Nitrite is absorbed from the rumen and converts blood hemoglobin to methemoglobin. Methemoglobin cannot transport oxygen to body tissues, so animals die from oxygen insufficiency. The first symptom to appear is a grayish to brownish discoloration of nonpigmented skin and mucous membranes of the mouth, nose, eyes and vulva. This discoloration results from the chocolate-brown color of the blood, a distinct characteristic of nitrate toxicity that persists several hours after death. As the syndrome progresses, a staggering gait, rapid pulse, labored breathing and frequent urination develop, followed by collapse, coma and death.
Symptoms often occur rapidly, within one-half to four hours after ingestion of a toxic dose.
Some animals exhibit symptoms but recover spontaneously and completely. Pregnant animals may abort a few days later. Preventing Nitrate Poisoning Problems with nitrate toxicity can be avoided with proper management of forage and livestock. Nitrate accumulation can be minimized by analyzing soil and using a balanced fertility program consistent with plant needs and moisture conditions. For sorghum hays, split nitrogen into two or three applications, with a maximum of about 50 pounds of actual nitrogen applied per cutting.