Nitrate- and Nitrite-Accumulating Plants

Abstract Ruminants are particularly at risk of acute, fatal nitrate–nitrite poisoning. Microorganisms in the rumen reduce nitrates to nitrites and then to ammonia for microbial growth. Excess intake of nitrates may cause toxic amounts of nitrite to accumulate in the rumen and be absorbed into the blood. Systemic nitrite converts hemoglobin in red blood cells to methemoglobin, which cannot accept or carry oxygen to the tissues. Ruminants graze a variety of forages and weeds that under certain conditions, including excessive fertilization or reduced growth rate, may accumulate nitrate, which may prove toxic to animals that eat a sufficient dose. The causes of reduced growth rate include drought, leaf damage, herbicide, and reduced sunlight. Nitrate and nitrite content of water, forage, and hay must be considered when determining total nitrate intake. Clinical signs, diagnosis, and treatment of nitrate–nitrite poisoning are discussed in this chapter.