Harvesting and feeding drought stressed corn silage can be a challenge, but for many producers it is it is an absolute necessity, following this year’s mid-season drought. Dairy producers need forage fiber for their herd’s diet.
In most cases, harvesting corn silage from plants that produced little to no grain is still a cost effective way to feed the animals. Ensiling drought stressed corn silage is the best way to reduce potentially toxic nitrates that accumulate in the plant. Nitrate levels can be reduced 20-66 percent by ensiling.
Additionally, harvesting corn 12 inches above the ground will reduce nitrates in the harvested feed, although this will reduce total forage yield (see Table 1 below). Nitrates accumulate in the plant if nitrogen fertilizers (or manure) were used and if there is an interference of normal plant growth, such as drought conditions.
In addition, rain on drought stressed corn will cause the plant to quickly take up any nitrates that were left in the soil. When the plant is harvested and fed, ruminants such as dairy cattle, reduce the nitrates to nitrites which are absorbed and cause a decreased ability of the blood to carry oxygen. Symptoms of nitrate toxicity include increased pulse rate, labored breathing, staggered gate, trembling, weakness, blindness, and death.
It is essential to test corn silage nitrate levels before feeding. Most commercial laboratories offer nitrate testing for $15/sample or less. Laboratories may report nitrates a few different ways. The equations below can be used to convert to nitrate nitrogen:
Nitrate (NO3) x 0.23 = nitrate nitrogen
Potassium Nitrate (KNO3) x 0.14 = nitrate nitrogen
Sodium Nitrate (NaNO3) x 0.16 = nitrate nitrogen
Feeding guidelines for dairy cattle is to keep nitrate levels below 0.4 percent of the total ration and to be extra cautious with pregnant animals. More specific feeding guides for nitrate nitrogen containing feeds are listed in Table 2.
If ensiling drought stressed corn silage in upright silos, be extra cautious about the nitrogen dioxide produced during fermentation. Nitrogen dioxide will be produced within 2 hours of ensiling the feed and can remain for 2-3 weeks. Concentrations as low as 25 ppm are invisible, odorless and toxic to humans. At higher concentrations, the gas is yellowish brown and smells like bleach.
If it is necessary to enter a silo before 3 weeks of fermentation, run the blower fan for at least 30 minutes prior to entry and leave it running while inside. Using a self-contained breathing apparatus is highly recommended.