Nitrate and Nitrite Poisoning

Question 1

What enzyme converts Nitrate (NO3) to Nitrite (NO2)? Where does this occur?

Answer 1

Nitrate reductase

occurs in the plant, soil, rumen, or blood

Question 2

what is Nitrite converted to?

Answer 2

Ammonia (NH3)

Question 3

When the rate of nitrate to nitrite is reduced, with continuation of nitrate uptake from the soil, this leads to accumulation of…..

Answer 3

Nitrate in the plant

Question 4

What plant factors will favor nitrate accumulation?

Answer 4

1. Plant species (Sweet clover, alfalfa, wheat, corn, edible plants)
2. Content and form of nitrogen in the soil (Nitrate and ammonia)
3. Plant age - young and immature plants are more toxic

Question 5

What soil conditions will increase nitrate uptake?

Answer 5

rains or moisture, acidic soil, low molybdenum, sulfur or phos, low soil temp, soil aeration and drought

Question 6

T/F: Decreased light reduces activity of nitrate reductase

Answer 6

TRUE

Question 7

What herbicides will increase the risk of ingesting nitrate accumulating plants? why?

Answer 7

Phenoxy acetic acid herbicides bc they increase the palatability of plants

Question 8

What plant parts have the highest accumulation of nitrate?

Answer 8

The stalks (closest to the ground) = the most

Leaves contain less than stalks or stems
The seed (grain) and flower contain little to none

Question 9

T/F: More mature plants have higher concentrations of nitrates

Answer 9

FALSE

younger = higher nitrate

Question 10

T/F: Nitrate is toxic

Answer 10

False

it is not toxic until it is transformed into nitrite

Question 11

What plants are nitrate accumulators?

Answer 11

Pigweed (amaranthus retroflexus)
Oats (avena sativa)
Beets (beta vulgarius)
Johnson grass, sudan grass, milo
Corn (Zea mays)
Lamb's quaters (Chenopodium album)
Sweet clover (Melilotus spp)
Alfalfa (medicago sativa)
Wheat
Sunflower (helianthus annuus)

Question 12

What is sodium nitrate IV used as?

Answer 12

Vasodilator

horses are very sensitive

Question 13

What sources are animals exposed to that they can get nitrate poisoning?

Answer 13

Rapid ingestion of forages or hays containing high amounts of nitrate

Accidental ingestion of feeds or water contaminated with nitrate

overdose with nitrate IV - HORSES ARE VERY SENSITIVE

Question 14

T/F: Nitrates are water soluble

Answer 14

TRUE

Question 15

Are nitrate fertilizers palatable to animals?

Answer 15

YES bc they’re salty

Question 16

What is the toxicity of nitrate poisoning in ruminants?

Answer 16

Slightly toxic

500mg/kg - 1000mg/kg

Question 17

T/F: Ruminants exposed to nitrate may develop a tolerance over time

Answer 17

TRUE

Question 18

Forage greater than ___% may cause acute nitrate toxicosis in ruminants

Answer 18

1%

Question 19

Why are ruminants the most susceptible to nitrate poisoning?

Answer 19

Because the conversion of nitrate to toxic nitrite occurs rapidly in the rumen due to the microflora and nitrate reductase

Question 20

What animals are resistant to nitrate poisoning?

Answer 20

PIGS

Question 21

What is the time frame of nitrate poisoning?

Answer 21

Can be acute OR chronic

***acute is MOST COMMON

Question 22

What animals are most susceptible to nitrate poisoning?

Answer 22

Ruminants - more specifically young adults

3 months - 1 year of age

**prior to 3 months the rumen is not mature - so these animals are not actively converting nitrate to nitrite

Question 23

What concurrent disease will increase nitrate toxicity?

Answer 23

Methemoglobinemia and anemia

Question 24

what reaction is slower; nitrate to nitrite, or nitrite to ammonia?

Why is this important?

Answer 24

The rate of conversion of nitrite to ammonia is slower than nitrate to nitrite… this leads to an excess of nitrite that will be absorbed into the bloodstream

Question 25

T/F: Nitrite will cross the placental barrier

Answer 25

TRUE

can enter fetal RBCs - they are more sensitive, then cause abortion

Question 26

What is the half life of nitrate and nitrite? Why is that important?

Answer 26

The half life of nitrite is very short (less than 1 hour)

Nitrate half life ranges from 4-48 hours - so although it is less toxic - it is better to test for

Question 27

What is the MOA of acute nitrate toxicosis?

Answer 27

Nitrite will react with hemoglobin –> oxidation of ferrous iron to ferric and conversion of hemoglobin to methemoglobin

Blood will be brown-yellow

Question 28

What clinical signs are associated with acute nitrate toxicosis?

Answer 28

Signs of anemia and metheomglobinemia (30min - 4 hours)

• anoxia, vasodilation, hypotension
• patients may just die rapidly with no clinical signs
• rapid breathing, restlessness, dyspnea, weakness, ataxia, sternal recumbency, cyanosis, convulsions, death within a day for a few hours

Question 29

What lesions are associated with nitrate poisoning?

Answer 29

Congested organs due to vasodilation

brown color of blood

Question 30

What clinical signs are noted in chronic nitrate poisoning?

Answer 30

Abortion due to decreased progesterone

Question 31

What is the specimen of choice for nitrate chemical testing if the patient died several hours ago?

Answer 31

Ocular fluid

greater than 30ppm indicated excessive exposure

*serum, plasma, urine, and rumen contents can be tested for nitrate but they are unstable after death

Question 32

What is a good indicator of prognosis for nitrate toxicosis?

Answer 32

Methemoglobin concentration

animals usually die before treatment can be initiated

Question 33

What is a test for nitrates in forage that can be done?

Answer 33

Diphenylamine test: qualitative test for nitrate in forages, rumen contents, and water

positive results indicated by 5000ppm nitrates or more

*dark blue color will indicate a positive result - positive specimens should be sent to the lab for a quantative analysis

Question 34

What is the specific treatment for nitrate poisoning?

Answer 34

Methylene blue 1% IV slowly to tx methemoglobinemia

(different dose for cats)

Other: activated charcoal (not very effective), ruminal lavage with cold water, oral ABs (to inhibit microflora/nitrate reductase)