Reproductive problems may also occur due to a nitrate or nitrite induced hormone imbalance, but most are usually not recognized as feed related. Calves affected by nitrate poisoning during the last three months of gestation are usually born one to four weeks premature, and most appear normal but die within 18 to 24 hours of birth. Newborn calves that survive, but are affected by nitrate poisoning, may have convulsions and seizures. Acute poisoning With acute poisoning the signs of poisoning are observed and the animal is in critical condition. Nitrate is rapidly converted to nitrite in the rumen and is immediately absorbed in large amounts into the bloodstream.
Animals can die within a few hours of initial ingestion of a high nitrate feed.
If cattle are fed once a day, maximum methemoglobin levels occur approximately eight hours after feeding. When cattle are fed twice daily, maximum levels occur four to five hours after feeding. The once a day feeding program results in higher total methemoglobin levels than twice a day feeding. With once a day feeding, a larger quantity of feed is consumed at once and a greater amount of nitrate is released from the feed in a short period of time. Animals are often found in a lying position after a short struggle.