August 20, 2018
By Kristin Ulmer and Mary Drewnoski
The game of "what-if" can be tricky. What if the corn crop becomes drought-damaged this year? Are you prepared to utilize this corn crop as a forage?
Drought-stressed corn will start to wilt and roll its leaves. If drought occurs for four days during the silking and pollination period — the early reproductive stages of the corn plant — a drop in yield by as much as 40% to 50% can occur. Cattle producers looking to make use of the drought-stressed corn may harvest it for forage, but it should be done with a few considerations.
When harvesting drought-stressed corn to feed, consider these factors:
• Chemical labels. If harvesting corn as forage or grazing directly, check the chemical and pesticide labels applied to crops to ensure the crop is cleared for forage and the minimum preharvest interval (PHI) has been met.
• Nitrate poisoning potential. Drought conditions can prevent normal plant growth, thereby higher levels of nitrates can accumulate in the cornstalk. Nitrates outcompete oxygen in an animal's hemoglobin and can cause suffocation or even lead to death. Livestock do convert nitrate to other nitrogen compounds in the rumen, but it is the amount consumed and the time it took to consume the forage that become the issue. Feedstuffs testing high in nitrates can be used as part of the ration if they are diluted with lower-nitrate feeds. Talk with an Extension educator about what could be blended and what ration could be balanced.
Forage options for drought-stressed corn include:
• Feeding green. Green chop is chopping corn and feeding it fresh instead of first letting it go through an ensiling process. Nitrates accumulate in the lower 8 to 12 inches of the standing cornstalk in drought-challenged corn. Setting the cutter bar higher and chopping the corn for green chop may lower the amount of nitrate fed. If feeding green chop, feed immediately after harvest and only feed the amount that animals will consume in two hours. If green chop is left in the bunk or on the wagon, it can heat up, and nitrate will be converted to nitrite, which is 10 times as toxic as nitrate when fed to animals. So, it's better to feed green chop two to three times a day to ensure it is cleaned up quickly.
Also, ensure plenty of bunk space — about 36 inches of space per cow — so boss cows do not overeat, and timid cows can eat their share. If nitrate poisoning is suspected, remove the contaminated feed from the diet, provide a high-energy feed such as corn grain, and call a veterinarian immediately.
• Feeding as corn silage. The ensiling process reduces nitrate levels by as much as a third to a half, as the gas escapes as nitrous oxide compounds from the pile. Moisture level is key. Excess moisture can lead to poor fermentation or reduced feed value. Proper moisture is 65%, with a range of 62% to 68% moisture. Delay harvest as long as there is some green in leaf and stalk tissue.
Proper ensiling is important. Before using the silage in a ration, it's a good idea to test it for moisture, crude protein, total digestible nutrients (TDN) and nitrate content to allow for a proper formulation in a ration. Tips for obtaining a good sample are provided in the NebGuide, Sampling Feed for Analyses. YouTube videos from the Silage for Beef Cattle Conference will provide more in-depth information on producing and using corn silage in cattle rations.
• Baling corn stover for dry feed. If corn grain is minimal on drought-stressed plants and silage isn't an option, baling corn stover for feed is a final opportunity. Cut the stover at 8 to 10 inches above the ground when some green tissue is present and allow it to dry down to stover for baling.
Nitrates still exist in the corn stover and do not decline as it does in the ensiling process, so use caution when feeding. Sending in a sample before harvest will give an initial look at nitrate levels. If tests come back at a dangerous level, cut the plants higher, at 8 to 12 inches off the ground.
• Grazing drought-stressed ears. If you aren't planning on a mechanical harvest, cattle can graze the drought-stressed corn standing in the field. However, take caution when turning cows out for unlimited access of the field. Seasoned cows will seek out corn ears before forage, meaning the cow will have a high-grain diet and an increased risk of acidosis. Ensure cattle are acclimated by gradually increasing the amount of grain consumed over the course of a week. Cows should not be turned out hungry on drought-stressed corn but fed on low-nitrate forage beforehand. Also, consider feeding high-quality hay as a supplement and then moving to the cornfield for a period during the day.
Cross-fencing and strip-grazing areas will help limit intake and reduce trampling while cattle are turned out on drought-stressed corn. Remember that nitrates are an issue with higher concentrations in the lower portion of the stalk.
Options exist for using drought stressed corn, but producers must look at their specific scenarios to determine which situation would work well with the risk taken. With careful management and care in feeding, there are several options for putting drought-stressed corn to use.
Ulmer is an educator and Drewnoski is a beef systems specialist with Nebraska Extension. This report comes from UNL CropWatch.
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