Ruminant animals (such as cows and sheep) and infant monogastrics (such as baby pigs and chickens) also have nitrate-converting bacteria in their digestive systems. For this reason, nitrate poisoning affects them the same way it affects human babies. Because adult monogastrics generally do not have nitrate-converting bacteria, they are not affected by methemoglobinemia. Horses, however, are an exception. They are monogastric, but they also have a cecum, which is similar to a rumen. The nitrate-converting bacteria living in the cecum increase the risk of nitrate poisoning.
Livestock are exposed to nitrate in feed as well as in water. Crops harvested after weather stress (such as drought) are especially likely to have high nitrate contents. To protect livestock, fodder can be tested for nitrate before being fed.
The symptoms of nitrate poisoning in animals include a bluish or brownish discoloring of nonpigmented areas (around the mouth and eyes) or mucous membranes, a sluggish, staggering gait, rapid heartbeat, frequent urination, and labored breathing followed by collapse. In severe cases, convulsion and coma may occur, followed by death one to three hours after the first signs appear.
A veterinarian should be contacted as soon as any of these symptoms are noticed. Blood for diagnosis must be drawn while the annual is alive or within two hours after death. Blood from affected annuals will have a chocolate brown color. If the problem is diagnosed in time, animals can be treated and often fully recover. Pregnant animals that recover may abort within a few days.