sealPurdue News

August 21, 2002

It looks dry, but some corn's too wet for silage, specialist says

WEST LAFAYETTE, Ind. – Farmers ready to give up on their arid corn crops and cut them for animal feed might want the inside scoop on the stalks first. The plants could be too wet internally to make good silage.

"Most of us are fooled by the condition of this crop," said Kern Hendrix, a Purdue University Cooperative Extension Service beef specialist. "It looks far drier than it actually is. I was recently speaking with a producer in southern Indiana, and he said he had chopped some corn for green chop to feed cattle and the moisture content was still 80 percent."

When making corn silage, a moisture content between 60 percent and 70 percent is ideal, Hendrix said. That percentage can be in the upper range if silage is being stored in bunker silos or on the ground, but needs to be in the lower range if kept in an upright silo.

"A field test that I use is, if I can squeeze moisture out of the chopped material, then it's too wet," he said.

The dry summer has taken its toll on corn, with many farmers likely to harvest fair to poor crops this fall. Those who also raise cattle and are considering turning their drought-stressed crop into animal feed might find the decision makes sense, Hendrix said.

"The feed value is surprisingly high compared to what most of us would think," he said. "Our data indicate that the feed value of this crop, energy-wise, will be somewhere between 80 percent and 100 percent of typical silage. Usually, the protein level of drought-stressed corn will be higher than typical corn silage – roughly 8 percent. It would not be uncommon to see protein levels of 9, 10 or even 11 percent.

"Producers can take advantage of those protein levels, and reduce the levels of supplemental protein they would normally feed their livestock."

Hendrix recommends producers harvest their poorest fields first.

"They're going to gain a significant amount – if not 100 percent – of the feed value of that crop, although the yield will be low," he said. "That way, they can save their better fields for grain crop."

Stressed corn can have elevated levels of nitrate, a nitrogen-containing compound that converts into plant protein. Excess nitrate is toxic and can cause livestock to become ill or die. Although much is made of the risk to animals, only 18 percent of 70 corn samples tested during the 1988 drought were found to contain hazardous levels of nitrate.

Nitrate toxicity is more common in "green chop" corn, where the corn plant is harvested and fed to livestock while it is still fresh. Producers can have samples analyzed at the Purdue Animal Disease Diagnostic Laboratory or other labs that test plant tissues. Hendrix said producers also can minimize nitrate risks by:

• Raising the cutter bar a foot or more the first few days of chopping, to harvest the less nitric upper stalk.

• Never leaving forage in a wagon overnight.

• Taking additional precautions when harvesting following rain. Nitrate levels often increase following precipitation. "Also, any rainfall that occurs will slow the rate of plant drying," Hendrix said.

• Including low-nitrate feeds as part of an animal's daily ration.

• Gradually introducing livestock to green chop, and feeding the silage in small amounts throughout the day.

"The nice thing about ensiling is that 40 percent to 60 percent of the nitrate is converted to other compounds, or lost," Hendrix said. "So ensiled materials should be safe for feeding in most cases."

Producers who purchase or sell silage should make sure the material is within the recommended moisture content range. A moisture analysis by a reputable laboratory can help, Hendrix said. A few moisture percentage points one way or the other can have a big impact on silage value.

"A rule of thumb is that silage is worth nine to 10 times the price of a bushel of corn," Hendrix said. "Let's say corn is $2.50 a bushel. That would make the silage worth around $22 to $25 a ton, for silage around 65 percent moisture. However, if that silage is 70 percent moisture, then the value will be reduced."

Other issues producers should keep in mind when harvesting drought-stressed corn for silage include:

• Crop insurance – Contact your insurer so that the crop can be appraised ahead of time.

• Loan Deficiency Payments – If participating in this government program, contact a Farm Service Agency office so that yield estimates can be determined on silage acres.

• Pesticides and herbicides – Check labels on products for harvest restrictions prior to cutting. This is vitally important in an early silage harvest.

• Storing – Pack silage in storage facilities in as airtight a manner as possible, and then cover the material in plastic.

Additional silage harvesting and feeding tips are available in Purdue Extension publications "Drought-damaged Corn as Livestock Feed" and "Beef Cattle Management Alternatives for Coping with Short Pasture" by Hendrix and Keith Johnson, Purdue Extension forage specialist. Both are available on the Beef@Purdue Web site.

Producers interested in learning more about nitrate levels should refer to Purdue Extension publication "Forage Nitrate Testing and Making Feeding Recommendations Based on the Results" by Hendrix. The publication, which also appears on the Beef@Purdue site, contains a nitrate percentage chart and contact information for the Purdue Animal Disease Diagnostic Laboratory and other forage crop analysis facilities.

Writer: Steve Leer, (765) 494-8415,

Source: Kern Hendrix, (765) 494-4832,

Ag Communications: (765) 494-2722; Beth Forbes,;

Related Web site:
Purdue University Department of Animal Sciences:

Purdue News Service: (765) 494-2096;

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