Dealing with Frosted, Immature Corn

Consider the following points when dealing with an immature silage corn crop hit by an early frost.

1. Moisture

The main problem associated with frosted, immature corn silage is the high moisture content. The ideal moisture content for ensiling corn silage in a bunk silo is 65-70%. Frosted, immature corn will have a moisture content much higher than this and must be dried down prior to ensiling. High moisture contents will change the fermentation patterns, increase seepage and potentially have a negative effect on feed intake. Visual determination of moisture “readiness” can be misleading. Although a frosted plant may appear dry due to the appearance of the dead and/or frosted leaves, most of the moisture is actually in the stalk. Frosted corn does not dry down any faster than normal corn and may require many days of dry-down to reach the ideal moisture content.
Plant moisture must be determined using a microwave or a Koster tester. Proper sampling is critical but can be a real challenge because plants in different parts of the field may be at different moisture contents. Harvesting a small representative part(s) of the field and subsampling the chopped load is ideal. A more common method is to hand chop 4-5 plants representative of the field and at the height where the forage harvester would chop. The plants should be chopped finely, mixed together well and a sub sample taken. This subsample would then be analyzed for moisture content. The process will need to be repeated as the crop reaches the target moisture level. As a rule of thumb, whole plant moisture normally drops by 0.5% each day.

2. Feed Value 

Yields of DM will be lower with immature silage. If the grain is at the dough stage, it will have 65-85% of normal silage yield. If no grain is present, expect even lower yields.
Although the feed value of frosted, immature corn will be lower than that of “normal” corn silage, it may not be as low as one might expect. Poor grain yield (ie starch fill) can cause energy to remain as sugar in the stover and leaves thus helping to dilute fiber content. Overall, one may expect slightly higher protein levels, higher ADF and NDF levels and a 10-15% decrease in NEL when comparing immature corn silage to normal corn silage.

3. Nitrates

Frozen corn may contain high levels of nitrates. University of Minnesota research shows that the largest concentration of nitrates is found in the bottom 1/3 of the stalk. Increasing cutting height will help lower the amount of nitrates in the harvested feed but at the expense of dry matter yield. Increasing cutting height from 6 to 18 inches will reduce dry matter yield by about 15%. Ensiling the crop will also result in further nitrate loss. Nitrate levels will be about 50% lower after undergoing the 2-3 week fermentation process. Nitrate testing of silage after fermentation is complete is recommended. More information on nitrates is available on the MAFRI website.

4. Silage Management

Follow proper protocol for silage making. As already mentioned, the most important aspect of ensiling immature corn is to reach the recommended moisture level. Immature corn can be chopped more coarsely than mature corn – aim for a TLC of ¾ to 7/8 inch. Research at the U.S. Department of Agriculture’s Dairy Forage Research Center concluded that frozen corn could be ensiled and would later undergo “normal” fermentation when temperatures warmed (>40° F). Once the corn begins to thaw, lactic acid bacteria counts rise and fermentation proceeds normally.

5. Feeding Management

Once fermentation is complete, the corn silage should be tested for NDF digestibility in addition to the routine analyses. A fermentation profile which includes silage pH, ammonia, lactic, acetic, propionic and butyric acids may also be useful. Dairy producers feeding frozen immature corn silage can expect to feed more grain than usual this winter to compensate for the lower starch content and energy levels.