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Toxicology VAP845 > L14. Bovine Nirtrate Poisoning > Flashcards

L14. Bovine Nirtrate Poisoning Flashcards

1
Q

Nitrate Nitrogen Absorption:

Plants

A

nitrate

Nitrite, urea, ammonia

Gaseous N2 is not available unless the plant possessses nitrogen fixing systems

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2
Q

Nitrate Nitrogen Absorption

A

Nutrate uptake is controlled by 2 systems:

Constitutive, low affinity transport system (LATS)

Inducible, high affinity transport system (HATS)

HATS is ATP dependent

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3
Q

Fate of nitrate in the plant

A
  • To be useful to the plant for protein production, nitrate must first be reduced to ammonium by nitrate reductase (NR) enzymes
    • ammonium is incorporated into amino acids and protien
    • Excess ammonium is converted to ammonia and released into the air
      • NR production is suppressed when there is reduced protein production
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4
Q

Risk factors for nitrate accumulation:

plant species

A

crop grasses, weed grasses, broadleaved annual weeds

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5
Q

Risk factors for nitrate accumulation:

Time of year

A

higher risk during growing season

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6
Q

Risk factors for nitrate accumulation:

High soil nitrogen

A

fertilized fields

Enclosures that previously had high animal densitites

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7
Q

Risk factors for nitrate accumulation:

Environmental conditions that reduce / stop plant growth

A

summer drought

persistent cloudiness or plants growing in shade

Unseasonal hot or cold weather

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8
Q

Nitrate

A

Anything that stunts the growth of hte plant will increase nitrate accumulation in the lower part of the plant

Phenoxy acid derivative herbicides like 2,4-D,a nd 2.4.5 T applied to nitrate accumulating plants during early stages will increase growth and have a high residual in surviving plants

Theses weeds will be eaten even when perviously avoided prior to spraying

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9
Q

Nitrogen

A

For corn:

higher concentration the lower you go

Nitrate levels are not reduced by drying and baling

Ensiling process reduces nitrate ~40-50%

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10
Q

Forage

A

THe difference is in the rate at which nitrate is released in the rumen liquid

On a dry matter basis hay is consumed per kg dry matter much more rapidly than that from fresh forage

Nitrate is released more rapidly form the cells of hay than from fresh forage

The nitrate from fresh gas enters the rumen more gradually and so the absorption of nitrite takes place at lower rates

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11
Q

Effect of summer drought

A
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12
Q

Other sources of nitrate/nitrite

A
  • Contaminated water
    • fertilizers
    • septic tanks
    • Some soils are naturally high in nitrates/nitrites
  • Fertilizer spills, inapporpriate use, or careless storage
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13
Q

Fate of nitrate in the animal

A

Ruminants:

  • nitrate is reduced to nitrite by rumen microbes
    • this is a rapid, high capacity process
  • Nitrite is further reduced to ammonia and released into the air by eructation
    • this is a less efficient process
  • In nitrate production rates are high it accumulates and gets absorbed

Fermenting monogastrics are intermediate in nitrate reducing efficiency

Non-fermenting monogastrics, nitrate reduction is negligible

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14
Q

Toxic effects of nitrate

A

Nitrate salts are mildly irritating

May cuase signs of GI irritation at high concentrations: Salivation, colic, diarrhea, vomiting in some animals

GI irritation may be the the dominant effect in ruminants when rumen mircorbial avitivity is low

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15
Q

Toxic effects of nitrite

A
  • Nitrite oxidizes hemoglobin to methemoglobin
    • when the metHb reductase capacity of RBC’s are overwhelmed, MetHb concentrations rise
  • Increased MetHb reduces the oxygen carrying capacity of blood
    • 30-4-% metHb causes mild clinical signs
    • >70% MetHb causes severe clinical sings and death
  • Fetuses and neonates are most sensitive
    • poisoning can occur in monogastric neonates drinking nitrite contaminated well water
  • Low level, but persistent nitrite exposure is associated with:
    • impaired Vit. A function
    • Endocrine Abnormalities (Thyroid)
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16
Q

Nitrate:

Animals At Risk:

Human infants

A
  • Achlorhydria (low acid production in stomach)
  • Higher bacterial populaitons in gut
  • “blue baby” syndrome
  • Methemoglobiemia
  • Basis for human drinking water standards
    • maximum of 45 ppm NO3
    • equivalent to 10ppm NO3-N
17
Q

Nitrate:

Animals At Risk:

Ruminants

A

Most susceptible

Rumen microflora rapidly converts nitrate

18
Q

Nitrate:

Animals At Risk:

Horses, pigs, dogs, humans

A

are resistant to nitrate

However, all species are susceptible to ingestion of nitrite form non plant sources

19
Q

Clinical Picture:

Acute

A

“typical syndrome”

Signs of hypoxia, weakness, exercise intolerance, tachypnea, collapse, convulsions, death

20
Q

Clinical Picture:

Subacute and Chronic Syndromes

A

Abortions 3=7 days after exposure

weak calves

Decreaed milk production

Decreased feed conversion rates

Increased susceptibility to infections

21
Q

Nitrate - Clinical signs

A

Onset in 30 minutes to several hours

Typical sings include:

weakness

cyanosis of mucous membranes

Ataxia

Collapse

Death

22
Q

Postmortem

A

Brown discoloration of blood and tissues

may take 2-10 minutes to develop on opened carcass surfaces

can be seen on mucous membranes

Brown color disappears after a few hours

Non specific sings of GIT inflammation

Rumen often contian recognizable nitrate-accumulating plants

Late term abortions may be associated with placental necrosis

23
Q

Diagnosis

A

Clinical signs

Brown discoloration of blood and tissues

Submit samples for nitrate analyses

Serum:

good antemortem sample

normal values are about 35% hgher than acqueous humor, but decline rapidly after death

Eyeball or aqueous humor:

Best postmorten sample

nitrates are stable in aqueous humor for 24 hours to 1 week - ship on ice

Adult cattle: >10ppm suspect, >20ppm diagnostic

Neonates/fetuses: 25-50 ppm suspect; >50ppm diagnostic

24
Q

Nitrate - DIagnosis

A

Chocolate brown blood, tissues

Samples to test:

ocular fluid

forage

1% NO3 on dry matter basis is potentially lethal ro ruminants

water, suspect material

Be aware of units used ot report nitrate

Each lab reports differently and your producres won’t know that

1ppm N = 3.3 ppm NO2 = 4.4 ppm NO3

25
Q

Nitrate - clinical repsones

A

Methemoglobin:

Normal = 1-3 %

Clinical sings = 30-40%

Death >80%

MetHb rapidly decays after collection, so diagnostic value is limited

26
Q

In-field Nitrate Testing

A

Diphenylamine and Sulfuric Acid test

27
Q

Treatment:

Acute

A

remove suscpected feed and/or source

Methylene Blue; repeated if necessary

6 month WDI - potential carcinogen

28
Q

Treatment - Subacute Syndrome

A

Injectable or oral vitamin A, D, E

Iodized salts or organic iodine

Feed high quality protein and abundant carbohydrates

29
Q

nitrate concentration of a dry matter basis

A
30
Q

Management

A

TEST SUSPECT FEED BEFORE USE!!

High nitrate feed may be mixed with low nitrate feed to reduce nitrate levles

Feed high qualitiy protein and abundant carbohydrates

requires gradual introduction of higher nitrate feed

feed high quality safe material before first access to suspects feed

Propionibacteria inoculations into the rumen at least 3 weeks prior to exposure

31
Q

Propionibacteria

A

natural rumen microorganisms

Generally recognized as safe

Used industrially

Capable of nitrate and nitrite reduction $16/hd of cows

32
Q

Prevention of nitrate poisoning

A

Know the major sources and circumstances for nitrate risk

Introduce ruminants to high risk forages slowly

Provide readily utilized energy source

Recognize the causes of nitrate accumulation

Toxicology VAP845 (15 decks)

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