Tips for avoiding nitrate poisoning

Under normal circumstances, plants take up nitrogen in the form of nitrate; it is converted to ammonia, which is incorporated into plant protein.
Cattle convert the nitrate from plants to nitrite, which, in turn, is converted to ammonia and used by microbes in the rumen to make protein.
However, with fall comes frost—and with frost comes disrupted plant growth that can lead to nitrate accumulation in the plant and potential toxic effects to livestock.
If not managed correctly, nitrate poisoning can be fatal.
The following is from an article by Alicia Sopatyk, regional livestock specialist with the Saskatchewan Ministry of Agriculture:
After a frost or other growth-disturbing event, plants continue to take up nitrogen in the form of nitrate, but the conversion to ammonia is slowed dramatically.
Cattle consuming nitrate-dense plants continue to convert nitrate to nitrite, but the nitrite-to-ammonia conversion cannot always keep up.
Nitrite accumulates in the bloodstream where it binds to hemoglobin—reducing the oxygen-carrying capacity of the blood, causing asphyxiation and death.
Level of toxicity will depend on the amount of nitrate in the feed, how fast it is consumed, and amount of nitrate from other sources (i.e. water).
If the forage is yet to be cut, first assess the damage on the plant and take the duration and temperature into consideration.
In general, as leaf survival rate goes up, the wait period to cut forages goes down (more viable leaves means the plant can better utilize nitrate in a timely manner).
However, waiting to cut forages may result in a reduction in forage quality.
Since nitrate levels cannot be determined immediately in the field, the focus should be to put up quality feed while recognizing that nitrates may be present and forages should be tested.
Common crops that have the potential to accumulate nitrates include oats, canola, barley, wheat, rye, flax, sorghum, pearl and German millet, corn, and Sudangrass.
Common weeds that have the potential to accumulate nitrates include pigweed, bull thistle, fire weed, lambs quarters, Russian thistle, white ragweed, Canada thistle, kochia, mustards, millet, and smartweed.
Note different plant species have different tolerances for frost. Stored feeds also can have high nitrate levels and should be tested as such.
Consult with a nutritionist before altering your feeding regime or when considering feeding high-nitrate feeds.
Observation is the first step in prevention, diagnosis, and treatment of nitrate poisoning. When high nitrates are suspected, livestock should be removed from the contaminated feed and provided a high-energy feed such as barley.
A veterinarian should be called to confirm a diagnosis and treat affected animals.
Be aware of nitrate risk in your forage and water sources, and test accordingly.