One dilemma in diagnosing nitrate/nitrite-induced abortions in foals is the lack of well-established normal reference ranges for ocular fluid (eyeball fluid) nitrate/nitrite concentrations. The purpose of the study reported here was to establish a normal reference range for these concentrations in aborted, stillborn, and neonatal foals that died in Central Kentucky.

In cattle, excessive nitrate or nitrite exposure can lead to poisoning and subsequent abortions in pregnant animals. Nitrate/nitrite poisoning is caused by ingesting large amounts of nitrate or nitrite in heavily fertilized forages or nitrate-accumulating weeds, consuming nitrate-containing fertilizers, or ingesting nitrate/nitrite contaminated water.

Nitrate/nitrite poisoning is fairly common in cattle and is always a consideration when abortions occur. To determine if a bovine abortion is the result of excessive nitrate/nitrite exposure, a veterinarian can test the fetal ocular fluid for nitrate/nitrite concentrations. Some nitrate is present naturally in cattle’s ocular fluid, as nitrate is a natural component of the plants they eat. Normal fetal and neonatal ocular fluid nitrate concentrations in cattle can extend up to 25 ppm (parts per million); concentrations greater than this can be associated with nitrate-induced abortions. Nitrite is normally not present in ocular fluid unless bacterial conversion of nitrate to nitrite has occurred postmortem.

In horses, nitrate/nitrite poisoning is very rare and related abortions are even less frequently reported. Some studies indicate that pregnant mares can safely ingest forages with at least twice the amount of nitrate that can cause acute poisoning and death in cattle, with no adverse effects or abortions. However, exposure to extremely high concentrations of nitrate or nitrite in forages or contaminated water could potentially cause abortion