Forage plants and water are common sources of high levels of nitrates. Some of the causes of abnormal accumulation of nitrates in plants are: nitrogen fertilizaton, drought conditions and some herbicidal treatments. Nitrate accumulation also largely depends on the type of plant. Some of the most common grasses that accumulate nitrate are sudan grass, oats, rape, wheat, barley, and corn. Although in the rumen nitrate is readily reduced to nitrite and then to ammonia, the consumption of plant materials with high levels of nitrate will lead to an acute intoxication. This process is closely related to increased concentrations of nitrite in the rumen which leads to the production of methaemoglobin, a substance that interferes with the ability of blood cells to carry oxygen when concentrations reach 30-40% of total hemoglobin concentrations. Some of the clinical signs of nitrate intoxication are abdominal pain , labored breathing, and cyanotic mucous membranes. Increased dietary nitrate, however, induces a change in the bacterial population that leads to an increased tolerance to high nitrate concentrations in the diet. Nitrate reduction in the rumen competes with other essential metabolic reactions such as mathanogenesis, end-product formation, and microbial protein synthesis, and its toxicity reduces growth, causes Vitamin A deficiency, abortion, infertility, and goiter.