Nitrate Poisoning in Horses

Fortunately, nitrate/nitrite poisoning is not a common problem in horses. However, due to serious and potentially fatal consequences of nitrate/nitrite poisoning, horse owners should be aware of the condition and understand the risk factors.

Nitrate/nitrite poisoning in animals is caused by ingestion of excessive amounts of nitrate or nitrite from forages or weeds, nitrate containing

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Fortunately, nitrate/nitrite poisoning is not a common problem in horses. However, due to serious and potentially fatal consequences of nitrate/nitrite poisoning, horse owners should be aware of the condition and understand the risk factors.

Nitrate/nitrite poisoning in animals is caused by ingestion of excessive amounts of nitrate or nitrite from forages or weeds, nitrate containing fertilizers, or contaminated water. Ingestion of large amounts of nitrate can cause gastrointestinal irritation, colic, and diarrhea, but the most important consequence is the conversion of nitrate to the more toxic nitrite anion by gastrointestinal microorganisms. Nitrite is absorbed from the gastrointestinal tract into the blood, causing injury to red blood cells and resulting in inability of red cells to carry oxygen. Clinical signs may include difficulty breathing, weakness, tremors, ataxia, rapid heartbeat, grey/blue or brown discoloration of blood and tissues, seizures, and rapid death. Abortion can occur in animals that survive the initial clinical signs.

While nitrate/nitrite poisoning can occur in any species, ruminants are most susceptible, due to efficient conversion of nitrate to nitrite in the rumen. Non-ruminant species such as horses are much less commonly affected because they do not readily convert nitrate to the more toxic nitrite. Conversion of nitrate to nitrite occurs primarily in the large bowel in horses and is roughly one-fourth as efficient as ruminal conversion in cattle. Hence, compared to ruminants, a much larger dosage of nitrate is required to cause clinical signs in horses. However, horses are very sensitive to nitrite. Ingestion of nitrite can occur when nitrates in forages or water have been converted to nitrite by environmental microbes prior to ingestion.

Documented cases of nitrate poisoning in horses are rare. Most cases involve ingestion of nitrate/nitrite-contaminated water, nitrate fertilizer directly, or forage or hay grown in the area of a previous fertilizer spill. A few cases in horses have occurred from ingestion of high nitrate hay that was baled wet or became wet after baling. Nitrate was converted to nitrite by microorganisms in the hay, resulting in direct nitrite ingestion

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