Issue No. 14, Article 2/July 6, 2012
Using Drought-Damaged Corn as Livestock Feed
High temperatures and sustained drought, especially in extreme southern Illinois, have severe damaged many cornfields, with little likelihood of their producing economic grain yields. Producers wanting to salvage this drought-damaged corn for livestock feed should do so very carefully because of the potential for high nitrate levels in the forage. Levels will be highest in fields that received high nitrogen fertilizer or manure applications and in plants that are severely stunted and did not form an ear.
Nitrate concentrations are highest in the lower third of the stalk, so harvesting or grazing only the upper two-thirds of the plant will greatly reduce the potential for nitrate toxicity. Forages containing high levels of nitrate might still be safely fed if they are diluted with grain or other feedstuffs low in nitrate. Within limits, animals can be conditioned to consume high-nitrate forages as long as they are introduced to them slowly, allowing them to acclimate to the high nitrate levels.
Drought-damaged corn that is going to be green-chopped and fed should be tested prior to harvest. Animals should be limit-fed and introduced to the forage slowly. Making hay from drought-damaged corn will not reduce nitrate levels, and any such hay should be tested before feeding.
Ensiling the forage will potentially reduce nitrate levels 30% to 60%. Since fermentation may take up to 21 days, silage should not be fed for at least three weeks after being put into the silo or bag. Care should be taken when ensiling high-nitrate forages because of the potential for production of nitrogen oxide silo gases, which are toxic. Given the variability of nitrate reduction during the ensiling process, silage made from high-nitrate forages should still be tested before it is fed.
Forage testing laboratories may report their findings in a variety of ways: as percent NO3, parts per million NO3, percent NO3-N, or parts per million NO3-N. To add to the confusion, they may report results on a dry matter basis or "as is" moisture. Test levels based on as-is moisture will always be higher when converted to a 100% dry matter basis. Recommended safe feeding levels, which may vary from state to state, are usually given as a range. (See Table 1 for feeding recommendations.) Any results based on as-is moisture must be converted to dry matter basis for the sake of consistency.
Table 1. Guidelines for feeding forages to cattle based on NO3-N and NO3 concentrations (dry matter basis).
Limit feed to 50% or less of ration dry matter.
Limit feed to 25% or less of ration dry matter. Don't feed to pregnant cattle.
Don't feed-potentially toxic.
Finally, some areas of the state received scattered rainfall this week. Harvest of drought-damaged forage should be delayed at least five days after rain. Immediately after rainfall, there is a rapid uptake of nitrate by the plants. Waiting a few days will let plants metabolize the nitrate, reducing the concentration.--Robert C. Bellm