Monitoring Nitrate Levels In Drought Stressed Forages

Drought has been a major concern for many farmers and ranchers across the country this summer. According to the Aug. 7 U.S. Department of Agriculture (USDA) Drought Monitor, 74.36 percent of the contiguous U.S. is in severe or worse drought conditions and is now considered one of the most devastating droughts experienced in the past 50 years.  The lack of rainfall combined with long periods of record-breaking heat has forced many grain and livestock producers to turn towards chopping silage in order to avoid a complete crop failure this harvest. However, producers need to be aware of the potential risk in the formation of nitrates in grain and other livestock feedstuffs.

Many nutritionists and veterinarians recommend drought stricken crops be tested for nitrates this season before large portions of crops are harvested. Will VanNostran, president and CEO, Mountain States Consulting Inc. says, “An investment of $25 to $100, depending on what is being tested, is a low cost investment when compared to animal losses” and recommends submitting tests to a certified lab to detect these concerns in drought stressed crops and grain.

If crops, such as corn and sorghum, become stunted where growth is abnormal and reduced, the rapid uptake of nitrogen becomes concentrated in plant tissues. Under normal growing conditions nitrogen is converted into plant soluble proteins and amino acids, which primarily occur in plant leaves and are diluted throughout the growing plant. In abnormal growing plants, such as this year’s drought stressed crop, nitrates accumulate and are toxic to livestock. Even worse, nitrate uptake surges after a rainfall on drought stricken crops.

The accumulation of nitrates varies within the plant. However, it is important to remember the lower stalk and stem contain the highest concentration of nitrates. If nitrates are found, VanNostran suggests, “Raising the cutter bar on the corn silage chopper leaving 10-14 inches of stalk in the field.” Nitrates also can be reduced through proper silage fermentation. Research studies show a 30-50 percent decrease in nitrate levels following the completed three month ensiling process, greatly reducing the risk of toxicity. VanNostran adds, “Cut at the recommended and suggested moisture and maturity. Push no more than 6-8 inches at a time and pack to reach a density greater than 15 lb. DM/cubic foot.”

VanNostran suggests gradually introducing cattle to suspect forages over a period of several days and diluting high nitrate corn silage by introducing more feed grain or hay into the ration. “A diluted feed solution is best. Blend contaminated forage with another clean forage source,” he recommends. Nitrate toxicity in ruminants will occur when nitrate is converted to nitrite faster than nitrite is converted to ammonia in the rumen.  Consequently, when higher than normal amounts of nitrate are consumed, an accumulation of nitrite may occur in the rumen.  Nitrite then will be absorbed into the bloodstream and will convert hemoglobin to methemoglobin, which is unable to transport oxygen to tissues.¹ Even if feeding forages with higher nitrate concentrations does not result in the death of the animal from breathing difficulties, it can cause other problems.  For example, reduced milk production, abortion and performance often occur if high nitrate feed is fed as more than 50 percent of the ration on a dry matter basis.²

“Quality forage is paramount for animal health and subsequently animal performance,” states VanNostran. With chopping corn silage in a drought year, producers need to pay extra attention to potential problems caused by toxins in feed.

For more information on where to have drought-damaged corn tested for nitrates visit the National Forage Testing Association website.

Cattle Feeding Guidelines for Forages Containing Varying Levels of Nitrate³

To convert from parts per million (ppm) to percent, move the decimal point four places to the left (i.e. 8800 ppm = 0.88%).
                
 

¹Soure: Undersander, D. Combs D. Shaver R. and Thomas D. Nitrate Poisoning in Cattle, Sheep and Goats, University of Wisconsin-Madison and the Cooperative Extension Service.
²Source: Vough, L.R. Cassel K.E. and Bararo S.M. Causes and Prevention: Nitrate Poisoning in Livestock, 2000. South Dakota State University.
³Source: Sniffen, C.J. and L.E. Chase. 1981. Nitrates in Dairy Rations, Department of Animal Science, Cornell University.

About Will VanNostran
Will VanNostran is president and CEO of Mountain States Consulting, a family-owned and operated dairy nutrition consulting operation based in Clovis, New Mexico. Mountain States Consulting offers nutritional counsel to dairymen, focusing on cow health and longevity. VanNostran’s nutritional consulting approach is based on forage and forage quality. He is certified by the American Registry of Professional Animal Scientists and has 21 years of field consulting experience. VanNostran earned a bachelor’s degree from The Ohio State University in dairy science with a minor in agricultural business, in 1989.