Today on Texas Vet News I am going to talk about nitrate and nitrite poisoning in horses. Fortunately, Dr. Cynthia Gaskill indicates in Equine Disease Quarterly that this poisoning is fairly rare in horses and is much more common in ruminants such as cattle and sheep. The reason is that horses are not very susceptible to nitrates and their bodies do not readily change nitrate to nitrite, which is more toxic. However, ruminants have microorganisms in the digestive tracts that are efficient at changing nitrates to nitrites and so they are more susceptible to nitrate and nitrite poisoning.

Ingestion of large amounts of nitrate in horses usually causes gastrointestinal problems like colic and diarrhea. Nitrate poisoning usually occurs when horses ingest contaminated water, nitrate fertilizer, or hay grown at the site of a fertilizer spill. Nitrates can accumulate in plants depending on the stage of growth, amount of fertilization, and plant stress. Most of the nitrate accumulates in the stalk of the plant, less in the leaves, and very little in the seed. If horses are exposed to nitrite, it is extremely poisonous and causes difficulty breathing, wobbling, seizures and rapid death. Fortunately, the only times horses get exposed to nitrite is when they ingest high-nitrate hay that is baled wet and microorganisms in the hay have changed the nitrate to nitrite. To prevent this problem, never feed moldy or wet hay and do not bale hay when it is wet. Also, never haul water in fertilizer tanks even if they have been washed out.