This summer's rainfall pattern has been very sporadic. In some areas, we have had rainfall, and in other areas, droughty conditions have been the norm. In this type of weather, we frequently experience areas of pastures and hayfields that have high nitrate levels. Droughty periods during the summer reduce the ability of grasses to utilize nitrogen for growth so high levels accumulate in the plant. Other weather patterns such as cool, cloudy conditions may have the same effect.
Grasses become toxic to livestock if nitrate levels accumulate high enough.
Some plants are more likely to accumulate nitrates than others such as: sudan grass, sorghum-sudan hybrids, pearl millet (and other millets), bermudagrass and bahiagrass.
Plants that contain high nitrate levels can be fatal to livestock. Nitrates are reduced to nitrites in the animal. Nitrites then oxidize the iron in the blood hemoglobin which prevents oxygen transport from the lungs to the muscles and brain. The animals begin to show symptoms of nitrate poisoning (staggering, disorientation, breathing difficulties, bluish eyes, mouth). Treatments are available, but it is best to avoid situations that may lead to nitrate toxicity.
Problems can occur with heavily fertilized hay made during droughty periods. Hay containing 2500 ppm or less is safe to feed. If growers suspect their hay to have high levels, samples should be sent to a lab for analysis. If the samples contain high nitrate levels, cattle may still eat it, but in diluted quantities. Hay can be ground and fed as mixed feed or diluted with other feed sources. Hay with high levels could be sold for mulch to landscapers. Pasture grasses with high levels should be controlled grazed.
It is important that growers are aware of the potential nitrate problem in our summer grasses. When high levels of nitrates are suspected, test hay or grass and take appropriate precaution to deal with hay or grass that poses a threat to animal health.