August 2009 Issue



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Toxic levels of nitrates may be found in common pasture grasses and plants during periods of rapid growth, particularly when warm rains follow a very dry summer. Soluble sugars are low under such conditions, so the nitrates that accumulate in the rumen slow the rate of metabolism into ammonia. Drought conditions increase nitrate concentrations in plants and grasses. Crops grown on fallow land often have a higher concentration of nitrates than land which has been in continuous production because plants and grasses absorb nitrates as they grow. High levels of nitrogen in soil can produce high nitrate levels in plants.

Nitrate poisoning is often seen during cooler weather because temperatures below 55* Farenheit slow plant growth and permit nitrate accumulation. However, under 55*F temperature is not required for nitrate poisoning to occur. Goats fed even a small amount of processed grains as part of their diets can survive a higher level of nitrates than animals maintained on pasture alone. The soluble carbohydrates in processed grains allow metabolism of nitrates without harming the goats. When conditions favor high nitrate levels in plants and grasses, producers should consider some grain and hay supplementation as a preventative measure.

Nitrate poisoning usually occurs within several days after hay or plant materials have been moistened by rain, snow, or periods of heavy dampness. Plants containing more than 1.5% dry weight potassium nitrate are lethal to goats. The amount and type of fertilizer used on a field, as well as soil type, influence nitrate accumulation. Conditions such as rapid plant growth on cloudy days allow accumulation of nitrates in forages. Nitrates can be high in hays as well as fresh pastures if they are harvested when nitrates are high in the forage.

Nitrate accumulating plants and grasses include but are not limited to Johnson grass, pigweed, redroot, lamb's quarter, Canada thistle, jimsonweed, cockspur, silver leaf, poverty weed, white ragweed, wild sunflower, fireweed, cheeseweed, sweet clover, Russian thistle, oats, beets, rape, soybean, flax, sudangrass, wheat, barley, and corn. The wise producer will learn the plants, grasses, and soil types on his property.

Nitrate poisoning can be as quick and deadly as prussic acid poisoning. The goat producer needs veterinary help immediately. The first sign of illness is usually difficulty breathing. Mouth breathing, weak and rapid heartbeat, low body temperature, extreme apprehension, anxious behavior, muscular weakness, and foaming at the mouth are symptomatic of this illness -- vague and generalized enough to be confused with many other illnesses.

A visible difference with nitrate poisoning is that the goat's blood is chocolate brown in color. Oxygen cannot get to cells because the normal process in the rumen is altered from the following:

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Normally nitrate converts to nitrite which converts to ammonia then to amino acids then to protein. But nitrate converts to nitrite faster than nitrite converts to ammonia, producing an oversupply of nitrite that changes oxygen-carrying hemoglobin to methemoglobin that does not carry oxygen efficiently. Oxygen never gets to the cells, so the goat dies from lack of oxygen. Blue mucous membranes (including a bluish coloration of the gums) indicating a lack of oxygen, frequent urination, and dilated and bloodshot eyes are symptoms that distinguish nitrate poisoning from other types of toxicity. Death usually occurs within three to four hours. In extreme cases, the goat will die of convulsions within an hour.

Goats that survive nitrate toxicity may have recurring health problems associated with this poison. Interstitial pneumonia and labored respiratory distress often occur. Pregnant does that survive will usually abort within 10 to 14 days from exposure to nitrate poisoning.

Notice the similarities in symptoms and quick death to prussic acid (cyanide) poisoning. The person treating the goat has to know the toxin involved in order to use appropriate medications to counteract the different chemical reactions that distinguish nitrate poisoning from cyanide toxicity.

Nitrate poisoning has caused goat deaths in certain areas of the Great Plains of the United States of America where shallow water wells exist. Nitrate concentrations higher than normal in these shallow wells occur, often during freezing weather, possibly due to ground water contamination from heavily-fertilized soil or barnyard runoff.

Veterinarians treat nitrate poisoning with IV (intravenous) administration of methylene blue. This is not something that the average goat producer can do. So once again, prevention is the key. Preventative measures include:

1) No silage. No wet hay or grain. Although not all silage is high in nitrates, it is a difficult product to feed properly to goats. Silage improperly prepared, stored, and fed can and does mold. Mold can kill goats.

2) Feed a small amount of commercially-prepared feed before allowing the goats onto pasture that might be ripe for developing nitrate poisoning. Keep quality hay available free choice.

3) Avoid grazing/foraging/browsing plants and grasses that have been stressed by climate conditions.

4) Regularly rotate pastures to avoid plant stress.

Suzanne W. Gasparotto

ONION CREEK RANCH Lohn, Texas 8-11-09

My thanks to Kent Mills, goat nutritionist at HiPro Feeds in Texas for fact-checking these articles as they relate to nutritional issues and to Dr. Johnny Needham of the Coleman Texas Vet Clinic for making sure that I properly described symptoms and possible treatment protocols.

Nitrate Poisoning: Hemoglobin that carries oxygen in the blood is replaced by nitrates, which cannot carry oxygen. The goat dies from lack of oxygen in its body's cells. Lack of oxygen explains the chocolate-colored blood.

Prussic acid (cyanide) Poisoning: Hydrocyanic acid prevents release of oxygen in the blood; the goat dies from lack of oxygen in its cells.The blood stays red because oxygen is still in the blood.



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