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. In situations where tests indicate soil is laden with nitrogen, reduce rates accordingly.