Options for drought-stressed corn

By Nathan Winter and Dan Martens, University of Minnesota Extension

Drought-stressed corn silage can have from 75 to 90 percent of the feed value of normal corn silage. Nitrates may be an issue, but don’t write the crop off with out testing. Any corn that has pollinated and stays alive will use any rain to fill grain and that will add to the value of the crop for feed.

Drought-stressed corn silage typically has higher sugar content, less starch, higher crude protein, higher crude fiber and more digestible fiber compared to normal corn silage. Always make ration changes gradually to give rumen microbes a chance to adjust to feed changes. Check with your crop insurance provider before starting any early harvest.

• Nitrates: There is some variation in “safe” levels reported. University of Minnesota Dairy Nutrition Specialist Jim Linn advises that nitrate levels below 3,000 parts per million are safe. At 3,000 to 6,000 parts per million, it is moderately safe if limited to 50 percent of the total diet dry matter or less. Above 9,000 parts per million, it is very toxic and can cause animal death. Fermentation may reduce nitrate levels from 0 to 50 percent. If a fresh cut sample tests above 3,000 parts per million, fermented feed should be tested again so correct feeding decisions can be made.

Nitrates are more likely to be a problem on corn that grew to a somewhat normal height but was not able to set an ear. Nitrates can be higher for a few days after getting a significant rain. Pay attention to this where corn is grazed, chopped for day-to-day feeding or chopped for forage soon after rain.

Nitrates convert to nitrites. Nitrites can be absorbed in the blood stream and bind to hemoglobin to reduce the amount of oxygen carried by the blood. Animals will show signs that they are not getting enough oxygen. Symptoms may include rapid breathing, muscle tremors, lacking coordination, diarrhea, frequent urination, bluish color around nose and mouth, collapse and death. If a nitrate problem is suspected, handle livestock minimally and call the veterinarian.

Grab samples from corn chopped for daily feeding can be taken or mailed to a forage lab such as Stearns DHIA lab in Sauk Centre (320) 352-2028 or Dairyland Lab in Sauk Rapids (320) 240-1737. For $10 to $15, you have an answer with less risk than using livestock as guinea pigs. Sample prior to harvest by cutting 5 to 10 stalks at a height similar to what you would be chopping. Pick stalks that are representative of the field. This can be difficult with the variation we see in some drought-stressed fields. The next challenge is to chop the sample into small pieces that the lab can handle. Call the lab with questions for handling samples.

Nitrate concentration is usually higher in the lower part of the stalk. Cutting the crop higher will reduce the total nitrate concentration. If you will be short of feed, you may want to test before deciding to leave feed in the field without testing.

Nitrates are a form of non-protein nitrogen. Microbes in the rumen can combine some of the nitrogen from nitrates with carbohydrates in the ration to make protein. Lactating dairy cows that are getting more grain in the ration compared to dry cows and heifers may tolerate somewhat elevated nitrate levels better. Ration formulation should be considered accordingly.

• Chopping corn silage for storage: Chopping for storage is not useful until the crop dries to a moisture content that is suitable for storage. This is typically 60 to 65 percent for upright silos, 50 to 60 percent for oxygen limiting silos, 65 to 70 percent for piles and bunkers, and 60 to 70 percent for bags. Past experience counts. If we cut stalks open, we will find more moisture than we’d think based on the appearance of dried up leaves and leaf sheaths that wrap the stalk.

It might be helpful if we could figure out a practical way to uniformly blend dry chopped hay with corn that is too wet to get a mix that is suitable for storage. I haven’t seen it yet. And I wouldn’t risk a whole silo or bag of feed on a process without seeing some trials that indicate a high success rate.

• Chop for daily feeding: To maintain healthy rumen function, chop for each feeding and chop only the amount of feed the animals can eat within a couple of hours. So provide plenty of bunk space. Wet chopped corn will heat faster. Nitrates convert to nitrites as the feed heats. Other spoilage organisms can become a problem with heating. To keep animals healthy, DO NOT chop enough in a box to feed from all day or for 2 to 3 days. Feed some palatable hay as part of the total ration and balance rations appropriately. That makes more work, but the primary goal is healthy livestock.

• Grazing: Once again feed some palatable hay and balance rations adequately. Grazing saves the cost of fuel and operating chopping equipment. Where possible, use an electric wire or other means to limit access and minimize waste. This may be more feasible with short corn.

• Baling: Technically you could lay corn in a swath and let it dry. There are some challenges. Even if run through a conditioner, it can take a long time for wet stalks to dry. Stalks in a swath can start to spoil before they are dry enough to bale. Stiff stalks could make baleage wrapping a challenge by poking through the plastic wrap. It can be difficult to pick up corn swaths that lay between corn rows with out raking through a lot of soil also. Nitrates do not disappear as corn dries.

• Molds, mycotoxins, and smut: We expect more smut in corn stressed by drought or by other problems. Corn smut by itself is not a health issue for livestock. As the crop deteriorates, other decaying molds can be come a problem. In 2006, while waiting for the crop to dry for chopping, rain came that promoted decaying molds to be more of problem. I would not expect this to be a problem at this point in time. There are tests for molds and mycotoxins.

A wide range articles on drought and heat related to crops, livestock, the home landscape and other topics is posted at the U of M Extension Web site: www.extension.umn.edu. Look for the drought topic in the middle of the home page. University of Nebraska has a good article on “Drought-stressed Corn” that was used for part of this article also. You are also welcome to request information on specific topics by calling the County Extension Office in McLeod County at (320) 587-0770 or Meeker County at (320) 693-5275.

(Nathan Winter is an agricultural educator for McLeod and Meeker counties at the University of Minnesota Regional Extension in Hutchinson. Dan Martens is an Extension educator for Stearns, Benton, and Morrison counties.)