Nitrate Poisoning – Testing and Prevention

  • Both plants and animals need nitrogen because it is an essential element in building protein.
  • Nitrogen, present in the earth in many forms, can be converted by soil microbes into nitrates, which are soluble and easily taken up by a plant.
  • Nitrates are assimilated into proteins in the roots or stems of plants; however, any event that interrupts this process can lead to an accumulation of nitrates resulting in a potential for acute toxicity.
  • Poisoning is due not directly to nitrates, but to nitrites, which are derived from the consumed nitrates in the rumen, or the caecum of a horse. Nitrites are absorbed into the blood and combine with hemoglobin to form methemoglobin, which can no longer carry oxygen to the body tissues. If too much methemoglobin is produced, the animal will asphyxiate and die. Symptoms of nitrate toxicity mimic those of prussic acid poisoning, except that the blood of an animal that has died from nitrate toxicity will present a characteristic chocolate brown color due to the lack of oxygen.
  • Subacute poisoning can result in reproductive problems including more days open, greater length of time for breed-back, and abortion.
  • Certain environmental factors have to come into play to trigger nitrate accumulation in plants, the number one cause being drought. During periods of drought, low moisture will cause nitrates to concentrate in the soil, yet, at the same time, drought stress tends to slow the conversion of nitrates into protein in the plant, causing an accumulation of nitrates in the stem.
  • Other environmental factors that can interfere with the normal growth of a plant resulting in nitrate accumulation include frost damage, hail damage, and injury from herbicides. Rarely, trace element deficiency can also retard plant growth.
  • Plants most liable to nitrate build-up include oats, barley, wheat, rye, corn, sorghums and sudan grass, and the weeds kochia, thistle, sunflower and pigweed. Young plants are at higher risk than older ones.
  • A laboratory test can determine levels of nitrate in forage and should be included in a good pasture management program.
How to take a forage sample for nitrate analysis
  • For standing forages, create a composite sample of plants taken from 10 areas of the pasture with similar fertility and moisture conditions. Include the lower stem where levels are at their highest. Do not mix plants from ‘good’ and ‘bad’ areas of the field; instead send them as separate samples.
  • Silages should be sampled at several different points taking only unspoiled material
  • Bales should be sampled from several areas using a bale probe, then combined.
  • Place the samples into clean paper bags, and secure the top of the bag. Silage samples should be placed in resealable plastic bags. Clearly identify each sample bag with name, sample type, and date.
  • Promptly bring, or ship, the sample to the Northeast Texas Farmers Co-Op scale house, store or fertilizer plant.

Green-chopping and baling will not reduce nitrate levels if they are high. Ensiling can reduce nitrates, but, under particular conditions, can produce silo gases. For further information on nitrates and pasture management to keep your herd healthy, contact the Northeast Texas Farmers Co-Op.