Nitrate and nitrite (FINAL) Flashcards Preview

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Flashcards in Nitrate and nitrite (FINAL) Deck (55)
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1

Explain accumulation of nitrate by plants

  • Nitrate (NO3) is absorbed from the soil by the plant, is converted to nitrite (NO2)
  • Nitrite is converted to ammonia (NH3)
  • Ammonia is converted to amino acids then to vegetable protein
  • Nitrase reductase converts nitrate to nitrite
  • When the rate of nitrate-to-nitrite is reduced, w/ continuation of nitrite uptake from the soil, this leads to nitrate accumulation in the plant

2

What plant species favor nitrate accumulation?

Sweet clover, alfalfa, corn, wheat, etc.

3

What content/form of N in the soil favors nitrate accumulation in plants?

High nitrate or ammonia

4

What are some soil conditions that enhance nitrate uptake?

  • Rains or moisture
  • Acidic soil (low pH)
  • Low soil molybdenum, sulfur, or phosphorus
  • Low soil temp (13 C)
  • Soil aeration or drought

5

T/F: Decreased light reduces activity of nitrate reductase

TRUE

6

T/F: The use of phenoxy acetic acid herbicides can increase nitrate accumulation in plants

TRUE

7

Which plant parts contain the most nitrate?

The stalks contain the highest concentrations

Leaves contain less than stalks or stems

The seed (grain) and flower contain little or no nitrate

8

T/F: Mature plants have higher nitrate than younger plants

FALSE--younger plants have higher nitrate than mature plants

9

Name 10 nitrate-accumulating plants

  1. Pigweed (Amaranthus retroflexus)
  2. Oats (Avena sativa)
  3. Beets (Beta vulgaris)
  4. Johnson grass, sudan grass, milo (Sorghum spp)
  5. Corn, maize (Zea mays)
  6. Lamb's quarters (Chenopodium album)
  7. Sweet clover (Melilotus spp)
  8. Alfalfa (Medicago sativa)
  9. Wheat (Triticum aestivum)
  10. Sunflower (Helianthus annuus

10

What is this?

Pigweed (Amaranthus spp)

 

11

Plant name?

Lamb's quarters (Chenopodium album)

 

12

What is this?

Alfalfa (Medicago sativa)

 

13

What's this?

Sudan grass

14

What plant is this?

Johnson grass

15

What are nitrate/nitrite used for?

  • Fertilizers
  • Sodium nitrite IV is used as a vasodilator

16

Sources of nitrate/nitrite poisoning?

  • Rapid ingestion of forages or hays containing high amounts of nitrate
  • Accidental ingestion of feeds or water contaminated w/ nitrate
  • Overdose w/ nitrite IV

17

Are nitrates soluble in water?

yes

18

T/F: Nitrate fertilizers are salty

TRUE--they're palatable

19

What are nitrates and nitrites sources of (in soil)?

Sources of nitrogen oxide gases

20

What converts nitrate to nitrite?

Nitrate reductase (microflora)

21

What is the LD50 for ruminants?

Approx. 0.5-1 g/kg

22

What forage nitrate level can cause acute toxicosis?

Greater than 1%

23

Can nitrate/nitrite tolerance develop over time?

Yes

24

Which species is most susceptible to nitrate poisoning?

Ruminants (rumen microflora)

25

Which species is resistant to nitrate poisoning?

Pigs

26

Which species is very sensitive to IV nitrite?

Horses

27

T/F: Nitrate is 10x more toxic than nitrite

FALSE--Nitrite is 10x more toxic than nitrate

28

What are the types of nitrate poisoning?

Acute or chronic

(Chronic nitrate poisoning is not common)

29

T/F: Factors that stimulate rumen microflora increase nitrate reductase activity, thus increasing toxicity

TRUE

30

T/F: Young animals are more susceptible than adults

TRUE

(because that's almost always the freakn case)

31

What diseases increase toxicity?

Anemia and methemoglobinemia

32

What is nitrate reduced by/to? What is that then converted to?

Nitrate is reduced by the rumen microflora to nitrite

Nitrite is then converted to ammonia

33

What is ammonia converted to?

Amino acids and microbial proteins

34

T/F: The rate of conversion of nitrite to ammonia is slower than the rate of conversion of nitrate to nitrite

TRUE

35

What does the difference between conversion rates result in?

Accumulation of nitrite in the rumen which is rapidly absorbed

36

What occurs in erythrocytes?

The nitrite ion enters the erythrocytes in exchange for chloride ion

37

Can nitrite cross the placenta?

Yes--it crosses the placenta and enters fetal erythrocytes (fetal hemoglobin is more sensitive)

38

What is the half-life of nitrite?

Nitrite = less than 1 hr in dogs, sheep and ponies

Nitrate = 4-48 hrs

39

What is the mechanism of action in acute toxicosis?

  • 1 molecule of nitrite interacts with 2 molecules of hemoglobin --> oxidation of ferrous iron to ferric and conversion of hemoglobin to methemoglobin
  • Methemoglobin cannot carry oxygen
  • Direct vasodilation and hypotension
  • Abortion due to fetal methemoglobinemia

40

What levels of methemoglobin show clinical signs? When will death occur?

  • Clinical signs of anoxia develop if methemoglobin is 20-40%
  • Death from anoxemia occurs when methemoglobin reaches 80-90%

41

What is the mechanism of action of chronic toxicosis?

Abortion due to decreased progesterone

42

Clinical signs of nitrate/nitrite poisoning?

  • Sudden death w/ no observed signs
  • Signs occur rapidly (w/in 30 min to 4 hr)
  • Rapid breathing
  • Restlessness
  • Apprehension
  • Dyspnea
  • Weakness
  • Ataxia
  • Sternal recumbency
  • Cyanosis
  • Terminal convulsions
  • Death w/in a day or a few hours
  • Abortion (due to fetal anoxia)

43

Lesions?

Congestion in various organs

Brown-chocolate color of blood (methemoglobin)

44

What is used for chemical analysis? 

What about animals that have been dead several hours?

What is best to be used prior to death?

  • Forage, hay, and water for nitrate
  • Ocular fluid is specimen of choice for nitrate in animals dead for several hours (>30ppm indicates excessive exposure)
  • Serum, plasma, urine, and rumen contents can be used for nitrate, but they are unstable after death

45

Methemoglobin concentration for preservation?

One part blood to 20 parts phosphate buffer (pH 6.6)

46

Diagnosis?

  • History, clinical signs of resp signs w/o lung lesions, and methemoglobinemia usually allow presumptive diagnosis
  • Diphenylamine test

47

What is the diphenylamine test? What do positive results indicate?

Qualitative test for nitrate in forages (hay, pasture, silage), rumen contents, and water

+ results indicate >5,000 ppm nitrate

48

How do you perform the diphenylamine test?

  • Mix 0.5g diphenylamine w/ 20mL of distilled water, then bring the total to 100mL w/ concentrated sulfuric acid
  • Carefully put a drop of solution on inner tissue of the plant stem
  • Dark blue color indicates + result
  • Positive specimens have to be sent to the lab for quantitative analysis (false positives possible)

49

DDx (general)?

  • Agents causing methemoglobinemia
  • Agents inhibiting oxygen utilization by tissues
  • Hemolytic agents
  • Carbon monoxide (bright red blood)
  • Cardiac toxicants

50

DDx for agents causing methemoglobnemia?

  • Agents causing methemoglobinemia
    • Nitrate in ruminants
    • Nitrite
    • Copper
    • Acetaminophen in cats

51

DDx for agents inhibiting oxygen utilization by tissues? How can you differentiate between them?

  • Cyanide (bright red blood)
  • Hydrogen sulfide (dark blood)

52

What are some other hemolytic agents?

  • Copper
  • Zinc
  • Naphthalene
  • Bromate
  • Iodate
  • Arsine gas
  • Onion
  • Mustard
  • Red maple
  • Gossypol
  • Snake venoms
  • Others

53

What are some cardiac toxicants?

  • Digitalis
  • Magnesium
  • Calcium
  • Potassium
  • Fluoroacetate in herbivores
  • Others

54

What is the treatment for nitrate/nitrite poisoning?

  • Methylene blue 1% slowly IV for ruminants and monogastrics except cats as a reducing agent (4-30 mg/kg)
  • Activated charcoal
  • Ruminal lavage w/ cold water
  • Oral antibiotics may inhibit rumen microflora and nitrate reductase

55

Prognosis?

Animals usually die before treatment because death is rapid