Nitrate poisoning

• Nitrate itself is not toxic to animals, but at elevated levels, it can cause a noninfectious disease called nitrite poisoning.

• Nitrate poisoning is generally caused when animals eat too much forage that is high in nitrates not changed to protein in the plant.

• Poisoning can also happen when animals eat too much urea or nitrogen fertilizer spilled in the field or left where the animal scan find it.

• Too much forage that is high in nitrates not changed to protein in the plants.

• Normally Nitrate is broken down to nitrite (NO2) and then to ammonia (NH3), Ammonia is then converted to protein by microbes in the rumen (which is the compartment of the ruminant stomach).

• If Nitrite is absorbed into the blood and combines with hemoglobin to form met-hemoglobin, which causes a reduction in the ability of the blood to carry oxygen from the lungs to body tissues.

• All plants contain some nitrate, but excessively high levels are likely to occur in forages grown under stress conditions.

• Nitrates accumulate in plants only when:

i. A large amount of nitrate in the soil.

ii. Some factor interferes with normal plant growth.

• Plants convert nitrate (NO3) to nitrite (NO2) which in turn is converted to ammonia and then to amino acids, the building blocks of protein.

• During the night, nitrate accumulates when photosynthesis is inactive, then during the day, nitrate is quickly converted to protein.

• In certain conditions, this balance can be disrupted so that the roots will accumulate nitrate faster than the plant can convert the nitrate to protein.

• The highest levels of nitrate accumulate when drought occurs during heavy nitrate uptake by the plant.

• Nitrate nitrogen in 28 samples of drought-stressed corn.

Plant part ppm NO3N1

i. Leaves 64

ii. Ears 17

iii.Upper 1/3 of stalk 153

iv.Middle 1/3 of stalk 803

v. Lower 1/3 of stalk 5,524

vi.Whole plant 9781 ppm = parts per million

• The first symptom to appear is a grayish to brownish discoloration of non pigmented skin and mucous membranes of the mouth, nose, eyes and vulva.

• This discoloration results from the chocolate-brown color of the blood, a distinct characteristic of nitrate toxicity that persists several hours after death.

• As the syndrome progresses, a staggering gait, rapid pulse, labored breathing and frequent urination develop, followed by collapse, coma and death.

• Pregnant animals may abort a few days later.

• Symptoms often occur rapidly, within one-half to four hours after ingestion of a toxic dose. Some animals exhibit symptoms but recover spontaneously and completely.

• Normally nitrate is assimilated so rapidly following absorption from soil that its concentration in plant tissues is low. the most notorious accumulators of nitrate are the sorghums. Other annuals that less frequently accumulate nitrate are small grains.

• Some perennial grasses and weeds ( mustard, nightshade and lamb’s quarters) also can contain dangerous levels. The corn may be safe but weeds harvested with it may be poisonous.

• Accumulation usually is triggered by some environmental stress where plant growth is restricted but absorption of nitrate from soil continues.

• Environment factors includes reduce sunlight, frost, certain herbicides, acid soils, low growing temperatures, and deficiencies of essential nutrients like phosphorus, sulfur and molybdenum.

• When more soil nitrogen is present than needed for maximum growth, some plants tend to accumulate nitrate even without environmental stress. This response is particularly true with hardy soil feeders like sorghum, noted for “luxury consumption” of certain nutrients.

• Death loss from nitrate is an occasional problem in cattle consuming certain annual forages, particularly sorghum hybrids.

• High nitrate forages can be used if diluted with other feedstuffs and supplemented with energy.

• Nitrate toxicity is sometimes a lethal problem for livestock especially during the fall.

• Avoid poisoning with good management practices.• A qualitative check called the diphenylamine test can be

used to screen forages for potential harm.

• Avoid poisoning by routinely testing any forage – pasture, hay or silage – suspected of containing excessive nitrate.

• A qualitative check called the diphenylamine test can be used to screen fodders for potential harm.

• If results of the diphenylamine test are positive, send fodder samples to a laboratory for quantitative analysis.

• When fodder is collected for analysis, it is essential that representative samples be taken. Although samples often are pooled for other laboratory analyses like moisture and protein, nitrate tests often are required on individual bales or from specific areas of a field to accurately assess the potential for toxicity.

• To illustrate this point, an evaluation of 15 large round bales of sorghum hybrid hay from one cutting showed considerable variation from bale to bale, with nitrate levels ranging from 17,500 to 39,000 ppm.

• Testing can be done :i. In field

ii. In Laboratory

Field methods include qualitative spot color methods and some quantitative methods that use colorimeters

and nitrate electrodes.

Purpose

• This technical procedure shall be followed for the preparation of the spot test solutions within the Trace Unit.

Preparationa)Weigh 0.5 gram of diphenylamine.

b)Measure 20 mL of deionized water.

c)Measure 100 mL of sulfuric acid.

d)Combine diphenylamine, deionized water and sulfuric acid.

I. Prepare the test solution by mixing 0.5 grams diphenylamine with 20 milliliters of distilled water, then bringing the total to 100 milliliters with concentrated sulfuric acid.

II. Carefully place a drop of the solution at various locations on the inner tissue of the plant stem; repeat for several stems in each sample.

III. If an intense blue color appears in a few seconds, the fodder contains potentially dangerous levels of nitrate.

IV. If the results are positive (blue color), send the fodder to a laboratory for quantitative analysis before feeding.

V. Occasionally, false positive reactions occur. However, any sample resulting in a positive reaction should be tested in the laboratory.

VI. Avoid contaminating the solution in the bottle with plant tissue or other material. Discard any solution that is not clear.

• Observed clinical signs.

• Possible exposure to toxic plants, feeds or water.

• Post-mortem findings.

• Laboratory tests.

• Nitrate accumulation can be minimized by analyzing soil

• Use of true sudans or sudan-sudan hybrids instead of sorghum-sudan or sorgo-sudan hybrids may be warranted to reduce potential for accumulating nitrate

• Do not ignore differences in yield, quality, drought tolerance and insect and disease resistance.

• Test samples of plants from different areas of the field, particularly those showing the most stress, for nitrate content. If the level is dangerous, delay harvest until rain comes and the plant increases in maturity.

• Silage also may be a good alternative since appreciable reduction in nitrate levels Forages that are high in nitrate will normally lose 40 to 60 percent of their nitrate content during fermentation.

• Urgent veterinary attention is required to confirm the tentative diagnosis and to treat affected animals. Stock should immediately be removed from suspect material, and be handled as little and as quietly as possible. Hay or some other low-nitrate herbage should be fed to dilute the nitrate and/or nitrite in the stomach.

• Affected animals can be treated by intravenous injections of methylene blue, a powdered dye material. Methylene blue converts the methaemoglobin back to oxygen-carrying hemoglobin.

• This matter is under review. Contact your veterinarian for advice. If producers have an old supply of methylene blue on hand, they should consult their veterinarian before attempting to use it.