Written by Megan Van Emon, Extension Beef Cattle Specialist, Montana State University
Elevated nitrate concentrations can be found in forages that have been grown under stress, such as severe drought conditions. Nitrate toxicity is caused by animal consuming feeds and water that have elevated levels of nitrate or nitrite. Care should be taken when feeding cattle cereal grains/hay, corn stalks, orchardgrass, and other feeds known to contain high nitrate levels.
Nitrate is not toxic to animals unless consumed in excessive levels. When nitrate is consumed in excessive levels, nitrite poisoning can occur. Normally, forage nitrate is broken down in the rumen to nitrite by microbes, and then to ammonia. The ammonia is used by rumen microbes for protein. However, when nitrate is consumed in elevated levels, nitrite accumulates within the rumen faster than it can be converted to ammonia. The nitrite then enters the small intestine and is absorbed into the bloodstream. The high levels of nitrite in the bloodstream convert hemoglobin to methemoglobin, which cannot carry oxygen, ultimately limiting the body’s oxygen supply.
Acute nitrite poisoning is caused by animals consuming a large amount of high nitrate forage over a short period of time. Chronic nitrite poisoning occurs when animals consume small amounts of high nitrate forage over a long period of time. Chronic nitrate poisoning is only treated by eliminating the consumption of the high nitrate feed or by diluting the high nitrate feed with low nitrate feeds. Acute nitrite poisoning can occur rapidly after consuming high nitrate feeds, in these severe cases, an immediate intravenous injection of methylene blue by a veterinarian may save the affected animal. However, due to the rapid onset of acute poisoning, treatment may not be the best option.
Testing forages to ensure safe levels of nitrates (Table 1) is the most effective way to minimize the potential of nitrite poisoning in livestock.
|Table 1. Effect of nitrate concentration on livestock (100% DM basis).|
|NO3 – N (ppm)||NO3 (ppm)||Comments|
|350-1,130||1,500-5,000||Generally safe for nonpregnant livestock. Potential for early-term abortions or decreased breeding performance. Limit feed to 50% of ration for pregnant animals.|
|1,130-2,260||5,000-10,000||Limit feed to 25-50% of ration for nonpregnant animals. DO NOT FEED TO PREGNANT ANIMALS.|
|>2,260||>10,000||DO NOT FEED.|
|Hibbard et al., 1998|
|0.1% NO3-N = 0.44% NO3 (0.1 x 4.4)|
|0.44% NO3 = 0.1% NO3-N (0.44 x 0.23)|
|0.1% = 1000 ppm|
Diluting high nitrate feeds with low nitrate feeds can reduce the potential for nitrite poisoning by using the following equation (Glunk et al., 2015; MT200205AG):
WL = (WH)*(%H – %B) / (%B – %L)
WL = weight of low nitrate hay required
WH = weight of high nitrate hay
%H = nitrate concentration of high nitrate hay
%B = nitrate concentration needed in final blend
%L = nitrate concentration of low nitrate hay
For nitrate testing, contact your local extension agent. You can also find additional information in the MontGuide, “Nitrate Toxicity of Montana Forages.”