Feed and water related toxicants--NPN

Question 1

3 main feed/water-related toxicants?

Answer 1

• Non-protein nitrogen (NPN)
• Ionophore
• Water deprivation–sodium salt

Question 2

Sources of NPN toxicosis?

Answer 2

• 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

Question 3

NPN toxicosis causes liberation of what?

Answer 3

Ammonia

Question 4

One part urea produces what?

Answer 4

About 3 parts protein

Question 5

What does urea by urease (rumen microflora) change to?

Answer 5

Ammonia (NH₃) and CO₂

Question 6

What does ammonia aminate?

Answer 6

Ammonia aminates ketoacids (from soluble carbohydrates) to amino acids

Question 7

In NPN toxicosis, what do amino acids form? What does that then converted to?

Answer 7

Amino acids form bacterial protein, which is then converted to animal protein

Question 8

What enhances hydrolysis of urea by urease?

Answer 8

Alkaline pH (urea is basic)

Question 9

Most susceptible species to urea toxicity?

Answer 9

Ruminants (horses also susceptible)

Question 10

Which is the most toxic of all NPN compounds?

Answer 10

Urea

Question 11

What is the usual urea concentration of the grain and total ration?

Answer 11

• 3% of the grain ration
• 1% of total ration

Question 12

Which animals are more tolerant to NPN?

Answer 12

Animals that are adapted or preconditioned to NPN

Question 13

What are the toxic doses of NPN?

Answer 13

• Toxic dose in not preconditioned/adapted = 0.45g/kg
• Lethal dose in adapted animals = 1-1.5g/kg

Question 14

How do age, fasting, and hydration status affect NPN toxicity?

Answer 14

• Age
  
  • Animals <1 yr are more sensitive
  • Very young animals (3-6wks) are tolerant
• Fasting
  
  • Increases toxicity
• Dehydration or low water intake
  
  • Increases toxicity

Question 15

What are 3 other things that increase NPN toxicity?

Answer 15

• Feeds rich in urease (soybeans)
• Hepatic insufficiency
• Diet low in energy and protein but high in fiber

Question 16

Is all ammonia produced in the rumen toxic?

Answer 16

No–ammonia produced in the rumen at normal pH (5-6.5) is in the ionized form (NH₄⁺) which is not absorbed

Question 17

What does too much urea and ammonia in the rumen result in?

Answer 17

• 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

Question 18

Mechanism of action

Toxicity of urea is due to what?

Answer 18

Ammonia

Question 19

Mechanism of action

What does ammonia inhibit?

Answer 19

Ammonia inhibits the citric acid cycle–> lack of energy and decreased cellular respiration and tissue damage

Question 20

Mechanism of action

What all does NPN toxicity increase?

Answer 20

• Blood ammonia
• Anaerobic glycolysis
• Blood lactate and systemic acidosis
• Blood glucose
• BUN
• Serum potassium and phosphorus
• Transaminases and PCV

Question 21

Mechanism of action

What might be the cause of death with NPN toxicosis?

Answer 21

Cardiac or respiratory failure

Question 22

Clinical signs of NPN toxicosis?

Answer 22

• 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

Question 23

Lesions of NPN toxicosis?

Answer 23

• No characteristic lesions
• Main lesions due to vascular damage
• Congestion and degeneration in liver and kidney
• Ammonia odor
• Usually dead animals are extremely bloated

Question 24

Laboratory diagnosis?

Answer 24

• 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

Question 25

Diagnosis?

Answer 25

• History of exposure
• Clinical signs
• Ammonia odor
• Lab diagnosis

Question 26

DDx?

Answer 26

• Agents which cause colic such as caustics or inorganic arsenic
• Lead
• Metaldehyde
• Chlorinated hydrocarbon pesticides
• Organophosphates
• Grain engorgement, nitrate poisoning, enterotoxemia and cyanide poisoning

Question 27

How can you differentiate NPN toxicosis from agents that cause colic such as caustics or inorganic arsenic?

Answer 27

Caustics/inorganic arsenic generally cause diarrhea (often bloody) and no nervous signs

Question 28

Difference between NPN toxicosis signs and signs of lead, metaldehyde, or chlorinated hydrocarbon pesticide poisonings?

Answer 28

No abnormal posturing, jumping over objects and maniacle behavior in urea poisoning as in chlorinated hydrocarbon poisoning

Question 29

How can you differentiate between NPN toxicosis and organophosphate toxicosis?

Answer 29

Organophosphates cause parasympathomimetic signs and respond to atropine therapy

Question 30

What is done to distinguish NPN toxicosis from grain engorgement, nitrate poisoning, enterotoxemia, or cyanide poisoning?

Answer 30

Differentiated by necropsy and lab tests

Question 31

NPN toxicosis treatment?

Answer 31

• 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