Cattle Producers Warned of Nitrate Poisoning

Friday, July 6, 2018
Cattle grazing on johnsongrass, such as seen in this undated photo, is causing issues in many areas this year due to the conditions.
(U of Arkansas System Division of Agriculture photo by John Jennings)

Nitrate poisoning in cattle is caused by the consumption of an excessive amount of nitrate or nitrite from grazing crops, hay, silage, weeds, fertilizer etc. All plants contain some nitrate, but excessive amounts are likely to occur in forages which have been grown under conditions of excessive fertilization and/or stress. The hot, dry conditions we are currently experiencing are contributing to johnsongrass, and even a few pigweeds, to test positive for high levels of nitrate/nitrite. The buildup of nitrates in soil brought on by excessive fertilization of manure is a common cause of nitrate accumulation in plants. However, plant species and adverse environmental conditions before harvest affect the concentration of nitrates even more than available nitrogen in the soil. Any stress condition which causes an abrupt decrease in plant growth may contribute to plant nitrate accumulation, even with a normal nitrogen supply. Some of those conditions include lack of sunlight, drought and high temperatures, cold temperatures, frost, herbicides, diseases and soil nutrient imbalances. High nitrate levels do not dissipate when hay is cut and remain high even in dry hay.

High nitrates usually occur when forages have been heavily fertilized with nitrogen fertilizer, but can also occur after poultry litter application or in fields with a history of manure application. Plants growing under stressful conditions and those that have received more than 75 pounds nitrogen per acre in one application may contain more toxins. It is difficult to predict how much toxin may be present in the forage. The grass may appear normal in the morning, but can wilt during afternoon heat which increases toxic potential. Wilted plants or drought-damaged sorghums should not be grazed until at least five days have elapsed since a good amount of rain. When cooler weather returns, growers should also be aware that frost damage can also render forages dangerous.

It is difficult to predict how much toxin may be present in the forage. The grass may appear normal in the morning, but can wilt during afternoon heat which increases toxic potential. Many producers believe the white powdery substance commonly seen on johnsongrass stems in late summer is prussic acid residue, but it is only common powdery mildew fungus and is not considered toxic to livestock. Laboratory and field tests can be conducted on fresh forage and on hay for nitrate content.

Producers who want more information, and those who would like for us to come out and test their johnsongrass, or even pigweeds, for nitrate, may call the office in Piggott at 870-598-2246.

The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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