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Harvested corn silage: Processing and starch content

Leo Brown Published on 15 September 2011
Hay field

Value of processing and starch content
In the current economy, it’s even more essential to get all of the nutrient value out of harvested corn silage.


Recommendations to harvest at slightly higher dry matter content to maximize starch concentration put an even greater premium on optimum processing.

Why ‘nicking the kernel’ isn’t enough
Given the higher intakes of today’s cows (resulting in feed spending less time in the rumen for digestion), just “nicking” or cracking the kernel is generally not enough.

By increasing the surface area of exposed starch from the kernel, its availability for digestion is increased.

There are laboratory tests available to evaluate kernel processing and determine the state of processing in stored corn silage.

However, monitoring during harvest is needed to ensure adequate processing is being achieved in this year’s crop.

Quick method to check processing during harvest
The specific field conditions, hybrid, whole-plant dry matter and equipment wear all affect kernel damage and can change the processing score across the harvest window.

When results need to be immediate, such as during harvest, here’s a quick “on-farm field test” to assess kernel processing while chopping:
1. Collect a 32-oz. cup of corn silage or take a two-handed scoop (do not grab or you will drop kernels).

2. Sort out and count all half or whole kernels.

3. If you find more than two, it indicates that some starch will not be utilized to its potential at feedout.

Discuss with the chopper operator how to improve kernel damage (e.g., roller mill gap or differential, harvest speed, etc.).

4. Continually monitor kernel damage, evaluating it every few loads.

What if you need more kernel damage?
An easy option to improve kernel damage is to slightly shorten the theoretical length of cut from the standard of 19 mm down to 17 mm.

This small change can make a significant improvement in roller mill effectiveness. However, discuss this with your nutritionist to be sure your corn silage inclusion rate combined with other ration ingredients allow for adequate effective fiber in the entire TMR.

Roller speed differential and teeth per inch
Past focus has been solely on the gap between the rollers. This doesn’t always do the job, to the frustration of both the producer and the custom harvester.

Field experience has shown that chopper manufacturers set roller mill differentials at the factory at anywhere from 10 to 30 percent.

If the roller mill gap is very close (e.g., 1 mm) and kernel damage is less than desired, roller mill “shear effect” may be improved by increasing the differential of the rollers.

Increasing the speed differentials also may allow the roller gap to be increased, thus reducing power requirements and potentially increasing speed of harvest.

The aggressiveness of the roller mill, in terms of teeth per inch, also varies with equipment manufacturers. This should be reviewed, especially if replacing worn rollers or if the chopper will be used to harvest snaplage.

Before making any equipment changes, first check to ensure this conforms with the manufacturer’s recommended operating instructions. And always keep your nutritionist proactively informed of any harvest procedural changes.

More tips to optimize silage value
Intensive management of kernel processing is essential. Delaying feeding of corn silage until it has been in storage a minimum of 60 to 90 days also enhances starch availability.

Caution also should be taken at higher corn silage dry matter (DM) levels in regard to silage preservation.

As whole-corn-plant DM approaches 40 percent DM, moisture may become limiting for adequate compaction and bacterial activity to support a desirable fermentation. Avoid permitting corn silage to exceed 37 percent DM.

More intensive management of moisture can increase energy value and enhance profitability
Pioneer Hi-Bred researcher Dr. Fred Owens has analyzed thousands of silage samples. Dr. Owens quantified changes in quality as corn matures from 30 percent to 40 percent DM.

The data reveals that, on average, a hybrid adds about 0.6 percentage points of starch per each additional point of DM. Simultaneously, for each additional point of DM, corn loses less than 0.3 points of NDFD, on average. Although NDFD is important, the detrimental loss in digestibility is quite small relative to the beneficial gain in starch.

High-starch hybrids’ value for corn silage
Even a 1 percent increase in starch content can have a significant impact on improving your bottom line.

Example: It would take 151 pounds per acre of corn grain to make up the difference between two hybrids (say 30 versus 31 percent).

Assuming 25 tons per acre and $4 per bushel corn grain, that equals $10.75 per acre – or enough energy to support $31 worth of milk at $10 per hundredweight (cwt) milk prices.

Factors affecting quality changes
The exact quality changes that may occur vary depending upon the specific hybrid and overall plant health.

Yet the general trend is clear, and it can be concluded that when plants are healthy, there is economic advantage to permitting corn silage percent DM to reach higher levels within the 30 to 40 percent DM range.

For example, harvesting a typical corn crop at 35 percent DM instead of 30 percent DM could result in a nutritional analysis of 36.0 percent starch instead of 33.5 percent.

In this same example, NDFD may have only decreased from 59.0 to 57.5 percent. Since starch is also a major contributor to yield, harvestable tons would also be expected to increase with this modest delay in harvest.

Growing environment effects
Harvest moisture within normal harvest range may not have a great influence on NDFD, but the growing environment does.

In fact, the growing season has a greater influence on fiber digestibility than any other variable, including hybrid genetics.

Dry weather stress, especially during vegetative growth prior to tassel/silk, significantly increases NDFD. Cool, sunny conditions prior to tassel/ silk also positively impact NDFD.

However, abundant moisture prior to tassel/silk typically decreases NDFD. Alternatively, beginning at the time of tassel/silk, dry weather stress decreases nutritional quality by negatively impacting starch content.

Knowing the effect of the growing season on quality allows one to estimate corn silage quality relative to the previous year’s crop and plan accordingly.  FG

References omitted due to space but are available upon request.
—Excerpts from Pioneer Focus on Forage newsletter