are severely bloated

Question 23

What specimen sample is the most stable PM in a patient that died from urea toxicosis?

Answer 23

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

Question 24

What may be DDX for urea toxicosis?

Answer 24

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

Question 25

What treatment can be used for a patient with urea toxicosis?

Answer 25

Bloat should be relieved first
Acetic acid or vinegar + cold water into the rumen to decrease pH and slow down the urea to ammonia rxn - this needs to be repeated q4-6 hrs

supportive care: IVF, sodium bicarb for acidosis, rumenotomy

Question 26

What is the prognosis for cattle with urea poisoning?

Answer 26

POOR

Question 27

When the liver converts ammonia to urea - what happens to it?

Answer 27

Some will get recycled in the saliva and most will be excreted in the urine

Question 28

Should animals less than 300 lbs have urea added to their food rations?

Answer 28

NO

and animals less than 500 lbs do not tolerate urea well