Nitrates accumulate in forages under stress, including drought,
and are potentially poisonous to livestock when consumed in large quantities. 
Nitrates are commonly found in grass forages like:
  • Corn silage
  • Small grains
  • Sudangrass
  • orchardgrass
  • Fescue
Nitrates can reach extreme levels in common weeds including:
  • Pigweed
  • Lambsquarter
  • Ragweed
  • Johnsongrass
Factors that increase nitrate risk include:
  • High nitrogen fertilization
  • Drought followed by a rain event
  • Frost, herbicide applications, and disease


Take special care when sampling for nitrates.

Standing forage



Fresh forages

  • Variability in nitrate levels within a field can be very high
  • Cut at least 15 whole plants taken at random
  • Cut plants at the same height as harvesting equipment
  • Chop plant to at least 1-inch lengths and mix well
  • Sub-sample and submit about 1/2 lb for testing
  • Collect several samples from the silo face or during unloading
  • Mix well and remove about 1/2 lb for testing
  • Is extremely difficult to sample because animals will selectively consume plants
  • If high nitrates are expected, cautious management is recommended
  • Deliver samples directly to the lab or freeze for 24 hours prior to shipping and ship in an insulated container.
  • Fresh forage in a sealed bag will begin to ferment, which reduces the nitrate level of the sample.

Guidelines for the use of feeds with known nitrate content

Nitrate-Nitrogen (NO3-N) ppm
(100% dry basis)




Over 4,000


Safe. A 1,000 pound cow consuming 20 pounds of dry matter would consume about 8 grams of NO3-N or less than 1 gram per 100 pounds of body weight.

Generally safe when fed balanced rations. Best to limit the problem feed to half of the total dry ration for pregnant animals and also be sure water is low in nitrate.

Limit amount to less than half of total dry ration. Be sure ration is well fortified with energy, minerals, and vitamin A.

Potentially toxic - do not feed

Source: University of Wisconsin
References  +