Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science


Nitrates are absorbed from the soil by plants and serve as a source of nitrogen which is converted into protein and other nitrogen containing compounds. Plants usually contain relatively small amounts of nitrate because it is converted into other nitrogenous compounds rapidly after being absorbed. Under certain conditions some plants may accumulate fairly high concentrations of nitrate. While these high concentrations are not toxic to the plant, animals consuming them may sometimes show symptoms of nitrate toxicity. Nitrate is not very toxic, but it is readily converted into nitrite which causes toxicity. Nitrate is not very toxic, but it is readily converted into nitrite which causes toxicity. While some conversions of nitrate to nitrite may occur in damp forages prior to consumption, most of the conversion probably take place it the animal’s digestive tract. Nitrite converts the hemoglobin in red blood cells to methemoglobin which cannot transport oxygen from the lungs to the tissues. Thus, animals affected with nitrate poisoning show general symptoms of oxygen deficiency. Ruminants are the principal victims of nitrate poisoning because of the large amounts of plant material they eat and the action of rumen microorganisms in reducing nitrate to nitrite. Sheep appear to be less susceptible than cattle, and horses have been known to suffer no ill effects from oak hay that was poisonous to cattle. Swine appear to be afflicted only upon ingestion of nitrite. In recent years there has been an increased interest in the use of relatively high levels of urea in rations for ruminants. This in turn has prompted the postulation that urea, having a metabolite (ammonia) in common with nitrate, might result in a greater accumulation of the toxic nitrite in animals fed rations containing both urea and nitrate. The subject of this thesis is concerned with interactions involving nitrate and other nitrogenous feeds, and the effect of adaptation to various nitrogenous feeds on the susceptibility of sheep to nitrate toxicity.

Library of Congress Subject Headings





South Dakota State University