By Taylor Grussing
Drought poses many challenges to the beef cow herd. Finding extra forage to graze is one thing producers can do to extend their grazing resources. Failed annual forages such as wheat, may be an option to graze but this forage resource needs to be carefully managed before sending cows out. This is due to the amount of nitrates that could be in the forage and becomes a challenge that producers need to be aware of, especially in the reproductive herd.
Nitrates can be found in multiple forages and weeds, such as wheat, oats, millet, corn, sorghum, sudan, kochia, pigweed, lambsquarter, brome grass and orchard grass, to name a few. Note some of these weeds and grasses in pastures can be just as dangerous and high in nitrates when drought persists. The level of nitrates in a plant is dependent on stage of maturity, soil nitrate level, amount of sunlight/shade, fertilizer application and the part of the plant consumed (lowest 1/3 of the stem will contain the highest level of nitrate).
Nitrate poisoning can be lethal at high enough levels. Essentially what occurs is when forages high in nitrate are fed to livestock, they are converted to nitrite in the rumen. At high enough levels, nitrite, the toxic compound, is absorbed into the blood and causes decreased oxygen carrying capacity throughout the body. With enough nitrates, the oxygen carrying capacity of the animal decreases and can be lethal if not immediately removed from the nitrate source.
When considering grazing pregnant females, it’s important to understand that grazing management is critical to avoid nitrate toxicity and potential abortions. If levels of nitrates become high enough, oxygen to the fetus decreases and early abortions can occur. With the highest concentration of nitrate occurring in the lowest 1/3 of the plant, do not force cows to graze more than the leaves and upper stalks. By grazing only the leaves and upper stalks, this will reduce the inflow of nitrates, because animals are allowed to be selective and will consume the higher quality and more-palatable leaf material prior to the lower portion of the plant.
Source : sdstate.edu