Chopping Tips for Drought-damaged Corn Silage

How to avoid toxic nitrate levels in stressed-out corn silage.

Published on: Aug 16, 2007

The potential for high nitrate levels in corn silage is high in drought-damaged corn. Make sure the near-term problem doesn't come back to haunt cattle fed the silage, cautions Virginia Ishler, Penn State Extension dairy nutritionist. She offers these tips to minimize the risks.

Wait 3 to 5 days after an appreciable rain or long cloudy spell before cutting the corn for silage. Then, harvest crops in the afternoon on a warm sunny day.

Since nitrates accumulate in the stalks, cut somewhat higher above the ground than usual. The typical recommendation is to leave 10 to 12 inches in the field. But since a lot of corn is very short this year, so an adjustment to this recommendation may be needed. If in doubt, consult with Cooperative Extension, your crop advisor or nutritionist. Consider testing forage samples before chopping gets underway.

If high nitrate levels are suspected, use forage as silage rather than green-chop. Ensiling reduces nitrates by 50 to 60%. Ideally, allow the forage to ferment for 3 to 4 weeks before feeding to allow the fermentation process to complete.

Any suspect feed should be tested for nitrate levels. The most critical factor influencing possible toxicity is rate of nitrogen intake, which is affected by forage dry matter intake over a given time period.

Feeding practices that regulate dry matter intake can be used to manage high nitrate forages. When stored forages contain more than 1,000 parts per million of NO3-N, intakes generally must be managed to avoid elevated methemoglobin levels in the blood and other toxic effects.

Extreme variations in silage quality will present nutritionists with many challenges. This year's drought conditions will result in reduced yields and the nutritive content won't be consistent or typical. Protein levels in drought corn silage can sometimes be elevated with energy values 80% to 100% of normal depending on the fiber level. It isn't uncommon to see both high and low fiber levels during drought years.

Corn with no ears or poor ear-fill contains most of it's energy as sugar. That can dilute neutral detergent fiber content, but not yield the expected net energy. Carefully scrutinize your silage analysis and how energy values are being calculated before using them in a ration formulation program.
Now's the time to plan out inventory and consult with your nutritionists on alternative forage and feed sources, and their impact on income over feed costs. A good nutritionist can help monitor forage inventory, forage quality changes, and keep your cows milking.