STRAIGHT FROM THE HORSES MOUTH

Duane A. Lienemann,
 UNL Extension Educator,
Webster County
November 3, 2012 Edition

I have been hearing stories of some losses of cattle in dryland corn stalks and particularly on pivot corners from nitrate poisoning. While this is definitely something I have been worried about, I thought perhaps that we might avoid the problem, especially if producers tested the stalks prior to grazing. With drought, like we experienced this whole growing season, we find that corn and sorghum tend to accumulate high levels of nitrate in the lower leaves and stalk of the plant. The accumulation happens because the plant assimilation of these nitrates into amino acids is slowed by the lack of water, a crucial component to numerous plant processes. You only have to think a little while on that one!
Nitrate toxicity in livestock occurs because animals absorb the nitrates into the bloodstream where it binds to hemoglobin, rendering the hemoglobin unable to carry oxygen throughout the body. The result is eventual asphyxiation and death for the animal. Because of that, it is wise for producers to test their drought-stricken forage prior to grazing or feeding. If any of your harvested forage is high in nitrate, blending the feed with another forage, such as prairie hay or brome, will dilute the total nitrates in the animal’s diet and could potentially reduce the risk of poisoning.
Corn silage - I know that many South Central Nebraska farmers put up their corn as silage earlier this season. That was a great idea as high-nitrate forages chopped for silage and properly ensiled are a safer option for livestock feeding. During the ensiling process, normally the rule of thumb says that 50 percent of the nitrates in the forage will be metabolized by the microbes, which can vastly reduce the risk of poisoning. However, it is still good to test silage for nitrates before feeding. Silage can still contain toxic levels if the initial level was very high. Nitrates are reduced during ensiling however the reduction can range from 20-80%, however forage that was dry going into the silage pile may only have a 20% reduction.
Crop residues – The rule of thumb is that if an average or better grain yield was harvested, nitrates are less likely to be a problem in the crop residue left behind. However regrowth or volunteer growth in fields where grain production levels were substandard may contain problem levels of nitrate due to excess N fertilizer remaining in the soil. Sample the plant material you expect animals to graze, and in the case of fields with highly variable growth, collect separate samples that represent the different growth and maturity levels attained. Grazing high nitrate forages can be a dangerous practice. Although animals tend to consume the leaves and the top portions of the plant, which contain less nitrates, the risk of consuming a high-nitrate portion of the plant still exists. In addition, the longer the animal is left on a field and the more that animal is forced to eat the remaining forage at the lower portions of the plant, the greater risk of nitrate poisoning. I always suggest to producers that they never turn hungry cattle into stalks. I know it sounds strange, but I think it best to feed your cattle a couple of bales of hay or other feeds before turning them out. You might also want to fence off suspect areas in fields. I also like to add a calcium supplement to the cows' rations when feeding stalks. Corn stalks are high in phosphorous, and extra calcium is necessary to combat mineral imbalances and act as a buffer. Calcium carbonate in the mineral is a good practice.
Baled forages with high nitrates – If you put up corn, milo or even soybean residue, especially from dryland fields or pivot corners into bales, I think it very prudent and wise to test those bales for nitrates. Nitrate concentrations tend to be highly variable within a field --which can be reflected in individual bales, so test accordingly. The same sample that is used for a nitrate test can return information on protein and energy content. Corn baled earlier this summer is likely to be much higher in quality than corn residue baled after grain harvest. Remember however that storage will not decrease the nitrate concentration in baled forage. Applying the forage test information to a plan for feeding is an easy return on investment.
Mixing feeds - High nitrate feeds should be mixed with other feedstuffs to reduce the total nitrate concentration in the diet. Young, pregnant and stressed animals are more susceptible to nitrate toxicity. Make sure to consider nitrates from all components of the diet. This includes the water source. Introduce the high nitrate feed gradually over several days. Avoid situations where a large intake of high nitrate feed may occur in one meal. Over time, animals can adjust to higher levels in the diet. Feeding smaller amounts several times a day can be used to adapt cattle to nitrates. If grazing, gradually increase hours of access to the high nitrate feed. A few pounds of grain (2-5 lbs) in the ration will dilute the nitrate in the total ration and provide the carbohydrates for bacteria to quickly convert the nitrogen into ammonia. Mixing of the ration should be thorough enough so that one animal does not have the opportunity to over consume the high nitrate component
Fall cereal grains and cover crops - Wheat, rye, triticale and oats can accumulate nitrates. Test results have shown high nitrates this fall, and forages should not be grazed without testing for nitrates. This would include those that overwinter and might be grazed or hayed in the spring. Green forages generally provide the needed Vitamin A for cattle diets, however animal stores can be depleted in two to six months. High nitrates in feedstuffs may increase the requirement for Vitamin A. Given these considerations, providing supplemental vitamin A makes good sense and is not expensive to do.
I believe that high nitrates will continue to be a concern for livestock producers as they deal with limited feed supplies over the fall and winter. Incorporating high nitrate feeds into cattle diets can be done, but it will require good management and attention to details. My best advice…keep an eye on your animals this year! I like my cattle standing on all four legs.

The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu   or go to the website at: http://www.webster.unl.edu/home